The best nights for sky viewing are dark and clear. But how do you see to set up your telescope or read star maps or instructions? What you need is a red flashlight. This article covers how to improvise if you don’t have one. It also has a couple you might want to look at purchasing for night vision during those dark nights outdoors.
Why use red light for night vision?
Why is red light good for stargazing? Red light does not disrupt the forming of rhodopsin, a chemical released by the body when our eyes detect low light for roughly 20 minutes. This chemical aids our night vision and came about to help us detect threats at night.
So give yourself at least 20 minutes if you want better night vision, but the longer the better. It can take several hours for your eyes to become fully adapted to the dark and reach optimal low light sensitivity, according to physicist, Dr Christopher Baird.
Why use red torch light over a normal one at night? White light disrupts the advance of night vision. It shrinks our pupil and this reduces the amount of light entering our eyes. This suggests we’ll see more clearly once our eyes are adapted (takes about 20 min) with red light at night than with the normal bright flashlights.
Submariners and other professions having to go from well lit premises to the outdoors are familiar with how red light preserves night vision.
red flashlights in astronomy
What use is a red torch in astronomy? Astronomers use red flashlights to set up, read charts, make adjustments, and find their way in the dark. Red light preserves their dark-adapted vision, enabling them to observe faint night-sky objects.
Compare this to bright light, which switches off the rhodopsin for night vision.
Imagine yourself observing the sky at night and wanting to read a sky chart, check your device, or look up instructions — you’ll need light to see these. Especially if you are a beginner learning the ropes of how to use your new telescope for viewing the planets. Or if you have those extra eyepieces you’re wanting to get to know. Red light is what you need for night vision.
As Jim O’Connor of the Tucson Amateur Astronomy Association explains: “It only takes a few seconds of bright light to cause the rhodopsin to decay…” and this is why astronomers use red flashlights when setting up, re-configuring, or refering to planispheres.
Red light torch app
You can use a red flashlight app, if you don’t have a flashlight that’s red. This is one way to improvise. For Apple, check out NightVision Light at the App Store and for Android, Red Telescope Flashlight at Google Play.
DIY red flashlight
How do you make a red light in astronomy? Here’s how to make a red light torch by simply adapting a conventional flashlight:
- Get some red cellophane and cover the front of the torch or flashlight with layers of the cellophane and then secure these layers with a rubber band. Trim the excess red cellophane and there you have it.
It’s as easy as that. You can get red cellophane online at Amazon.
- Or you can fit red gel light filter pieces over the lens. Art supply stores stock these, but they are also available at Amazon (click on image below to see details and price).
Where to buy red light torch
You can buy red light torches or flashlights online at Amazon and at astronomy speciality shops or techno gear shops. Here are a couple to consider…
Rechargable red light torch
A rechargable flashlight is handy. This one has a USB so you can charge it in your vehicle or using a solar charger or battery bank. It’s also waterproof.
Rechargable waterproof red flashlight
available at Amazon
Lightweight small red light torch
For a flashlight you can stick in your pocket or clip on your belt or carry bag, you can’t go past this lightweight LED model…
Single Mode Red LED Torch Zoomable
Available at Amazon
If you want to free your hands, you can use a red headlamp. The problem with these is that they can get annoying when you are trying to look through the eyepiece of the telescope.
Important accessories for astronomers are observers’ flashlights that shine a very pure red light.
Every backyard astronomer should have a red flashlight in their kit. They are essential for navigating in those best dark places, reading a planisphere, and adjusting settings on the telescope. The best ones are astronomy grade red flashlights. But, if you are just starting out, why not use an app on your phone or get by with making your own — For how to make a red flashlight for astronomy – scroll up.