LED Brightness Chart

[Orthus]

Okay, I feel the need to explain this stuff since I'm an overblown, egotistical academic that works in computer vision and cognitive science...

Light has to penetrate a bunch of nerve related wet-ware to get to the photoreceptors (see first image). The center of your retina (the macula) has a higher concentration of red and green receptors than else where. The peripheral part of your retina has a higher concentration of blue receptors (see grossly simplified second image). That's why police cars have both red and blue...attention in front, attention from the side. Green would be a poor choice since it means "Go!" in many cultures. It's also why blue neon signs are hard to focus on at night. That said, our photoreceptors respond better to green. That is, hit a red cone with pure red and the signal produced is less than a green cone hit with pure green. That's why a green 5mW laser looks MUCH brighter than a 5mW red laser. Green is perceived to be brighter at the same energy level.

Finally, the LED's themselves are more or less efficient depending upon the color and the quirks of the particular die when it was made. I'm not an EE, so optoelectronics is outside my comfort zone. I don't know if the green LED's are more efficient than red, which would further explain the difference in brightness.