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

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DrG:
Although it may not be terribly relevant or useful, this thread reminded me of playing around with an RGB color mixer some five years ago. I started thinking about how I could get a handle on the equal brightness for the R-G-B elements.

The psychophysics of “brightness” is not simple. One way that I thought about was to attach a pot to each element and then adjust them until they appeared to be equally bright. Of course, the elements in an RGB do not make that easy. You could use three of the same kind of RGB LED and hope that the specs were close enough between them. Otherwise, I would need to alternately turn each on and off while trying to "remember" the brightness.

While the adjustment to achieve the perception of equal brightness is essentially sound, it was a PITA – more accurately a pain in the eye. I just did not feel comfortable staring into LEDS.

FWIW, I ended up using a BH1750 https://www.mouser.com/datasheet/2/348/bh1750fvi-e-186247.pdf  light sensor with different resistors that I had on hand. From the resulting lux values, I generated the graph below. The horizontal dotted line represented “equal brightness”.  The resistor values falling on that line were what I chose for the R-G-B segments, respectively.

Not saying it is the best way, but It worked pretty well for me.



xavier60:
I use cheap bead type LEDs to repair light fittings. I like to replace the old LEDs with new one of the same color temperature.
To me the LEDs classed as neutral white look brighter than the warm white ones.
BTW, I have used over a thousand of the 3W types without a single failure so far. http://i1195.photobucket.com/albums/aa385/brlux/LED/Bead%20LED.jpg

rdl:
Older yellow-green LED on left at 15 mA next to a modern InGaN 525nm green LED at 300 uA (yes, micro amps).



Original post:

https://www.eevblog.com/forum/beginners/how-can-i-determine-the-resistor-value-for-an-unknown-type-of-led/msg2893554/#msg2893554

I wanted a rude username:
Also depends on ambient brightness, because while the photopic (light-adapted) eye is most sensitive to 555 nm light (slightly yellowish green), the scotopic (dark-adapted) eye is most sensitive to 507 nm light (cyan-green).

This works in favour of the (still relatively inefficient) InGaN green LEDs compared to expensive but highly efficient phosphor-based true greens, if you're using them at night.

Also both the true and perceived colour of InGaN LEDs will change slightly depending on their brightness. When running one extremely dim (uA range) at night, it'll appear thoroughly cyan!

tooki:

--- Quote from: 741 on May 01, 2020, 04:15:26 pm ---Absolutely; it is well known the eye has best response to green. I naturally expected green would be brightest (which it was not) - but my own tests are very subjective, I realise that. I agree with the observation that blue LEDs are more recent - up to a point - but blue has existed for many years now.


--- Quote ---But you can get a green LED which is as efficient as the most efficient blue LED (or at least close), in which case it looks brighter at the same power input
--- End quote ---

Um... I am running the same current in my tests, and that was my 'constant' for brightness comparison no attempt to equalise power was made... But still - is this something you can say you have tried for real - or that someone else has tried for real?

--- End quote ---
You’re still not getting it. You’re working from the assumption that current is directly related to light output when comparing LEDs. It’s not. As others have already explained, there are gargantuan differences in LED efficiency (that is, the amount of output per input).

Modern-type LEDs are insanely efficient. At the 20mA that used to be “normal” for an indicator LED, they’re downright unpleasantly bright.

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