jtr1962 said:Reds are certainly more efficient than whites with a red filter, probably by a factor a three or four. However, in terms of overall efficiency emitting visible light whites are actually better, although not by much. I recently measured some 9000 mcd reds at roughly 40 lm/W. The same company now has 11,000 mcd with a similar beam angle which should manage in the high 40s. The better 5mm whites are in the 60 to 75 lm/W range according to my tests. However, that doesn't tell the whole story. In terms of converting energy to light the best whites are about 20% efficient while the best reds are probably around 35% or so. The lumens per watt are less simply because our eyes are less sensitive to narrowband red light than to white.
Yes, at 20 mA drive current reds use less because their Vf is in the 1.9 to 2.1 volt area instead of the 3.2 to 3.6V typical of whites.