LEDs - Intensity of Different Colors

[Rick Hughes]

As has been mentioned by various folks in various topics, there are significant differences in perceived brightness among LED lights. To me, the blue can be overwhelming, green less so. Red seems about right, and yellow looks anemic.

Which leads me to two questions ...

First, are there different LEDs inside the cap which account for the difference?

Second, are the intensities likely to be 'normalized' as improvements are made, or is it more likely that the mass market accepts this as standard LED design?

My LOR channels are limited to a single LED color which allows me to moderate the intensities ... but it seems like a lot of unnecessary effort. And I haven't converted my yellow incandescents to LEDs in hope of better color performance.

Rick

[Jerry Budelman]

Hello Rick,

Different color LEDs result from a different chemistry within the LED itself. Three things (or more) affect the perceived brightness of the color. One is the human spectrum sensitivity. The eye is more sensitive to some colors than others. So for a given luminance rating, one color will seem brighter than another. Second, the different chemistries (e.g. LED internal construction) provide different luminous efficiencies. The white LEDs are a little different. These typically use an ultraviolet LED which excites a chemical within the LED to produce a white light. This is smewhat similar to how a flourescent light works. Third, the construction of the lens in the LED string greatly affects brightness by directing the emitted light to, or away from the viewer.

Almost all common LEDs are rated for about 20-30 milliamperes of current. The higher efficiency units provide more light for this power level and I suspect that over time the efficiencies of all colors will gradually increase, although I suspect they will not converge to "equality". The more efficient LEDs are more expensive which is also why you see variations among vendors.

I have made a mini-megatree that uses three different LED colors (R,G,. The LEDs are the "polka dot" style wide angle lens units, and each triad in mounted in a homemade reflector (1/2 of a ping pong ball, sprayed with silver paint). These 3 LED triads are extremely bright and I can create a wide range of colors by varying the proportion of each.



Hope this helps.



Jerry Budelman