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Flashlight for Astronomy – How To Choose One?

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To be honest, this is one of those cases where I don’t think it’s possible to give a single brand or model the honor of being named “the” best astronomical red flashlight. This is largely going to be a matter of personal preference. But, with that said, we can certainly discuss the features to look for in a red flashlight, as well as some particular models that may or may not meet your needs.

Why Do You Need One?

Without going into the details (because that’s something for a whole different article), red lights are important for astronomy because they are less likely to mess with the dark-adaption of our eyes.

When we are in the dark, the pupils in our eyes dilate and the photosensitive pigments in the cells of our retinas build up more, making our eyes more sensitive and able to see more and more with less and less light. The longer we stay in the dark, the more adapted our eyes get. Unfortunately, even a little stray light can completely wipe out that adaptation, putting us back to the beginning. If you turn on your phone while sky-watching, you’re doing just that. 

But our eyes are less sensitive to red light. And because of this, less damage is done to our adaptation by the red light. So when we use red lights at night, while it will have some effect on our adaptation, it’s minimal. For this reason, people who spend a lot of time in dark environments prefer to use red lighting when they need just a little light.

Astronomers need them to get around observing area, for setting up and taking down equipment in the dark, for reading our maps and charts, and for finding that eyepiece or filter in our kit that we want to use. If we were to turn on a white flashlight, we could watch hours of dark adaptation disappear in a flash.

Several companies that make telescopes and observing equipment, including Orion and Celestron, offer the best red flashlights. Several other companies that have little or nothing to do with astronomy also offer them. And, of course, prices vary from the very cheap to the fairly expensive.

So, which one do you choose? 

Red Only, or Red and White?

One of the first things to consider is whether you want a red-only light or a light that’s capable of both red and white (or even multiple colors). Having the ability to switch between red and white can be handy, and make the flashlight a multi-purpose tool, not just for astronomy.

Orion, for example, offers a few different options. Their Red Beam II light is red-only, while their DualBeam LED Flashlight offers both options.  They also have a RedBeam Mini version that’s small enough to keep in your pocket.

One thing to keep in mind, however, is that if you do have a dual-purpose light, there’s always a chance you could accidentally turn on the white instead of the red. If you frequent star parties or observe with groups, this can be a bit of a problem. It’s one thing to ruin your own dark-adaptation, it’s another thing altogether to do it to a larger group.

I own a dual-purpose light that happens to have separate buttons for red and white. I keep a piece of take over the white, just to be safe. It doesn’t stop me from using it, but it makes it easier to identify when I’m about to hit the wrong button.

Another option is to get a white flashlight that comes with a red (and/or other colors) filter. The upside here is that when the filter is in place, you’re less likely to accidentally turn on white light. If you want/need dual-purpose, this may be a good option. The only real downside is the off-chance of losing the filter.

Required Brightness of Flashlight

The next thing to consider is brightness. Just because the light is red doesn’t mean it won’t degrade your night vision; it just has less impact. A bright red floodlight will still nuke your dark adaptation. At my astronomy club’s dark site, we’ve had to ask a few people in the past to bring a smaller, dimmer red light the next time they come out.

One nice thing about two of the Orion lights I mentioned above is that they do come with brightness controls, allowing you to dim them as needed.

When it comes down to it, you want to use just enough light to meet your needs at the time. If you’re just switching eyepieces and need to read the markings, you don’t need a huge, bright red light. If you’re trying to read a chart, you might need something a little brighter, but still not anything that’s likely to disturb anyone around you.

If your light is too bright, you might need to do something to dim it (such as covering some of the front of the light with tape to block all but a small amount of light). Some lights do have dimming options, and this is definitely a feature to consider.

Form Factor

Next, let’s consider the form factor. Do you want a traditional cylindrical flashlight? Maybe a clip-on or headlamp? How about a little pocket sized light?

Whatever type you get, I recommend one that’s at least small enough that you can hold it in your mouth for a second or two if you need to. Headlamps can be handy, but they have a tendency to be fairly bright, and if you happen to look up at someone, you stand a chance of dazzling their eyes or even messing up their night vision.

On the other hand, a hand-held can be a real pain if you’re trying to set up or take down your equipment in the dark. Of course, there’s nothing saying you can’t have more than one with you to handle different needs.

Personal Experience

I have four that I use fairly regularly. My main one is this Smith and Wesson tactical flashlight.  Intended for law enforcement or emergency workers, it lasts a long time on a set of batteries, is very rugged, and can be pretty bright. The main downsides to this one are that it can be too bright at times, it’s easy to hit the wrong button, and it’s a pain to use (other than holding it in my mouth) if I need two hands.

I also have a smaller light similar to this one that’s red only. This one isn’t as rugged, but has a lanyard to keep it around my neck. It’s fairly bright, but not as bright as the first. It’s a good balance between size, reliability, and brightness.

Next up, I have a headlamp that does both red and white light, like this one. It’s ideal when setting up and taking down equipment. The rest of the time, I keep it in my kit. It can be too bright for reading charts or eyepieces, but it is good if I have to trek across my club’s dark site to get to the bathroom.

Lastly, I have a small single-led keychain light similar to this. It runs off a coin battery (and seems to run forever!) and puts out a surprising amount of light for a single LED. The only real drawback is that it’s small enough that it’s easy to lose. If it’s not turned on and I drop it in tall grass, it’s a goner.

Dealing with Laptops, Phones, and Tablets

While we are on the topic of red lights, let’s also consider what to do with your laptop, phone, or tablet.  If you use any of these devices in the field (such as for telescope control, for controlling astrophotography equipment, or for charting or logging visual observations), just like a flashlight, these kinds of screens can mess with your night vision.

Some people solve this by using a “red theme” on their device. These “red” themes use mostly red and black fonts and graphics to provide a “red” view that has less impact on your night vision.

But whether it looks red to you or not, it’s actually putting out multi-spectral light. It won’t preserve your night vision as well as you think, and it is likely to annoy others around you (if you’re not observing alone). Furthermore, there’s always the chance that another window could pop up or jump to the foreground of the screen that’s not affected enough by the theme.

For this reason, having actual red filtering is always the best option.

Non-Touch Screens

Unless you have a touch-screen laptop, the best option is still clear red acrylic, which is often referred to as Plexiglass. There are several places you can find this online, including Amazon. I purchased the 1/8 inch thick version in an 18 by 36 inch sheet. It was enough for three laptops with some leftover. It was surprisingly inexpensive and easy to cut with a hacksaw or rotary tool.

If you go this route, some people prefer to cut it to fit within the screen bezel of their computer. I recommend against this unless you have tools that allow you to cut very accurately. I cut mine large enough to fit over the front of my laptop screen entirely and used either a couple of pieces of tape or a couple of large rubber bands to hold it in place.

Touch Screens

If you have a touch screen or need something for your phone or tablet, the heavy acrylic is too thick to read the touch on the screen. For this, then, you need something much thinner.

The old standby that most people I know recommend is a product known as Rubylith. While it was originally a brand-name, it has come to be a generic term for a number of similar products from a variety of manufacturers. I can’t vouch for all versions, but the ones I’ve tried allow touch-sensitive devices to function, albeit with somewhat reduced sensitivity.

The best option I have found, however, is the kind of gel filter sheets used for stage lighting. A single sheet is enough to dim and filter a phone, tablet, or laptop and still transmit your touch through to the screen. You can find these on online sites like Amazon or from local theatrical supply stores.  While I found Rubylith difficult to cut precisely to fit inside my phone case, the lighting gel sheets I’ve found were easy to cut to exact sizes.

While I still recommend a physical filter over a theme option, some newer devices do offer a usable option.

OLED Screens

The reason most video screens are a problem is the backlighting, which is usually white. More recent technology, however, such as OLED screens, works a little differently.

Traditional color LCD and LED screens have a pixel matrix that produces the image, but it needs light shining through it from behind to be seen. This is why the black on most such screens isn’t really black, it’s a very dark gray. 

But on OLED screens, the pixels provide their own illumination. As such, if you tell all of the blue and green pixels to stay off, then only the red pixels will light up, providing truly red light.

On newer Apple devices, you may be able to use the tinting controls to set a red theme that’s truly red because it only uses the red elements in the pixels. I know that some Android devices offer the same ability (though, being an iOS user, I can’t tell you how to do it – you’ll have to do a Google search on that).

In the end, there are a wide variety of options available to you. It’s impossible to say which is the “best” flashlight solution for a given user. I hope that I’ve provided you with some insight into your options.

Good luck and clear skies!

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