The Most Efficient LEDs!

(And some really bright ones also)

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News and links! UPDATE 10/2/2019
General Notes and Disclaimers
Pure Red / Deep Red LEDs - 14 to 39-42 lumens/watt, 51 - 73.5% efficient
Orangish Red LEDs - 46-96-100-105 lumens/watt
Red-Orange LEDs - 66-123-148 lumens/watt
Truly Orange LEDs - 54-102 lumens/watt
Yellow and amber LEDs - 34-161 lumens/watt, with a way for 50-110-plus for less-amberish yellow.
Non-Phosphor Yellow-Green LEDs - 14 lumens/watt.
Non-Phosphored Green LEDs - 70-143-152 lumens/watt.
Better InGaN green LEDs achieve 120-160-165-235 lumens/watt at reduced currents
Phosphored Green, Light Green and Yellow-Green LEDs - 191-215-219-237 lumens/watt.
Blue-Green LEDs - 57-93 lumens/watt
Blue LEDs - 25-45 lumens/watt (and up to 59 lm/w at decreased current)
Royal Blue LEDs - 50-plus - 56 - 74 maybe 76 % efficient, 22-27 maybe 30 lumens/watt
Broadband / Multiband Blue LEDs - 50-51 lumens/watt
White LEDs - 100-192-222 lumens/watt
Warm White LEDs - up to 211 lumens/watt
Increased Efficiency of InGaN LEDs at lower currents
Important Notes on Gallium Nitride and InGaN LEDs!
LEDs with high candela "beam candlepower" figures
Notes on Where To Get Efficient LEDs
Converting / comparing lumens, candelas, millicandelas

News and links!

UPDATE 2/27/2016 this 3/26/2014 Cree press release:

Cree announced 303 lumens/watt at 350 mA. I did not see mention of die size in this press release, as in whether it was a roughly 1 mm square or larger. Correlated color temperature was mentioned - 5150 K.

UPDATE 3/18/2013 this 2/27/2013 Cree press release:

Cree announced 276 lumens/watt at 350 mA. I did not see mention in this press release of die size, as in whether it was a roughly 1 mm square or larger. Correlated color temperature was mentioned - 4401 K.

UPDATE 9/15/2010 - Nichia is mentioned by this LEDs Magazine 9/6/2010 news item to have achieved:

* 135 lumens/watt at 1 amp through an LED lamp having four 1x1 mm dice in series, 1,913 lumens from approx. 14.2 watts. The color temp. was mentioned as 4700 K.

* 183 lumens/watt at 350 mA in a lamp with a 1 x 1 mm chip. (added 8/11/2011)

* A 4600 K LED lamp with a .45 x .45 mm die (larger than the usual generally roughly .3 x .3 mm die in most low power LED lamps) achieving 250 lumens/watt at 20 mA.

The above article mentions that manufacturing techniques necessary to achieve such efficiency are costly, and that Nichia is not prioritizing getting such efficient LEDs onto the market if they are dispropotionately expensive for their light output.

UPDATE 11/2/2004 - WITH THANKS TO FANS OF THIS WEBSITE:

In August 2004, Osram announced a prototype of an orange-red LED that achieved 108 lumens/watt, producing over 2 lumens at 10 mA with a voltage drop presumably of about 2 volts.

IMPORTANT NOTE: Some laboratory prototypes mentioned above are not yet in production even if years old! Barriers apparently include but may not be limited to patents held by competitors, also cost of production with materials and processes used to achieve higher efficiency. Also, gallium nitride based LED chips just may not be cheap (substrate material is generally about 9 on the Moh's hardness scale where diamond is 10). Production of chips of size favoring a more optimum lower current density may price such things out of the market or increase the size of optics needed to control where the light goes.

General Notes and Disclaimers:

Luminous efficacies were largely determined by one or more of several methods, mostly almost laughably crude. I give NO warranty as to accuracy. I have at times slightly changed my estimates for some models. Your mileage may vary.
Unless otherwise noted, luminous efficacy is stated for a 25 degree Celsius (77 degree F.) ambient with a current of 20 milliamps (350 mA for heatsinkable models) in an environment that does not build up heat around the LED, unless otherwise is stated. Heatsinkable models are generally stated to achieve their claimed performance when cooling is sufficient to cool either the heatsinkable surface or the junction temperature to 25 degrees C.

Red, orange, yellow, and yellow-green models (other than high power / heatsinkable ones) mentioned here generally have maximum efficiency at currents around 15-25 milliamps. Efficiency of these is typically less at low currents of a few milliamps or less. The decrease is not as bad with GaAlAsP and "T.S." AlGaAs and the most efficient InGaAsP red ones as it is with most other InGaAsP (orangish red through yellow-green).
Most ultrabright blue, blue-green, non-yellowish green, and white LEDs have luminous efficiency that increases with decreasing current, although the increase will reverse as current decreases below the current at which efficiency is maximized. This current is usually 1-3.5 mA for most blue and green low power LEDs and 2.5-7 mA for most white low power LEDs. For high power LEDs with 1 mm square dice, the current that results in maximum efficiency is typically 25-80 mA for white, and 15-45 mA for blue and green ones with dominant wavelength of 465 to 535 nm.
Please beware that performance of many LED models at currents below a few tenths of a milliamp or a percent or so of maximum rated current may be unreliable.
There may be significant tolerance in light output. Your mileage may vary.

Some of these LEDs radiate light of slightly different colors in different directions. This is most apparent with some white models and some non-phosphor yellow and yellow-green models.

PLEASE NOTE that the lumen per watt figures in this document are lumens of light produced per watt of electricity delivered to the LED. Some LED manufacturers state much higher figures, of lumens per watt of radiated light. This "high figure" is typically around 60-100 for red, 130-180 for orange-red, 220-265 for red-orange, 440-500 for yellow, 400-660 for green (656 for HLMP-C615 by Broadcom, formerly by Avago, Agilent and HP, 650-656 for Broadcom LEDs with peak and dominant wavelengths 555-560 nm), and around 50-90 for blue. The purpose of this "high" figure is for conversion between radiometric and photometric units for the emitted light. If the conversion efficiency and the "high" lumen/watt figures are both known, multiply them to get the lumens out per watt in.

Beam brightness and width figures below are mostly ones claimed by manufacturers or sellers.

Most Efficient Deep Red / Pure Red LEDs - 14-39-42 lumens/watt, 51 - 73.5 % efficient

UPDATE 8/1/2017 The LEDEngin LZ1-00R202 at 1000 mA and 25 C is claimed to have typical "wall plug efficiency" of 51%, with a typical peak wavelength of 663 nm, which indicates typically 26 lumens/watt.

Spectral analysis of a discontinued older LedEngin model indicates dominant wavelength of 643-644 nm and luminous efficacy of the emitted light to be about 60 lumens per emitted watt.

Update 8/1/2017 Osram GH CSHPM1.24-4T2U-1 and GH CSSPM1.24-4T2U-1 appear to me to be good for typically 42 lumens/watt at 350 mA at 25 degrees C, 39 lumens/watt at 80 degrees C. Their radiometric efficiency is typically 70% at 25 C. The GH CS8PM1.24-4T2U-1 has these same ratings, but a narrower beam angle where internal reflection losses are typically slightly greater.

UPDATE 7/30/2018 Cree XPEEPR-L1-0000-00C01 produces 425 mW minimum, 437 mW typically at 350 mA with a typical voltage drop of 2.1 volts at 25 degrees C. This is typically 59% conversion efficiency and means typically 35 lumens/watt assuming a typical spectrum with peak wavelength of 660 nm.

UPDATE 10/12/2020 Cree XPGDPR-L1-0000-00F01 produces 500 mW minimum, 512 mW typically at 350 mA with a typical voltage of 1.99 volts at 25 degrees C. This is typically 73.5% conversion efficiency and means typically 25-30 lumens/watt assuming an extrapolated typical spectrum with peak wavelength of 670 nm. I plan to do spectral analysis of this LED in late October 2020 to refine my estimate of lumens/watt.

Update 7/23/2011 Philips-Lumileds LXM3-PD01 is now available. My guess is that it's LXML-PD03-0260, rated to produce typically 290 mW at 350 mA with a typical voltage drop of 2.2 volts, for typical radiometric efficiency of 37%, at a junction temperature of 25 C. This indicates overall luminous efficacy around 20-22 lumens/watt. The DS68 datasheet indicates achieving around or a little over 92% of this when the heatsinkable surface is at 50 degrees C. Peak wavelength is typically 660 nm, dominant wavelength is not specified. The active material is said to be AlInGaP.

Low power red LEDs with GaAlAsP and Avago's similar AlGaAs in my experience, when doing well, tend to achieve 7-8 lumens per watt. But unlike the more efficient orangish red ones below, they are truly fairly pure red in color, with dominant wavelength (color specification roughly meaning hue) of 637-645 nm, and peak wavelength of 654-665, usually 660 nm.

Some favorites of mine as of 10/21/2020 are Lumex SSL-LX5093SRC/E, Lumex SSL-LX5093XRC/4, and Broadcom (previously Avago) HLMP-D150. A favorite of mine with especially deep red color and good usefulness as an indicator lamp at low current is Kingbright WP7113LSRD (temporarily having a significant lead time at Digi-Key as of 10/21/2020). All of these bright truly red LEDs are available at Digi-Key.

Most Efficient Orangish Red LEDs - 46-96-100-109 lumens/watt

UPDATE 7/24/2017: Cree's XPEBRD-L1-0000-00901 and XPEBRD-L1-0000-00902 at 350 mA are rated to produce a minimum of 80.6 lumens and typically 84 lumens, with a typical voltage drop of 2.2 volts. This works out to 104-109 lumens/watt when the voltage drop is typical. This is with junction temperature of 25 C. With junction temperature of 50 C, expect 89-94 lm/W.

UPDATE 3/22/2011: Lumileds LXM2-PD01-0050, according to its DS-68 datasheet, achieves minimum 50, typically 53 lumens at 350 mA when junction temperature is 25 degrees C, with typical voltage drop of 2.1 volts. This amounts to 68-73 lumens/watt.

UPDATE 12/25/2018: Lumileds LXM5-PD01, according to its DS-68 datasheet, achieves minimum 50, typically 64 lumens at 350 mA when junction temperature is 25 degrees C, with typical voltage drop of 2.1 volts. This works out to 68-87 lumens/watt. This LED was not yet in stock but had an 8-week lead time at Digi-Key as of 12/25/2018.

UPDATE 12/25/2018: Lumileds LXM2-PD01-0060, according to its DS-68 datasheet, achieves minimum 60, typically 62 lumens at 350 mA when junction temperature is 25 degrees C, with typical voltage drop of 2.1 volts. This works out to 81-84 lumens/watt. Although the datasheet gives specifications for this LED, Digi-Key is not yet mentioning it as available as of 12/25/2018.

Expect these LEDs to produce 10-11% less light than mentioned here with more realistic thermal conditions, namely heatsinking that cools their thermal pads to 35 degrees C.

UPDATE 10/16/2020 (date previously typo-ed): The most efficient low power red LEDs I tested so far are 7 samples of Cree C503B-RCN-CXAYCAA2-030 ones. This batch achieved conservatively an average of 68 lumens/watt at 20 mA according to my tests. Forward voltage drop averages 1.955 volts and light output averages 2.66 lumens according to my testing. This is at calculated junction temperature of 25-26 degrees C, expect this 68 lumens/watt figure to decrease to 62-63 lumens/watt at a more realistic junction temperature of 40 degrees C. Dominant wavelength of these 7 samples averaged about 620.5 nm, if this was the 624 nm stated as typical by this LED's datasheet then lumens and lumens/watt would be about 9% less or about 2.2-2.23 lumens (added 3/25/2021) and 57 lumens/watt at a junction temperature of 40 degrees C.

UPDATE 8/3 and 10/13 2020: Some efficient low power red LEDs currently available at Digi-Key that I planned to test in autumn 2020 (and have not yet tested as of 3/25/2021):

Cree CLM1B-RKW-CUbVbAA3: Square root of product of upper and lower limits of its millicandela at 20 mA is 792, which works out to 2.49 lumens if the radiation pattern graph in its datasheet is correct in indicating a lambertian radiation pattern. With typical voltage drop of 2.1 volts at 20 mA, this means typically 59 lumens er watt.

Cree CLM3C-RKW-CUBVAAA3: Square root of product of upper and lower limits of its millicandela at 20 mA is 710, which works out to 2.23 lumens if the radiation pattern graph in its datasheet is correct in indicating a lambertian radiation pattern. With typical voltage drop of 2.1 volts at 20 mA, this means typically 53 lumens er watt.

These Cree red LEDs have their performance specified for junction temperature of 25 degrees C. Light output and efficiency will be a few percent less in a 25 degree C ambient according to thermal resistance and performance of similar LEDs at elevated temperatures.

Most Efficient Red-Orange LEDs - 66-123-148 lumens/watt

UPDATE 4/14/2012: Philips-Lumileds LXM2-PH01-0070 produces minimum of 70 lumens, typically 72 lumens at 350 mA with voltage drop of typically 2.1 volts, maximum of 2.8 volts. This works out to typically 97.9 lumens/watt, minimum of 71.4 lumens/watt. This is with junction temperature of 25 C. Expect about 13% less typically when the thermal pad temperature is at 35 degrees C in continuous operation, which means about 62 lumens/watt minimum, 85 lumens/watt typical.

UPDATE 12/25/2018: Lumileds LXM5-PD01, according to its DS-68 datasheet, achieves minimum 50, typically 90 lumens at 350 mA when junction temperature is 25 degrees C, with typical voltage drop of 2.1 volts. This works out to 68-122 lumens/watt. This LED was not yet in stock but had an 8-week lead time at Digi-Key as of 12/25/2018.

UPDATE 8/2/2017: Osram GA CSHPM1.23-KTLP-W3 and GA CSSPM1.23-KTLP-W3, in stock at Digi-Key, typically achieves 148 lumens/watt at 25 degrees C and 133 lumens/watt at 50 degrees C according to its datasheet. Osram refers to their reddish orange LEDs as amber, while other LED manufacturers refer to their orangish yellow and occaisionally yellowish orange LEDs as amber.

As for low power ones:

UPDATE 10/31/2009: Nichia NSPRR70AS, version with nominally 615 nm dominant wavelength (NSPRR70AS is nominally red): Dominant wavelength of 615 nm has a color that sometimes appears orangish red and usually appears reddish orange. At 50 mA, typical voltage drop is supposed to be 2.4 volts and typical light output is supposed to be 9 lumens. This works out to 75 lumens/watt.

UPDATE 10/12/2009: Osram LA E65F-CBEA-24-1-Z, in stock at Digi-Key, typically achieves 66.7 lumens/watt according to its datasheet. The datasheet states that typical performance at 50 mA is 7.17 lumens and a typical forward voltage drop of 2.15 volts.

Most Efficient Truly Orange LEDs - 54-102 lumens/watt.

UPDATE 8/14/2017: Osram LO E67F-BADA-24-1-Z is rated to typically produce typically 11 lumens at 50 mA with a typical voltage drop of 2.15 volts, which works out to typically 102 lumens/watt.

UPDATE 8/14/2017: SunLED XSM2MOK983W is a 4-lead "piranha" LED that is rated to produce typically 9 lumens at 70 mA with a typical voltage drop of 2.4 volts. This works out to 54 lumens/watt.

Most Efficient Yellow / Amber LEDs - 34-161 lumens/watt

UPDATE 9/23/2019: Nichia NFSY757G typically produces 30.2 lumens at 65 mA with a typical voltage drop of 2.88 volts. This works out to 161 lumens/watt. This LED has a typical dominant wavelength of about 578-579 nm, which is a non-orangish yellow as opposed to the usual orangish yellow with dominant wavelength around 590 nm.

Nichia NVSA119B-V1 and NVSA219B-V1 typically produce 240 lumens at 700 mA with a typical voltage drop of 2.98 volts. This works out to 115 lumens/watt. These LEDs are phosphored ones with the usual amber-yellow color with a dominant wavelength of about 590 nm.

UPDATE 6/20/2020: Osram LCY CLBP-KZLY-5F5G-8E8G-350-S is stated to typically produce 124 lumens at 350 mA with a typical voltage drop of 2.95 volts when the junction temperature is 25 degrees C, which works out to 120 lumens/watt. The square root of the product of its lower and upper limits of light output is 120.6 lumemns, which indicates 117 lumens/watt. This LED uses a phosphor.

UPDATE 6/20/2020: Osram GY CSHPM1.23-KQKS-36-0-350-R18 is stated as producing 76.3-97 lumens, square root of product of these is 86 lumens, at 350 mA with a typical voltage drop of 2.2 volts when the junction temperature is 25 degrees C. This works out to typically 111.7 lumens/watt. Please note that light output and efficiency of non-phosphored yellow LEDs including this one is significantly less with real-world junction temperatures.

UPDATE 10/7/2015: Cree XPEAMB-L1-0000-00901 typically produces 81 lumens minimum, 84 lumens typical with a typical voltage drop of 2.1 volts at 350 mA and junction temperature of 25 C, which works out to 110 low-side, 114 typical lumens/watt. Expect significantly less, often at least 25% less with even generous-side real-world heatsinking due to high temperature sensitivity shown for this amber LED (like non-phosphor amber LEDs in general) in this datasheet.

UPDATE 8/14/2018: Cree XPEBPA-L1-0000-00D01 is a phosphor amber LED that produces 107 lumens minimum, 114 lumens maximum, I figure 110.4 lumens typical, at 350 mA with a typical voltage drop of 3.05 volts at 25 degrees C. This works out to typically 103 lumens/watt.

UPDATE 3/12/2016: Lumileds L1C1-PCA1000000000, a phosphor "amber" LED, typically produces 94 lumens at 350 mA with a voltage drop of 2.75 volts, which works out to 98 lumens/watt, at a junction temperature of 85 degrees C. At 25 C, the DS144 datasheet indicates light output is 1.15 times higher or typically 108 lumens, and the typical voltage drop is 2.85 volts, which works out to typically 108 lumens/watt. At 100 mA and 25 C, the datasheet indicates light output about 31% of that at 350 mA or 33.5 lumens and typical voltage drop of 2.78 volts, which works out to typically 120 lumens/watt.

UPDATE 12/25/2018: Lumileds LXM2-PL01-0000 produces minimum of 80 lumens, typically 110 lumens at 350 mA with a typical voltage drop of 3.05, maximum 3.51 volts. This works out to minimum of 65, typically 103 lumens per watt. This is with junction temperature of 25 C. Expect about 2% less with thermal pad temperature of 35 C.

UPDATE 12/25/2018: Lumileds LXM5-PL01 produces minimum of 50 typically 74 lumens at 350 mA with a voltage drop of 2.1 volts typical, 2.6 volts maximum. This works out to lumens/watt being 55 minimum, 68 low side, 100 typical when the junction temperature is 25 degrees C. Expect about 18% less when the thermal pad temperature is 35 C.

UPDATE 10/7/2015: White LEDs can be filtered to yellow with yellow filters or "lenses". Typically 60-75% of the luminous/photometric output of a white LED gets through as reasonably yellow light. 60-165 lumens/watt (from 100-220 lumens/watt as of mid 2018) is possible by filtering the most efficient white LEDs. The downside is that white LEDs often have worse aging characteristics than yellow LEDs unless they are underpowered.

The loss is greater if filtering to an orangish or "amber" shade of yellow suitable for traffic signals. Phosphor yellow/amber LEDs may be better here.

As for low power yellow LEDs:

UPDATE 10/12/2009: Osram LY E65F-CADA-46-1-Z, in stock at Digi-Key, typically achieves 44.6 lumens/watt according to its datasheet. Typical performance at 50 mA is output of 4.8 lumens and forward voltage drop of 2.15 volts.

As for low power yellow LEDs in my testing:

UPDATE 10/16/2020 Cree C503B-ACN-CY0Z0341-030, 7 samples tested, produces 2.19 lumens at 20 mA with a voltage drop of 1.99 volts, meaning 55 lumens/watt. This is with calculated juncion temperature of approx. 28 degrees C. At a more realistic junction temperature of 40 degrees C, expect 47 lumens/watt.

I expect that others have fair chance of achieving similar luminous efficacy with low power non-phosphor yellow / amber LEDs.

Most Efficient Non-Phosphor Yellow-Green LEDs - 14 lumens/watt

Most Efficient Non-Phosphor Green LEDs - 70-143-152 lumens/watt

UPDATE 9/23/2019: Nichia's NCSG119B-V1 and NCSG219B-V1 typically produce 139 lumens at 350 mA with a typical voltage drop of 3.38 volts. This works out to 105 lumens/watt.

UPDATE 9/25/2019: The above Nichia NCSG119B-V1 and NCSG219B-V1, at a decreased current of 75 mA as extrapolated using graphs in their datasheets, typically produce 37 lumens with a typical voltage drop of 3.04 volts, which works out to 162 lumens/watt.

UPDATE 3/12/2016: Cree XPEBGR-L1-R250-00F02, XPEBGR-L1-0000-00F02, and XPEBGR-L1-0000-00F01 typically produce 126 lumens at 350 mA with a typical voltage drop of 3.2 volts. This works out to typically 113 lumens/watt.

At 150 mA, the datasheet for these LEDs indicates light output being 51% of that at 350 mA with typical voltage drop of 2.9 volts, which indicates 147 lm/W. I expect even greater efficiency at 50-100 mA, typically about or over 160 lumens/watt at 50-65 mA as of 9/25/2019.

UPDATE 12/25/2018: Lumileds L1C1-GRN1000000000 produces minimum of 90 lumens, typically 115 lumens at 350 mA with a typical voltage drop of 3.05, maximum 3.5 volts. This works out to minimum of 73, typically 107 lumens per watt. This is with junction temperature of 85 C. Expect about 1% more with thermal pad temperature of 35 C.

UPDATE 6/22/2020: the above Lumileds L1C1-GRN1000000000, at decreased current of 100 mA, typically produces about 36% as much light as at 350 mA according to the Figure 3e graph in its datasheet (DS144), which means typically 38.5 lumens. Its voltage drop at 100 mA is typically 2.85 volts according to the Figure 4d graph in its datasheet. This means it typically achieves 135 lumens/watt at 100 mA. This is with junction temperature of 85 degrees C.

UPDATE 4/14/2012: Lumileds Luxeon "Rebel" LXML-PM01-0100 is a top brightness rank green one with worst case performance of 100 lumens at 350 mA and worst case forward voltage drop of 3.51 volts. This works out to 81.4 lumens/watt worst case minimum. According to the DS68-1 datasheet, typical overall luminous efficacy at junction temperature of 25 degrees C is 100 lumens/watt at 350 mA (102 lumens, 2.9 volt voltage drop). At 100 mA, the datasheet indicates light output being 38% of that at 350 mA or 38.7 lumens typically and a forward voltage drop of typically 2.65 volts, which works out to typically 146 lumens/watt. I expect even higher overall luminous efficacy around 160 lumens/watt at 50 mA.

Now for low power green LEDs, 70 - 87 - 125 lumens/watt,
even more when underpowered:

UPDATE 8/5/2020: Cree C503B-GCS-CB0C0781, 10 samples received and tested at 20 mA. Average voltage drop was 2.72 volts. Quantum efficiency, conservative measurement: Antilog-mean-log for the lowest 8 of these 10 and 4th-lowest were both 31%. Average photon energy of the spectrum with median dominant wavelength (of 524 nm, noted 8/8/2020) is 2.37 eV based on centroid wavelength of 523 nm. 4th-lowest lumens per emitted watt is 466.3. This works out to conservative-side typical figures of 6.8 lumens and 125 lumens/watt.

UPDATE 8/26/2015: Nichia NSPG510BS (which I have yet to test) has claimed beam candela 45-60% greater than that of the below NSPG510AS as I remember data mentioned in Nichia's website. This means overall luminous efficacy can be anywhere from 87 to 115 lumens/watt at 20 mA.

UPDATE 1/1/2008: I tested several units of Nichia NSPG510AS and NSPG520AS. My tests indicate at 20 mA average forward voltage drop of 3.05 volts and light output ranging from 3.9 to 4.4 lumens. The datasheet says typical forward voltage drop is 3.2 volts. This indicates 61 to 72 lumens per watt overall luminous efficacy.

Better InGaN Green LEDs get 120-160-165-235 lumens/watt at reduced currents

UPDATE 8/6/2020: A lowish median performing sample of one of 10 samples of Cree C503B-GCS-CB0C0781 received 8/5/2020 was tested at 2 mA. Voltage is 2.33 volts. A conservative figure of quantum efficiency is 43%. Dominant wavelength is 531 nm. Centroid wavelength is 529.2 nm, which indicates average energy of emitted photons being 2.34 eV. Lumens per emitted watt is 518. This indicates 1.04 lumen and 223 lumens/watt.

UPDATE 8/9/2020: This same sample of Cree C503B-GCS-CB0C0781 was tested at 1 milliamp. Voltage is 2.27 volts. A conservative measure of quantum efficiency, rounded down, is 44%. Dominant wavelength is 532 nm. Centroid wavelength, longer of determinations from two spectrometer recordings, is 533.4 nm, which indicates rounded-down average photon energy of 2.32 eV. Lumens per radiated watt, lower of determinations from two spectrometer recordings, is 528. This works out to .539 lumen and 237 lumens/watt. A curve fitting method using data I have at other currents indicates 235-236 lumens/watt, so I'm calling this as 235 lumens/watt in order to avoid error in favor of overreporting the overall luminous efficacy of this LED.

UPDATE 8/26/2015: Nichia NSPG510BS is (untested by me) 45%-plus more efficient than the NSPG510AS and 40%-plus more efficient than the NSPG520AS, as I remember and understand data from Nichia's website. This means 165 lumens/watt is somewhat likely and 200 lumens/watt is possible at favorable low currents.

UPDATE 12/25/2007: I just got a batch of NSPG510AS units that average 72 lumens/watt at 20 mA. At 3 mA, they had a forward voltage drop averaging 2.6 volts and produced on average .94 lumen according to my testing, for an overall luminous efficacy of 120 lumens/watt.

UPDATE 2/16/2014: On 7/28/2009, I tested a NSPG520AS at 1.69 mA, and found forward voltage drop of 2.45 volts and quantum efficiency of 29.5%. The color matched that of a Nichia green LED whose spectrum was analyzed with results indicating average photon energy of 2.339 eV and luminous efficacy of the emitted light being 512 lumens/watt. This indicates .597 lumen, conversion efficiency of 28.15% and overall luminous efficacy being 144 lumens/watt.

As for high power LEDs: As mentioned above, the Lumileds LXML-PM01-0100 and some Cree XPEBGR-L1-* LEDs are likely to achieve 160 lumens/watt at 50 mA.
UPDATE 9/25/2019: As mentioned above, I expect Nichia NCSG119B-V1 and NCSG219B-V1 to typically achieve 162 lumens/watt at 75 mA. I expect even greater efficiency of at least typically 165 lumens/watt at 50 mA.

Most Efficient Phosphored Green, Light Green and Yellow-Green LEDs - 191-215-219-237 lumens/watt

UPDATE 9/25/2019: The above Nichia NCSGE17A, at a decreased current of 100 mA, as extrapolated using graphs in its datasheet, typically produces 65 lumens with a voltage drop of 2.81 volts, which works out to 231 lumens/watt.

UPDATE 3/31/2021: Nichia NCSGE17A (G)14) is a version of NCSGE17A with a very yellowish shade of green with dominant wavelength ~ 567-568 nm and about 2% more photometric output than the less yellowish version of NCSGE17A has.

UPDATE 9/28/2019: Osram GT PSLR31.13, more specifically GT PSLR31.13-LUMQ-T1T2-1 typically producves 187 lumens at 150 mA with a typical voltage drop of 6.25 volts. This works out to 199 lumens/watt. This is a phosphored LED with two blue dice/chips. Its color is a slightly whitish, very slightly yellowish shade of green with a typical dominant wavelength of 540 nm.

At 60 mA, this LED typically produces 82 lumens with a typical forward voltage .5 volt less than at 150 mA, or typically 5.75 volts. This works out to 237 lumens per watt. This is extrapolated using graphs in this LED's datasheet.

Now for lime green phosphored yellow-green LEDs:

UPDATED 8/14/2018: Lumileds LXML-PX02, AKA LXML-PX02-0000, is a high power "lime" phosphored LED with dominant wavelength of 566-569 nm and its lowest brightness bin achieves luminous efficacy of 140 lumens/watt minimum at 350 mA when its junction temperature is 85 degrees C. Its datasheet says that it typically produces 184 lumens at 350 mA with typical voltage drop of 2.75 volts, which works out to 191 lumens/watt.

The datasheet indicates that at 25 degrees C, the light output is 1.1 times that at 85 C. The voltage drop is probably the same as with royal blue, or 2.9 volts at 25 C. This indicates typically 202 lumens and 199 lumens/watt at a junction temperature of 25 C.

At 200 mA and a junction temperature of 25 C, the DS68-1 datasheet indicates a typical typical light output at least 58% of that at 350 mA and a typical voltage drop of 2.74 volts, which works out to 117 lumens and 213 lumens/watt. At 100 mA and a junction temperature of 25 C, the datasheet indicates a typical voltage drop of 2.65 volts and a typical light output at least 28% of that at 350 mA, which works out to 56.5 lumens and 213 lumens/watt. I think that the overall luminous efficacy is typically 215 lumens/watt at 120-150 mA.

Update 8/5/2020: Lumileds L128-LME1003500000 is a lime green LED that typically produces 77 lumens according to Future Electronics, 79 lumens according to its DS236 datasheet at 120 mA with a typical voltage drop of 3 volts. This works out to typically 214 or 219 respectively lumens/watt. As of 8/5/2020 this LED was mentioned as orderable by the reel from Future Electronics with none yet in stock, and not yet being mentioned by Digi-Key.

Update 8/5/2020: Lumileds has related "mint" LEDs with a less yellowish or non-yellowish and noticeably whitish shade of green. An example is L128-MNT1003500000, which typically produces 77 lumens with a typical forward voltage of 3 volts at 120mA according to its DS236 datasheet, which works out to 114 lumens/watt.

Update 8/14/2018: Lime LEDs that consist of a royal blue LED chip and yellow-green-emitting phosphor are not on the market with the most efficient royal blue LED chips used in royal blue LEDs that are on the market as of 8/14/2018. If such lime green LEDs were to exist, they would typically achieve about 250-275 lumens/watt at 350 mA.

LEDs of similar color and overall luminous efficacy similar to, maybe slightly higher than that of white ones can be made by suitably adding a suitable fluorescent dye to suitable white or blue ones. That means about 120-220-plus lumens/watt! If you put a white or blue LED into a piece of green-fluorescing yellow acrylic this will probably work! Go Here for LED Hacking for Fun and Danger.

Most Efficient Blue-Green LEDs - 57-93 lumens/watt

UPDATE 3/29/2016: Nichia NCSE119B-V1 and NCSE219B-V1 typically produce 108 lumens at 350 mA with a typical voltage drop of 3.32 volts, which works out to 93 lumens/watt.

UPDATE 6/20/2020: Lumileds L1C1-CYN1000000000 typically produces 100 lumens at 350 mA with a typical voltage drop of 3.05 volts when the junction temperature is 85 degrees C, which works out to 93.7 lumens/watt.

UPDATE 6/22/2020: the above Lumileds L1C1-CYN1000000000, at decreased current of 100 mA, typically produces about 38% as much light as at 350 mA according to the Figure 3e graph in its datasheet (DS144), which means typically 38 lumens. Its voltage drop at 100 mA is typically 2.85 volts according to the Figure 4d graph in its datasheet. This means it typically achieves 133 lumens/watt at 100 mA. This is with junction temperature of 85 degrees C.

UPDATE 5/29/2016: Lumileds Luxeon "Rebel" LXML-PE01-0080 is a top brightness rank "cyan" sometimes-in-stock one with worst case performance of 80 lumens at 350 mA and worst case forward voltage drop of 3.51 volts. This works out to 65 lumens/watt worst case minimum. Typical is 81 lumens/watt. In "real world" heatsinking, these figures can be a couple percent less.

Lumileds LXML-PE01-0070 is more reliably available and has luminous efficiency of 57 lumens/watt worst-case and 74 lumens/watt typical when the junction temperature is 25 C.

Most Efficient Blue LEDs - 25-45 lumens/watt

High power LEDs:

UPDATE 7/30/2018: Lumileds Luxeon "Rebel" LXML-PB01-0040 is a top brightness rank blue one with worst case performance of 40 lumens at 350 mA and worst case forward voltage drop of 3.51 volts. This works out to 32.5 lumens/watt worst case minimum. Typical is 40 lumens/watt according to the "DS68" datasheet. This is at junction temperature of 25 C; expect a percent or two less with good heatsinking.

UPDATE 6/20/2020: Lumileds L1C1-BLU1000000000 produces minimum of 25 lumens, typically 43 lumens at 350 mA with a typical voltage drop of 2.84, maximum 3.5 volts. This works out to minimum of 20, typically 43 lumens per watt. This is with junction temperature of 85 C. Expect strangely about 6% less with thermal pad temperature of 35 C, assuming the unusual blue curve in Figure 2e of the DS144 datasgeet is correct.

UPDATE 6/22/2020: the above Lumileds L1C1-CYN1000000000, at decreased current of 100 mA, typically produces about 36% as much light as at 350 mA according to the Figure 3e graph in its datasheet (DS144), which means typically 15.5 lumens. Its voltage drop at 100 mA is typically 2.63 volts according to the Figure 4d graph in its datasheet. This means it typically achieves 58.8 lumens/watt at 100 mA. This is with junction temperature of 85 degrees C.

UPDATE 7/29/2018: Cree XPEBBL-L1-0000-00301 produces typically 49 lumens at 350 mA with a typical voltage drop of 3.1 volts. This works out to typically 45 lumens per watt at 25 C junction temperature. Worst case minimum at 25 C and 350 mA is 45.7 lumens with a voltage drop of 3.5 volts, which means 37 lumens/watt.

UPDATE 3/31/2021: Nichia NCSBE17A produces typ. 42 lumens at 350 mA with a typical voltage drop of 3.0 volts, which works out to typ. 40 lumens/watt.
As I see data characteristeric curves published by Nichia, NCSBE17A at 100 mA typically produces 15.6 - 15.75 lumens with typical voltage drop of 2.61-2.62 volts. Assuming typicvally 15.6 lumens with typical voltage drop of 2.62 volts at 100 mA, this works out to typically 59.5 lumens/watt at 100 mA.

Now for low power blue LEDs:

UPDATE 8/26/2015: UNTESTED, SIGHT UNSEEN: Nichia has new blue LEDs recently becoming available. One is NSPB510BS, which achieves 25-34 lumens/watt according to my extrapolation from Nichia published data and results of my testing on older models. Expect optical output at 20 mA to be about 22-30 mW, which means conversion efficiency around 34-46 percent.

UPDATE 10/15/2020: Cree C503B-BCN-CX0Y0451, in my testing of 7 samples, had conservative determination of typical overall luminous efficacy/efficiency of 31 lumens/watt at 20 mA. UPDATE 10/16/2020: These 7 samples have dominant wavelength averaging at least 472.5 nm. If their dominant wavelength was 470 nm that their datasheet says is typical, they would achieve 28-29 lumens/watt instead of 31.

I have yet to do testing at lower currents. I suspect my samples of Cree C503B-BCN-CX0Y0451 will achieve about 37 lumens/watt at a current close to 8 mA, and about 40 possibly 41 lumens/watt at 2-3 mA.

Most Efficient Royal Blue LEDs - 50-plus - 74 maybe 76 % efficient, 22-27 maybe 30 lumens/watt

Update 7/30 - 8/1 2018: Cree XQEROY-00-0000-000000Q01 and XQEROY-00-0000-000000Q02 produce 600 mW minimum, 612 mW typical at 350 mA with a tyypical voltage drop of 3.1 volts at 350 mA at 25 degrees C. This means conversion efficiency is typically 56%. Spectrum analysis of a different LED with similar spectrum indicates 48 lumens per emitted watt, so overall luminous efficiency is probably about 27 lumens per watt.

Update 7/30/2018: Cree XPGDRY-L1-0000-00601 produces 730 mW minimum at 350 mA with a voltage drop of 2.82 volts typical 3.1 volts maximum at 25 degrees C. This means conversion efficiency is 67% minimum, 74% low side. If its typical radiant flux at 350 mA is 750 mW, then its typical efficiency is 76%. This is a horticultural royal blue LED with a short peak wavelength of typically 448 nm, and I believe its light has about 40 lumens per emitted watt. This means overall luminous efficiency is typically somewhere around 30 lumens/watt, but it could be less.

This LED is designed for use with much higher current, and its efficiency is less with higher current. Its efficiency at 1500 mA is about .78 times its efficiency at 350 mA, so I think typically about 59% or typically about 23 lumens per watt at 1500 mA. Its lumens/watt at 1500 mA could be less due to its peak wavelength probably being slightly shorter at higher current.

Most Efficient Broadband / Multiband Blue LEDs - 50 - 51 lumens/watt

UPDATE 8/1/2018: Cree XQEAPB-H0-0000-000000401, not cataloged at Digi-Key as of this date, is a "PC blue" LED with luminous flux of 51.7 lumens minimum, 56.8 lumens maximum, at 350 mA with a typical voltage drop of 3.1 volts. This indicates a luminous efficiency of typically 50 lumens/watt.

UPDATE 8/1/2018: Osram LB CL7P-HZJZ-3B6B-Z, listed as obsolete by Digi-Key, produces typically 55 lumens (with a wide range of 39-71 lumens) at 350 mA with a typical voltage drop of 3.1 volts. This means typically 51 lumens/watt.

Most Efficient White LEDs - 100-192-222 lumens/watt

UPDATE 11/18/2019: Seoul Semiconductor S1W0-3030508003-0000003S-00001 is claimed to typically produce 39 lumens at 65 mA with claimed typical voltage of 2.7 volts at 65 mA at 25 C. This works out to typically 222 lumens/watt.

UPDATE 8/2/2018: Everlight 62-227ET/KK7D-3M5050X6Y62629U6/2T/EU of middle brightness bin of T3 produces typically 41 lumens at 65 mA with a voltage drop of 2.84 volts according to the Figure 2 graph of its datasheet. This works out to 222 lumens/watt. Using the 2.75 volt midpoint of its 2.6-2.9 volt range of voltage drop at 65 mA, overall luminous efficiacy works out to 229 lumens/watt.

UPDATE 8/7/2018: The Nichia NF2W757G-V3F1 version with CRI rank of R70 (CRI of 70 min.) and color temperature 5000K typically produces 38.8 lumens at 65 mA with a typical forward voltage drop of 2.73 volts, when its solder pad is at 25 degrees C. This works out to 218 lumens/watt.

UPDATE 5/21/2016: Lumileds L135-4080CA35000P1 typically produces 53 lumens from 100 mA of current with a typical voltage drop of 2.8 volts which works out to luminous efficacy of 189 lumens/watt, although its datasheet says 186 lumens/watt. At 65 mA it typically produces 34 lumens with a voltage drop of 2.72 volts which works out to 192 lumens/watt, although its datasheet says 194 lumens/watt.

UPDATE 8/5/2018: Lumileds L135-4080SA35000P1, L135-5080SA35000P1 and L135-5780SA35000P1, not mentioned at Digi-Key as of this date through 12/6/2020, typically produce (or will produce) 36 lumens at 65 mA with a typical voltage drop of 2.8 volts, which works out to typically 198 lumens/watt, although the DS203 datasheet says 203 lumens/watt.

As of 12/6/2020, the most efficient Lumileds L135 LED being mentioned at Digi-Key is L135-4080CA35000P1, mentioned above.

UPDATE 3/10/2019: Samsung SPMWHD32AMD3XAR0S0 and SPMWHD32AMD3XAT0S0 are rated to typically produce 39 lumens at 65 mA with a typical voltage drop of 2.75 volts. This works out to 218 lumens per watt.

As for high power white LEDs:

UPDATED 1/28/2017: Cree XPLAWT-00-0000-0000V5051 and four other XLPAWT series cool white LEDs produce 513 lumens minimum, (extrapolated) 524 lumens typical, at 1050 mA with junction temoperature of 25 C. With junction of 85 C, minimum luminous flux output is 460 lumens, and typical is 470 lumens. Typical voltage drop at 1050 mA is 2.95 volts at 85 C, most likely 3.07 volts at 25 C. This works out to typically 162 lumens/watt at junction temperature of 25 C, 152 lumens/watt at junction temperature of 85 C.

This is a very high power LED, comfortably producing 776-794 or more lumens at 2 amps when its junction temperature is 85 C, and its absolute maximum current rating is 3 amps.

When significantly underpowered with 350 mA, this LED appears to typically produce (conservatively) 36% of 511 lumens with a forward voltage drop of typically 2.76 volts at 25 C, based on its datasheet. This works out to extrapolated as typically 190 lumens/watt.

Cree claimed in this 5/22/2014 press release that this series of LEDs is to achieve up to 200 lumens/watt at 350 mA.

The datasheet for Cree XP-L LEDs is here.

UPDATE 5/30/2016: Cree XPGDWT-01-0000-00ME3 and XPGDWT-01-0000-00ME2 typically produce 177 lumens at 350 mA with a typical voltage drop of 2.73 volts at 350 mA and junction temperature of 85 C. This works out to 185 lumens/watt. When the junction temperature is 25 C, the voltage drop increases by .1 volt and the light output increases by 11-12% according to the datasheet, so this indicates luminous efficiency of about 190 lumens/watt.

The datasheet indicates that when current is 125 mA, light output is typically about 36% of that at 350 mA, and voltage drop is about .08 volt less than at 350 mA. At junction temperature of 25 C, this appears to be about 70.5-71 lumens with a voltage drop of 2.75 volts when current is 125 mA, which works out to about 205 lumens/watt. According to how I see the graph of relative luminous flux vs. current in the datasheet, I expect about 205 lumens/watt at 25 C to be achieved with current from 125 to 150 maybe 160 mA.

UPDATE 12/22/2018: Lumileds "Luxeon V2" L1V2-5770000000000, L1V2-5070000000000 and L1V2-4070000000000 typically produce 315 lumens at 700 mA with a typical voltage drop of 2.83 volts when the junction temperature is 85 C. This works out to 159 lumens/watt. Worst case extrapolated using datasheets for related parts is 298 lumens with a voltage drop of 3.04 volts, which is 140 lumens/watt. At 350 mA, typical luminous efficiency extrapolated using datasheets for related LEDs is 180 lumens/watt when the junction temperature is 85 C. At junction temperature of 25 C, light output is 6% more and voltage drop is not stated, but other recent datasheets for similar LEDs indicate 4% more, meaning luminous efficiency is 2% more or 183 lumens/watt. Luminous efficiency increases from that as current is decreased to 100 milliamps, maybe even less.

UPDATE 2/27/2016 - As for a Nichia high power LED: The NVSW119B-V1 version with color temp. of 5000 K and the lowest color rendering index rating (none specified) typically achieves 305 lumens at 700 mA with a typical voltage drop of 2.98 volts, which works out to typically 146 lumens/watt. The version with second-lowest CRI (70 minimum) typically produces 302 lumens and achieves 144.5 lumens/watt.

At 350 mA, the typical forward voltage drop is 2.83 volts. Light output is typically 168 and 164 lumens for the lowest and second-lowest CRI versions respectively. This works out to 169 and 165 lumens/watt respectively.

NOTE: All high power white LED data above is from datasheets and datasheet interpretations and not personally experienced actual test results.

UPDATE 5/11/2009 Cecol / Citizen Electronics produces their CL-L233-C13N with nominal light output of 1335 lumens at 720 milliamps with a typical voltage drop of 18.6 volts, which works out to 100 lumens/watt.

Now for low power white LEDs:

UPDATE 6/30/2012: Nichia announced on 5/10/2012 their NSPW510HS-K1, which has a claimed typical luminous efficacy of 170 lumens per watt at 20 mA. Typical light output is 10 lumens and typical voltage drop is 2.8 volts at 20 mA. Nominal beam width is 30 degrees. This LED may have a chip similar to that of NSPWR70CS-K1, which is larger than usual for low power LEDs. The beam may have different characteristics from those of other Nichia NSPW-510 series LEDs.

Update 5/11/2009: Nichia has an extremely efficient 4-lead LED, NSPWR70CS-K1, A.K.A. NSPWR70CSS-K1. At 20 mA, it is said to typically produce 8.7 lumens with a typical voltage drop of 2.9 volts, which works out to 150 lumens per watt. At 50 mA, typical luminous flux is stated as 20 lumens and typical voltage drop is stated as 3.1 volts, which works out to 129 lumens/watt.

I have tested this LED. My testing indicates 140-145 lumens/watt at 20 mA for a few that I have tested.

Update 8/3/2014: This LED may now be discontinued.

UPDATE 10/15/2020: Seven Cree C535A-WJN-CU0W0231 LEDs tested (at 20 mA), results are in, with a conservative typical figure of overall luminous efficacy/efficiency of 100 lumens/watt. Typical voltage drop in my testing of these 7 samples was 3.00 volts, typical light output was determined conservatively as being 6.0 lumens. The dimmest of these 7 samples produced a little over 5.6 lumens and achieved almost 94 lumens out per watt in. (Part number found typo-ed, corrected 11/4/2020.)

UPDATE 10/23/2020: Cree C535A-WJN-CU0W0231 actual conservative test results at various currents less than 20 mA: 115 lumens/watt at 10 mA, 119 lumens/watt at 8 mA, 125 lumens/watt at 5 mA, 127 lumens/watt at 4 mA, 129 lumens/watt at 3 mA, 130 lumens/watt at 2.5 mA (2.5-2.7 milliamps maximizes lumens out per mA), 130-131 lumens/watt at 2 mA with this figure peaking at about 2 - 2.2 mA.

UPDATE 11/2/20202020: Cree C535A-WJN-CV0W0231 is brighter still, typically 10.7 % brighter than C535A-WJN-CU0W0231 according to their datasheet. My test results are only about 3% brighter with about 1% more voltage drop, with conservative average of 102 lumens out per watt in at 20 mA. Note 11/4/2020: I found increased consistency of results with the newer part number.

UPDATE 11/4/2020: Results from testing at currents 2-10 mA are in. Efficiency of C535A-WJN-CV0W0231 improved better than I expected from quick preliminary testing at very low currents as current was decreased from 20 to 2 mA, by a hardly measurably smaller percentage than was the case with C535A-WJN-CU0W0231. My figures for lumens out per watt in, conservatively determined like I did with C535A-WJN-CU0W0231, at all currents from 2 to 20 mA are 2 lumens/watt grerater for C535A-WJN-CV0W0231 than for C535A-WJN-CU0W0231. I figure ratio of light output to current for C535A-WJN-CV0W0231 is maximized at about 2.7 mA, based on my testing of 10 of these. My figures for lumens out per watt in for C535A-WJN-CV0W0231 are 117 lumens/watt at 20 mA, 121 lumens/watt at 8 mA, 127 lumens/watt at 5 mA, 129 lumens/watt at 4 mA, 131 lumens/watt at 3 mA, 132 lumens/watt at 2.5 mA and 132-133 lumens/watt at 2 mA with this figure peaking at about 2-2.3 mA.

Update 11/4/2020: Mouser Electronics had 497 C535A-WJN-CV0W0231 in stock and stated a factory lead time of 3 weeks for units after these 497.
Update 12/20/2020:Digi-Key had none in stock and a minimum order of 500 and a standard lead time of 4 weeks, down from 11 weeks stated on 11/4/2020.

The above white LED lamps have blue chips plus a phosphor to convert some of the blue light to yellowish light of broadband spectral content from mid-green to mid-red. The color is usually a cool white to "daylight" slightly bluish or sometimes violetish-bluish white, usually of about 5000-6500 K. Color rendering index of the most efficient ones as well as most other white LEDs is usually stated as 65 to 70 or 70-plus when stated. There are white LEDs with improved color rendering index, but their overall luminous efficacy is compromised, although not much when the color rendering index is 80 or minimum of 80. Higher color rendering index of 90 or more involves significant reduction of luminous efficiency, although a few white LEDs of such premium color rendering index are now getting slightly more efficient than even T8 and T5 fluorescent lamps.

Most Efficient Warm White LEDs - up to 211 lumens/watt

UPDATE 3/24/2013 This 3/19/2013 LEDs Magazine article mentions a 2700K Samsung LM561B-family LED achieving 130 lumens/watt at 150 mA, and 150 lumens/watt at a lower current, with 65 mA mentioned as a lower current for higher efficiency in another LED in this series.

Increased Efficiency of InGaN LEDs at lower currents

Overall luminous efficacy typically peaks at 1.5 to 3.5 mA and remains above that of 20mA usually at least down to .5-1 mA. Efficiency and light output become less predictable below .4-.5 mA.

White LEDs have most of their photometric output from a phosphor, and so the luminous efficacy of emitted light does not improve with decreasing current as much as with colored InGaN LEDs. In fact, spectral shifting of the LED chip's output away from wavelengths best-utilized by the phosphor can impair overall luminous efficacy at low currents. However, photometric output per milliamp seems to usually improve with decreasing current down to about 6 milliamps, sometimes as low as 2.5-3 milliamps. I have tested three (as of 11/4/2020) low power white LED models by Cree at various currents, and found ratio of photometric output to current to be maximized at 2.5-5 mA, achieving about 1.135-1.175 times that achieved at 20 mA. These LEDs had efficiency maximized at 2-3 mA, with efficiency about 1.26-1.3 times that at 20 mA.

Important Note on Gallium-Nitride LEDs!
Gallium nitride and indium gallium nitride LEDs are fussy, and do not like their ratings to be exceeded. Exceeding 5 volts reverse voltage even with low current is supposedly damaging to them. I suspect that destructive electrolysis is what goes wrong. Peak forward currents in excess of 100 mA may also be bad for low power ones. Many of these LEDs are also supposed to be considered static sensitive.

High candela (beam candlepower) LEDs

Highest millicandela green LEDs that I am aware of as of 6/22/2020: Cree C503B-GAS-CB0F0791, C503B-GAN-CB0F0791, C503B-GAS-CB0F0792, and C503B-GAN-CB0F0792 typically produce 53.65 candela at 20 mA. I expect these to typically produce 6-7 candela at 2 mA. Two of these have been available at least since 5/14/2012. Also Broadcom HLMP-CM1A-560DD, claimed 60.5 candela at 20 mA.

Highest MCD red 5 mm LED lamp at 20 mA that I am aware of as of 6/22/2020: Cree C503B-RAN-CA0C0 and C503B-RAS-CA0C0, claimed 22.45 candela.

Brightest white 5 mm LED lamp at 20 mA that I am aware of as of 5/11/2009 - 3/20/2013: Nichia NSPW500DS (15 degree beamwidth, 27 candela) and Nichia NSPW500GS-K1 (same beam angle, 30-33 candela, but has compromised life expectancy).

Brightest white LED at 20 mA that I am aware of as of 8/2/2020: Cree C503D-WAN-CCBEB151, square root of product of lower and upper limits of intensity is 42.7 candela.

Notes on Where To Get Efficient LEDs

Mouser Electronics is also a good source of good LEDs.

Some good LEDs are available from Newark Electronics. Visit http:/www.newark.com. Duplicate shipping charges may apply if you order more than one type of item not all in stock in the same warehouse.

Future Electronics is the original distributor of Lumileds products and is a distributor of other LEDs.

Nichia LEDs are best obtained from their sales offices. In North America, check out Nichia America. Some Nichia LEDs are available from Future Electronics, sometimes with large minimum orders.

Toyoda Gosei makes bright green and blue LEDs.

Toyoda Gosei LED info is now on the web at http://www.toyoda-gosei.co.jp/led/e-index.html.

Converting / comparing lumens, candelas, millicandelas

A lumen is defined as the "luminous flux" of 1/683 of a watt of monochromatic light that has a frequency of 540 terahertz, or a wavelength of approx. 555.5 nm.
One thing worth noting is that a lumen is defined secondarily, in terms of the candela (which is 1 lumen per steradian), and the candela is defined primarily (it's the "beam candlepower" of 1/683 watt per steradian of 540 THz monochromatic light.)
Light of wavelengths other than 555.5 nm have a different amount of lumens per watt of radiation. The number of lumens in a watt of wavelength other than 555.5 nm is 683 times the photopic function of the wavelength in question, divided by the photopic function of 555.5 nm (which I believe is very close to but maybe not exactly 1).

A recently banned "USA-usual" 100 watt, 120 volt, 750 hour "regular" (A19) lightbulb usually produces 1710 lumens.

Lumens per watt is a measure of efficiency in converting electrical energy to light. Multiply this by the watts dissipated in the LED to get lumens. A typical red, orange, or yellow or yellow-green LED has a voltage drop around 2 volts and is getting around .04 watt at the typical "standard" current of 20 milliamps. A blue, white, or non-yellowish-green one typically has a voltage drop of 3.25 volts at 20 mA and gets .065 watt at 20 mA.

A candela is a lumen per steradian, or "beam candlepower". (Actualy, as mentioned above, the candela is a primarily defined metric unit, while the lumen is defined in terms of the candela.)
So lumens are candelas times the beam coverage in steradians. Candelas are lumens divided by the beam coverage in steradians. Ideally, that is - assuming that all light is within the beam and the "candlepower" is constant within this beam.

So you may now be wondering what a steradian is. It is 1 / (4 * pi) of a whole sphere or 1 / (2 * pi) of a hemisphere or about 3283 "square degrees", to the extent there is such a thing as a "square degree". To get steradians from the beam angle:

Steradians = 2 * pi * (1 - cos (.5 * (beam angle)))

(NOTE: There are a few other expressions equal to this. Proving that is homework for 12th graders taking trig / "elementary functions".)

So if you determine the steradian beam coverage and multiply that by the candela figure (or 1/1000 of the millicandela figure), you get the lumen light output - very roughly! The beam is not uniform and it does not contain all of the light. Obtaining lumens from beam angle and candela can easily be in the +100 / - 50 percent range. Actual lumens are generally higher than predicted by this formula with smaller beam angles of 8 degrees or less since the nominal beam does not include a secondary "ring-shaped" "beam" that usually surrounds the main one. Also note that some beam angle figures are optimistic and could lead one to expect a lot more lumen light output than actually occurs.

Please read my disclaimer.