S/P Ratios of Various Light Sources

New file 2/15/2010, updated slightly 2/27/2016

I have found some published s/p ratios of some light sources to be incorrect. Many incorrect figures appear to me to be incorrectly low ones stated by proponents of one or two particular light source technologies competing against others whose s/p figures were incorrectly stated.

In addition, I have found lack of published s/p ratios of some light sources where this is of interest.

As a result, I have added a chart of what I believe to be correct s/p ratios of many light sources, with sources of data/"data". Much of this data is from questionable to low-traceability measurements, from measurements that I can trace but requiring adjustments whose properness I was unable to "properly" measure, from theoretical calculations of some items that are easy to at least somewhat fairly easy to reconstruct, and from 3 "reconstructions" of high pressure mercury vapor spectral power distribution that I hope I did a good job of pulling out of my hat. Few of these figures are from spectral data that I have both actually seen to extent of knowing whose spectrometer was used and found to not require "adjustments" for clipping, noise, or other factors.

Daylight Light Sources
Incandescent Light Sources
Fluorescent Lamps
HID and Discharge Lamps
LED Light Sources
Monochromatic Visible Lasers
Extremes of s/p ratios


Light Source                  s/p ratio       source / determination
=======================================================================
DAYLIGHT SOURCES
----------------------
Typical "north window light"  2.59          Calculated s/p of 7500K blackbody
Typical overcast sky          2.36          Calculated s/p of 6000K blackbody
Typical sunlight + sky        2.26          Calculated s/p of 5500K blackbody

Typical direct sunlight
plus partial sky              2.1           Calculated s/p of 4800K blackbody

Typical isolated direct
sunlight                      1.99          Calculated s/p of 4400K blackbody

-----------------------------------------------------------------------------
INCANDESCENT SOURCES
------------------------
Carbon arc, plain           1.80-1.83      Calc. s/p of 3800/3900 K blackbody

Short life photo
lamps, 3400K                  1.65          Calculated s/p of 3400K blackbody

Halogen car headlight,
high beam                     1.57          Calculated s/p of 3200K blackbody

Halogen car headlight,
low beam                      1.52          Calculated s/p of 3100K blackbody

50W 12V and 500W 120V
halogens                      1.50          Calculated s/p of 3050K blackbody

Most halogen lamps            1.46          Calculated s/p of 2950K blackbody

100W 120V 750 hour A19        1.42          Calculated s/p of 2875K blackbody
60W 120V 1000 hour A19        1.39          Calculated s/p of 2800K blackbody
60W 130V 5000hr @120V         1.29          Calculated s/p of 2600K blackbody

Incandescent Nightlight       1.12          Calculated s/p of 2300K blackbody

Candle Flame                   .88          Calculated s/p of 1900K blackbody

-----------------------------------------------------------------------------
FLUORESCENT LAMPS
--------------------
"Old Tech" Warm White         1.00          Berman, 1992 (Note 1)

"Old Tech" Cool White         1.48          Rensellaer Lighting Research Ctr (Note 2)
"Old Tech" Cool White         1.47          My calculation from an adjusted
                                            spectrometer-obtained SPD (Note 4)

"Old Tech" Daylight           2.22          Berman, 1992 (Note 1)

2700K CFL                     1.13          My calculation from an adjusted
                                            spectrometer-obtained SPD (Note 4)

T8 triphosphor 730/SP30       1.3           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 830/SPX30      1.3           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 735/SP35       1.4           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 835/SPX35      1.5           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 741/SP41       1.6           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 841/SPX41      1.8           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 750/SP50       1.9           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 850/SPX50      2.0           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 765/SP65       2.1           GE fluorescent lamp catalog (Note 7)
T8 triphosphor 865/SPX65      2.3           GE fluorescent lamp catalog (Note 7)

--------------------------------------------------------------------------
HID and DISCHARGE LAMPS
-----------------------
Low Pressure Sodium            .23          s/p ratio of 589 nm
                                            (Same as Berman, Note 1)

High Pressure Sodium, 35W      .4           Berman, 1992 (Note 1)
High Pressure Sodium, 50W      .62          Berman, 1992 (Note 1) **(Note 8)

High Pressure Sodium, 250W     .63          Rensellaer Lighting Research Ctr (Note 2)
High Pressure Sodium, 400W     .66          Rensellaer Lighting Research Ctr (Note 2)

White HPS, 50W                1.14          Berman, 1992 (Note 1)

Metal Halide, clear, 175W     1.51          Rensellaer Lighting Research Ctr (Note 2)
Metal Halide, clear, 400W     1.57          Rensellaer Lighting Research Ctr (Note 2)
Metal Halide, 400W coated     1.49          Rensellaer Lighting Research Ctr (Note 2)
(All above MH likely Na-Sc)

Xe-M.H. 4200K car HID         1.61          Rensellaer Lighting Research Ctr (Note 2)

H.P. Mercury, 400W clear      1.33          Rensellaer Lighting Research Ctr (Note 2)

H.P. Mercury, 175W clear      1.26          My calculation using a "reconstructed"
                                            SPD (Note 6) (I question the .8 figure
                                            for "clear mercury" from Berman Note 1)

H.P. Mercury, 175W clear                    My calculation using the above
with yellow filter             .89          "reconstructed" SPD with <500 nm
                                            removed (Note 6)

H.P. Mercury, 175W coated DX  1.08          My calculation using a
"Deluxe White", new condition               "reconstructed" SPD (Note 6)

H.P. Mercury, 175W coated     1.08          Rensallaer Lighting Research Ctr (Note 2)

H.P. Mercury, 400W coated     1.09          Rensellaer Lighting Research Ctr (Note 2)

--------------------------------------------------------------------------
LED SOURCES:
-------------

Older white LEDs, ~6000K,                   Calculation from a spectrometer-
blue peak ~465 nm,                          obtained SPD of a Nichia
CRI 75-plus                   2.3           NSPWF50DS (Note 3)

White LEDs, ~6000K,                         Calculation from a spectrometer-
blue peak ~455 nm,                          obtained SPD of a Lumileds
CRI ~70-75                    2.05          Luxeon III (Note 3)

Extreme-effic. white LEDs,                  Calculation from a spectrometer-
~5000K, blue peak ~445 nm,                  obtained SPD of a Nichia
CRI in the 60s                1.7           NSPWR70CSS-K1 (Note 3)

Red LED, InGaAlP                            Calculation from adjusted spectrometer-
(635-637 nm peak wavelength,                obtained SPDs of a red Lumileds
626-627 nm dominant)           .044         Luxeon and Nichia NSPR510CS (Note 5)

Red LED, GaAlAsP typical
(660 nm peak wavelength,
~640 nm dominant)            .02-.022       (Note 9)

Red LED, GaAlAsP                            Calculation from an adjusted spectrometer-
(660 nm peak wavelength,                    obtained SPD of a Panasonic red
low 640s nm dominant)          .019         LED of this type (Notes 5 and 9)

GaAlAsP red LED filtered
by Wratten 92 or Schott
RG-630 deep red filter       .016-.0165     (Note 9)

GaAsAlP red LED filtered                    Calculation from an adjusted spectrometer-
by Wratten 92 or Schott                     obtained SPD of the above red LED with
RG-630 deep red filter         .015         Wratten 92 filter (Notes 5 and 9)

---------------------------------------------------------------------------
MONOCHROMATIC VISIBLE LASERS:
-----------------------------------------------------
405 nm violet diode laser     9.9           s/p of 405 nm using 1988
                                            photopic function

441.6 nm HeCd laser          22.04          s/p of 441.6 nm interpolated
                                            using 1988 photopic function

445 nm deep blue diode laser 23.2           s/p of 445 nm using 1988
                                            photopic function

458 nm deep blue DPSS        24.1           s/p of 458 nm using 1988
                                            photopic function

473 nm turquoise blue DPSS   17.0           s/p of 473 nm

488 nm cyan argon laser
when single-wavelength       11.5           s/p of 488 nm

515 nm green diode laser      3.99          s/p of 515 nm

532 nm common green laser     2.2           s/p of 532 nm

543.5 nm green HeNe laser     1.51          s/p of 543.5 nm (interpolated)

593.5 nm "yellow" DPSS         .181         s/p of 593.5 nm (interpolated)

612 nm red-orange HeNe laser   .071         s/p of 612 nm

632.8 nm red He-Ne laser       .028         s/p of 632.8 nm (interpolated)

635 nm diode laser          .025 - .026     s/p of 635 nm

650 nm common diode laser   .016 - .017     s/p of 650 nm

660 nm high power red laser    .013         s/p of 660 nm

694.3 nm ruby laser            .0107        s/p of 694 nm

==========================================================================
Extremes of s/p ratios
==========================================================================

Extremes for a single wavelength or narrow band of wavelengths:
---------------------------------------------------------------

Extreme deep red
680-686 nm                .010425-.01048    s/p of these wavelengths

Extreme deep red
675-715 nm                .010425-.01101    s/p of these wavelengths

780 nm near/nearly IR          .023         s/p of 780 nm

Match in mid-red to
780 nm for s/p ratio
(which is 638 nm)              .0229        s/p of 638 nm

Extremes for blackbody radiation:
---------------------------------

750K blackbody, minimum
for humans to see at all       .119         calculated s/p of 750K

800K blackbody, minimum
for humans to see w/color      .145         calculated s/p of 800K


Infinite K blackbody                        1-2 million K has calculated
                              3.5           s/p ratio of 3.49-3.493

**
Note 1: S/p ratio figures referring Berman, 1992:
They appear in a 1992 paper of his,
http://gaia.lbl.gov/btech/papers/30844.pdf

Note 2: S/p ratio figures referring to Rensellaer Lighting Research Ctr:
They appear in:
http://www.lrc.rpi.edu/programs/solidstate/pdf/euroLED2008.pdf

Note 3: S/p ratios of these white LEDs was calculated from data from a StellarNet spectrometer, with no adjustments other than the spectrometer software's calibration data for achieving flat spectral response. Calculations used all wavelengths 380 to 780 nm in .5 nm increments, using the 1988 photopic function.

Note 4: S/p ratios of these fluorescent lamps was determined as above in Note 3, except the spectral data files produced by the spectrometer software were adjusted afterwards. The strongest two spectral lines were clipped by the spectrometer or its software. Since the spectrometer is not mine and I was not able to get re-takes, these spectral lines were manually increased in intensity in my files until chromaticity as reported by spectrum analysis software appeared reasonable to me.

Note 5: S/p ratios of these red LEDs was determined as above in Note 3, except the spectral data files produced by the spectrometer software were adjusted afterwards. In wavelength ranges where the data was mainly or effectively exclusively upward spikes of spectrometer noise, the data was manually reduced to zero. After that, the "tails" of the LED's spectrum were manually extrapolated as exponential functions of wavelength, outward in both directions until insignificant, varying exponentially with wavelength at the same rate as within "each of the notable tails", as best as can be estimated, from the portions of these "tails" that outweighed the spectrometer noise. Less care was taken at longer "essentially-infrared" wavelengths for this adjustment.

Note 6: These "reconstructed" spectral power distributions of high pressure mercury vapor lamps are "reconstructed" into a file type that I can analyze from 380 to 760 nm from how I remember high pressure mercury vapor spectra. These are adjusted to make chromaticity and color rendition effects making sense. These are not actual measurements and they are "merely out of my hat".

Note 7: These figures for GE triphosphor T8 fluorescent lamps are from page 4-32 of a GE fluorescent lamp catalog that I found at (now at web.archive.org):

http://www.topbulb.com/find/Catalogs/GE_Fluorescent.pdf

Note 8: This item has s/p ratio that appears to me as somewhat of an outlier to the high side of a trend, although a few lamps of this item type do achieve s/p ratio so high. I expect 50W high pressure sodium lamps to usually have a lower s/p ratio around .5 to .55 (updated 2/7/2016).

Note 9: The deep red LED item actually tested here is a GaAlAsP red LED model that I chose for having a deeper / more-pure color of red than average for these deep red LEDs. I expect s/p ratio of most GaAlAsP and similarly deep red LEDs to be around .020-.022 without filtering, and around .016-.0165 with a Wratten 92 or Schott RG630 filter.


Written by Don Klipstein.

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