Electronic – LED perceptive intensity by Color

I think the problem is a lack of understanding of what one means by "brightness". Brightness is a very ambiguous term. First of all, I'll make the assumption that you are speaking in terms of a human's perception of brightness. This limits our discussion to photometry. You have to now differentiate between two measures of brightness, i.e. Luminous intensity and Luminous flux (or Luminous Power). Luminous flux is the light power emitted in all directions and has SI units of "Lumens". Luminous Intensity is the light power emitted in one solid angle which has SI units of "candela". Think of a solid angle as a cone with it's vertex at the led emitter. You mentioned mcd as units, these are millicandela, so mcd is a measure of Luminous Intensity. You can't directly compare luminous Intensity (candela)) with Luminous Flux (lumens). I did find this tool to convert between the two units, but, it must have to make the assumption that the light is omnidirectional and is only accurate for such lights.

You'll have to get your units straight before you can make sense out of this.

In additon, you have to decide what your objective is. Are you trying to make a light with high luminous Flux or one with high Luminous Intensity? I would imagine that you are going for a light with high luminous Flux or you probably would be speaking of laser diodes instead of LEDs.

So choose whatever package that maximizes your Luminous Flux, i.e. Lumens. You did not provide enough information to give a better recommendation than this. That is, you did not specify any additional design constraints.

It is highly likely that your red LEDs are of lower luminous efficiency than your white LEDs.

Also, driving an LED incorrectly can destroy it or reduce it's output from then on. Such damage can occur almost instantaneously. Red LEDs have lower operating voltages than White LEDs so are more likely to be damaged by the application of a constant voltage that is too high and not current limited.

The efficiency of LEDs varies widely. It can be expressed in lumens/Watt = l/W.

The best white and the best red LEDs have similar enough l/W ratings that both should appear about equally bright when driven with the same power input. White LEDs typically have operating voltages = Vf in the 3.0 - 3.6V range and red LEDs have Vf = 2.0 to 2.5 Volts. So a red LED would need about 50% more current to achieve the same power as a white LED as Power = V x I.

You state the LED output range as 500 - 20,000 mCd. That's a 40:1 brightness range.

Note that candela are a measure both of energy out and area of illumination. Less area = more brightness for the same light energy.