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Perceived relative LED brightness at same current: Blue is brightest?

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741:
The following is pretty subjective...

I put a blue led in series with (in turn) yellow#1, yellow#2, green and red. The setup was simply a variable voltage source (0..5V) plus resistor (220R), and the leds obviously have the same current. The blue always looked brightest, regardles of drive voltage. The brighness of both seems to track quite well, the blue always looks brighter by the same sort of proportion. With the LED Vf drops, this means, I am running it at a low max current (1.3 mA measured maximum).

At the brightness I want (just 0.4mA or so), placing a 10k shunt across the blue evens out the brightness.
Blue Vf changes from 2.63 (no shunt) to 2.59V (with shunt).
Voltage across 220R series resistor moves from 0.1V (no shunt) to 0.121V (with 10 shunt across blue LED), corresponding to a current change in the whole series circuit of 0.021/220 = 0.1mA.
V(blue) = 2.6V, V (yellow) = 1.8V.

See also this link
https://electronics.stackexchange.com/questions/208523/human-perceived-relative-brightness-of-indicator-leds

--- Quote ---"adjusted them to equal perceived brightness...The blue diode was the lowest intensity (mCd) which I could find, and you can see I had to scale its current way back."
--- End quote ---

mikeselectricstuff:
Did you try (cold) white ?

741:
Thanks for your suggestion - just tried it. I'd say the series combination W/B is better balanced brightness-wise than Y/B.

mzzj:
Reds and blues are typically lot higher efficiency than green-yellow, sometimes by factor of ten.

Kleinstein:
Blue LEDs are pretty efficient, but the eye is not that sensitive to blue light. So some GaN based green ones (not the yellow green ones based on GaP or similar)  can be higher brightness to the eye, even though there energy efficiency is often lower.
Another big factor is the opening angle of the LEDs.

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