HLMP-D150 5 mm / T1-3/4 and HLMP-K150 3 mm / T1, with 60-65 degree rated viewing angle and millicandela at 1 mA of 3 and 2 mcd respectively. ADDED 2/20/2023: HLMP-D101, differing from HLMP-D150 mainly by having performance specified at 20 mA instead of 1 mA, and specified to produce 70 mcd at 20 mA. These are offered by Broadcomm and Everlight. Broadcomm took over production of these HLMP LEDs by Avago, which took over production of them by Agilent, which took over production of them by Hewlett Packard.

All of these pure red LEDs are available from Digi-Key.

UPDATE 6/20/2020: Green LEDs of the CP41B series by Cree, one of which was previously mentioned here, are discontinued. Other through hole green and blue LEDs by Cree have extremely high efficiency at low currents and are bright enough to use as indicator lamps at .5 milliamp or less, .3 mA or less for green ones.

Cree LEDs with part numbers starting with C5SMF-GJ have a wide and oblong beam, with a nominal viewing angle of 100 by 50 degrees. There has been some notation of their viewing angle as 100 by 40 degrees. They are oval, nominally 5 mm wide in the wider dimension. Their viewing angle is wider in the wide dimension. They are good in applications where they are aimed horizontally or nearly horizontally. Update 8/12/2020 C5SMF-GJE-CX14Q7T2 is consistently bright at low currents and expected to be consistently bright enough for usage as indicator lamps at .2 mA, very likely consistently bright enough to use as indicator lamps at .15 mA. I got over 10 mcd at .07 mA.

Nichia NSPG320C / NSPG320CS (clear, 3 mm / "T1")

This LED has a nominally 45 degree viewing angle, but in my experience (one lot) it is almost as "wide angle" as most 60 degree ones.

My measurement of a few units of one lot is 25-40 millicandela at .21-.22 milliamp. I found brightness to be typical of LED indicator lamps at .1 mA with this lot. Expect other lots to have brightness "at least sufficient for use as indicator lamps" at .25 mA.

Nichia NSPG520AS (clear, 5 mm / "T1-3/4")

This LED has a nominally 45 degree viewing angle, but in my experience (only one lot) it is almost as "wide angle" as many 60 degree ones. It is slightly less "wide angle" than the 3 mm one above.

My actual measurement of a small number of units of only one lot is 25-40 millicandela at .15-.16 milliamp. I found brightness to be typical of LED indicator lamps at .07 mA with this lot. I expect other lots to have brightness "at least sufficient for use as indicator lamps" at .22 mA.

UPDATE 7/28-29/2009 on Nichia NSPG520AS - I tested one at 1.69 mA and achieved .58 lumen and about 800-900 millicandela. (NOTE 8/6/2020: Testing of more units of this LED on 7/28/2009 indicated average of .597 lumen at 1.69 mA.) I found this generally visible in direct sunlight and usually uncomfortably bright to look at in normal room lighting, to extent of mildly putting spots in my eyes, at 1.69 mA.

Nichia LEDs are best available in USA from their own USA sales office. Some above Nichia models may be discontinued, or may still be available maybe with a later revision version letter in their part numbers, while maybe not being in their current catalog.

TT Electronics / Opto Technology OVLLG8C7 is a lower cost 5 mm LED available from Digi-Key. It generally achieves at least 3 mcd at .35 mA according to my testing of units probably from only one lot. However, I expect that part number to reliably produce at least 2 mcd at .44 mA unless static electricity damage has been incurred. These have a wide nominally 85 degree viewing angle.

Kingbright WP9294ZGC/G - 5 mm, rated 60 degree viewing angle, available from Digi-Key. Expect better performance than that of the above TT/Optek LED, but it costs more. Expect reliable usefulness as an indicator lamp at .4 mA, probably even at .3 mA. Update 9/7/2022: This is a 4.8 mm / "straw hat" LED.