Electronics > Projects, Designs, and Technical Stuff
Perceived relative LED brightness at same current: Blue is brightest?
Siwastaja:
--- Quote from: 741 on May 01, 2020, 04:15:26 pm ---
--- 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
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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?
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High-intensity green Vf may be actually very close to the Vf of a blue led, so current is almost ~ power. Do note that different blue emitters vary between 3.0 and 3.7V on "typical" Vf. A high-intensity modern green is easily over Vf=3.0V.
And yes, I have actually, for real, used RGB emitters where the green is visually brighter than the blue, for the same current, or for the same power, as well. Human eye is more sensitive to green, so all that is needed to make this happen is to have the green as efficient as the blue.
OldEE:
Granted this is subjective but in our server room, a few years ago now, from 20-30 feet the blued leds appeared to be considerably brighter than other color leds.
bson:
--- Quote from: 741 on May 01, 2020, 04:15:26 pm ---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?
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I've calibrated the brightness of Kingbright APTD1608LZ (grn, 0603) and the red and blue counterparts to use for PCB indicators.
Here are the colors, If, Vf at If, and limiting resistor value for a 3.3V supply for me to empirically match their brightness to a reasonable level. (If you feed them 1mA they're so bright you'll see spots.) Again, this is for PCB indicator use, not a flashlight or other illumination.
GRN, 25µA, 2.75V, 22kΩ
BLU, 280µA, 0.80V, 8.87kΩ
RED, 67µA, 1.80V, 22kΩ
It's perfectly possible that the blue is barely conducting, and may well have a higher maximum brightness - at much higher currents.
This works great for me, because I tend to use mostly green indicators. Red and blue is more unusual.
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