Red Flashlights for Astronomy: Guide & Reviews

Amateur astronomy is a hobby that offers peace, beauty and knowledge in the great outdoors (even that great outdoors is nothing more than your backyard.) This exciting pastime is freely available to everyone, when all you need is little more than a blanket for settling down, and a clear open view.

That said, astronomy is definitely a hobby that benefits from technology and handy accessories. One of the most overlooked and underrated tools is also one of the most valuable in any stargazer’s kit: a red flashlight for astronomy.  Unless you are simply lying back and pondering the universe with your naked eyes, you are going to have a setup which requires you to see in low light situations. From adjusting the settings on your telescope, to viewing your star charts and making notes, or even for just pouring coffee – fumbling around in the dark is not ideal.

You may think to do this by any light possible, but that is actually the last scenario you could hope for.

Dark Adapted Vision

Why do astronomers specifically use red flashlights? It has do with something commonly called dark adaptation. There are two levels to how dark adaption works.

The first level is simply the size of our irises. Our irises close more and are smaller in bright light conditions. This helps to protect our eyes from becoming overwhelmed, which could be potentially harmful and cause long lasting damage. The opposite happens in low light conditions. The irises open and become bigger to allow more light to pass through. The shift in the size of the irises is relatively quick and is noticeable too. We can see this happening after we sit outside on a bright day and then enter a shaded house: everything appears quite dark and indiscernible for a minute or so, because of the change in our irises.

True dark adaption also occurs on a chemical level. Our retinas are made from cones and rods; both which receive light in unique ways. Cones are less numerous, but they come in three different types. Each type of cone has its own sensitivity to different wavelengths of light. This is how we can detect a rainbow of colours. The retina contains many more rods than cones, but there is only one type of rod. This mean that rods cannot distinguish different wavelengths of light like cones do. However, rods are far more sensitive to light than cones.

Regardless of their differences, both cones and rods become ‘blind’ to light if they are overexposed. We can clearly see the effects of our eyes being overexposed when we stare at a bright source for an extended time, then turn our vision to a white wall or sheet of paper. The afterimage is imprinted on the white surface. The chemical effects of light overexposure to the cones and rods is once again different. For cones, the chemical reset is fairly quick and the afterimage fades relatively quickly. The sensitive rods, on the other hand, need more time to chemically adjust after being overwhelmed, and the recovery can take up to half an hour, if not more.

Our rods are actually overexposed during the day due to all the light they receive in these conditions. They are overwhelmed and their sensitivity is “shut off”, in a sense, to protect them. However, something interesting happens at night in low light conditions: they are no longer overexposed, and the chemical change that happens in low light conditions means that their sensitivity is effective. Our eyes become dark adapted, and that sensitivity takes in all the light available. On a night out stargazing, the sensitivity of the rods once dark adapted brings the night sky to life. You are technically able to see more. Objects will have finer clarity and detail, and you can see increasingly dimmer celestial objects as your eyes adjust.

There is a catch though: rods become overexposed very easily. It does not take a lot of light, nor does it take a lot of time for the chemical change to take place again. If your eyes are dark adapted and then exposed to bright light, the rods will be “blinded”, and they will chemically adjust (and the irises will close as well) in response to this. This is the last thing you want while observing the heavens, as it can take more than 30 minutes for our night vision to return.

The good news is that rods are not very sensitive to red light, or light with a wavelength of 650 nanometres and less. You can readily use a red flashlight for all your astronomy needs without spoiling your night vision and hence preserve your precious time stargazing.

Best Red Flashlights

Here is a look at some of the best red flashlights for all your astronomy needs.

Celestron 93588 Astro Night Vision Flashlight

The Celestron Astro Night Vision uses two red LED lights which fully retain night vision. This flashlight has the convenient feature of adjustable levels of brightness: very dim light for reading star charts while you observe, and a brighter light for seeing as you pack up and go. It runs on a 9 volt battery which is included in your purchase. The design is not the sturdiest, but it definitely delivers what it offers when handled with some care.

Carson RedSight Red LED Flashlight for Astronomy

The Carson range flashlight contains 9 red LED bulbs, designed to do all your astronomy tasks on a night out without risking your night vision. Despite the good intentions of the design, some users do feel that the light is too bright when compared with superior makes. However, it suffices for personal use and is reasonably priced. It also has a strong design with a rubber textured grip for easy use, and includes a clip for attaching to belts and backpacks. The flashlight uses 3 AAA batteries which are not included in the purchase.

Orion 5756 Daulbeam LED Astronomy Flashlight

The Orion Dualbeam offers the best of both worlds in one handy flashlight: a dim red light which preserves night vision while stargazing, and a bright white light for packing up and making your way around in the dark. A wonderful added feature is an intensity wheel, which allows you to set the levels of intensity for both the red and white lights from dim to bright. Included in the purchase is the 9 volt alkaline battery the flashlight runs on. Orion offers a great design which won’t disappoint – the only downfall is the higher price.

Wayllshine High Power One Mode LED Red Flashlight

The single mode flashlight from Wayllshine will be a great investment for any amateur who does not wish to go through different brightness and light settings. It is simply matter of turning the flashlight on and being ready for use. It does have one additional feature: you can slide the head of the flashlight back and forth to be able to zoom in and out. The flashlight has a high beam rage of 150 yards plus. You have a choice of running the device on one 145000 battery or one AA battery – the latter being preferable as the flashlight is actually dimmer operating on the AA battery. Neither battery is included.

HQRP 9 LEDs Red Flashlight for Astronomy

If you want a cost effective, entry level flashlight which is solely for backyard use, then the HQRP does the trick. The flashlight operates at around 650 nanometres – which will certainly protect night vision – but many users feel it is brighter than higher end red flashlights, and do not recommend it for star parties. The flashlight has a convenient UV meter, which measures exposure to ultraviolet light. It runs on 3 AAA batteries which are not included.

Is a Red Flashlight DIY Possible?

It is tempting to think that you can simply wrap some red cellophane around a normal flashlight and voila – the perfect answer to retaining your night vision. It is not actually that simple. Not all red filters are made equally. Many of these DIY filters do not block out higher wavelengths of light sufficiently enough to truly maintain one’s night vision.

They can be helpful in reducing bright light, even though it is not at the level of true red flashlights. These flashlights can be quite reasonably priced for the quality you are getting. Regardless, if you are truly in a pickle and need to go the DIY route, there are three tips below, each with varying levels of effectiveness.                                                                  

Note: never take a DIY red flashlight with you to star parties. Their reliability is questionable, and you do not only risk ruining your night vision, but the night vision of the other partygoers too.

Method 1: You will need an energy efficient flashlight, red tail light repair tape and scissors. Cover the lens of your flashlight with the tail light repair tape, and trim so that the fit is perfect. Repeat this method two or three times so that the filter is darker.

Method 2: In this method, you take red cellophane (like the type you can find with sweet wrappers) and put layer upon layer of the cellophane over your flashlight. You then keep the layers of cellophane in place with a strong rubber band which is big enough to be tied over the flashlight several times.

Method 3: All you need for this DIY project is some dark red nail polish. Paint several coats of the polish directly onto the lens of your flashlight. It requires a little patience as each coat should dry before applying the next.

Conclusion

There is a great variety of red flashlights available for your amateur astronomy needs, and purchasing one which fully preserves your night vision is highly recommended over adapting your own flashlight with the DIY filters.

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