How red light headlamp preserves your night vision
If you own a headlamp, you probably know about how red light mode is better to use in the dark than white light. Red light preserves your night vision, but have you ever wondered exactly how?
It’s relatively simple. Your eyes have photoreceptors (neurons) in the retinas, called rods and cones which convert light into electrical signals. These electrical signals travel to the brain through the optic nerve and your brain converts these inputs through your visual system into what you actually will see. This is your sight.
Cones for day
Cones are active at high light levels and don’t function in low light. They create colour vision, and spatial orientation.
Rods for night
Rods are responsible to convert images in low light, and are more sensitive than cones, but are not sensitive to colour. It’s your rods that produce the images you see at night.
Within the rods is the chemical Rhodopsin is what actually allows night vision to happen. In the dark, it takes about 30 minutes for this chemical to form so you can see. It can easily be destroyed when exposed to light, and it again takes up to 30 minutes to regenerate again. Most of your night vision does return though within 5-10 minutes of exposure to low light despite the Rhodopsin taking so long to re-form.
Many headlamps have a red light setting. Image from Outdoor Gear Lab
The colour red has a longer wavelength than other colours. According to wikipedia, Rhodopsin in the human rods is not sensitive to these longer red wavelengths, so this is why traditionally many people use red light to help preserve night vision. Red light only slowly depletes the rhodopsin stores in the rods, and instead is viewed by the red sensitive, or the light-sensitive, cone cells.
There are about twice as many cone cells as rod cells, rod cells are more sensitive in general, but not to colour.
How to preserve night vision
As mentioned above, some spectrums of light cause complete ‘bleaching’ of Rhodopsin, and the loss of night vision. But they are less sensitive to the colour red within longer wavelengths of light. Exposure to any light, including red, will destroy your night vision eventually, but with red it will take a lot longer than with white LED light.
Try this
A quick field experiment will show you how your eyes adjust to the dark. Move from a light environment into a dark one, and see how hard it is to see at first. Then try this: before you go to into the dark, close your eyes and count to ten. Now open your eyes in the dark, and you’ll note you’ll be able to see better than if you were just to “shock” your eyes with instant darkness.
If you’re looking for a headlamp, you might want to make sure it has a red light mode. Check out our list of how to choose the best headlamp for your needs.
- How to experience the world while isolated at home - April 21, 2020
- How to prevent and treat hypothermia - February 21, 2019
- How to layer with your down jacket - November 28, 2018
We write rarely, but only the best content.
