Popular Mechanics (USA)
Headlamps are often outfitted with multicolor LEDs. Understanding which is best for what purpose requires brushing up on your biology. “Color is not in the retina. It’s not some reflex tied to wavelength,” explains Bevil Conway, who has a Ph.D. in neurobiology and runs a National Institutes of Health–funded research lab that studies color and cognition. “It’s actually this quite elaborate, sophisticated operation of interpretation that the brain is doing.”
That process starts when the millions of rods and cones at the back of the eye absorb light. These photoreceptors are tuned to react to different wavelengths and operate under different lighting conditions. Rods only respond in very dim light, whereas the three types of cones—respectively most sensitive to long, middle, and short wavelengths—do the work under normal circumstances. So choosing between white and colored light lets us see our surroundings in different ways.
To see the most detail and color,
stick with this neutral light. But in total darkness, use the highest settings judiciously. Bright light creates a glare that causes our rods to shut off, thereby hampering our night vision in the process.
This common colored light, processed from long wavelengths, is best for preserving your night vision because it doesn’t oversaturate your rods. That means they will still work (and you can still see) when you turn the light off. Switch to red when you want to chat face-to-face with a buddy without blinding them or when you want to hide from bugs. (Most insects have photoreceptors that can’t register red light.)
Although it’s rare to find in headlamps, green light makes it easy to see at relatively dim settings. Thank your Land M-cones for that; both are most sensitive to yellow and green light.
Rarer still, dim blue light is the hardest to see with and, contrary to popular belief, won’t help you track a trail of blood when you’re hunting. That’s because your relatively few S-cones absorb the long wavelength red and reflect shorter, blue wavelengths that don’t look markedly different under your headlamp. Limit the blue to mood lighting.