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Red filter for flashlight

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Old Thursday 6th August 2020, 13:36   #1
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Red filter for flashlight

So I need some creative ideas. I have a flashlight that I use for owls and other nocturnal wildlife (not interested in debating using flashlights with owls), and I'm thinking a red filter will be better for my eyes and that of my subjects. I don't want to get a separate flashlight, I like the one I have.

Any ideas one some sort of material I could use, maybe a rubber gel type material, perhaps with a rubberband? Or something more sophisticated? My flashlight is about 4.5 cm in diameter.

I suppose a hard plastic that I could cut in a perfect circle and adhere to the front of the flashlight lens may also work, but I would like it to somehow be removable.
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Old Thursday 6th August 2020, 14:09   #2
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You can also get a flashlight that emits red light by itself. They are more efficient because red light generating LEDs are more efficient than filtering white light and it doesn't scatter a beam like a filter that you put in front does.

However, I have done an experiment to use red light for looking at nightjars instead of using a (very weak) white flashlight and concluded that red light doesn't work that well (for me at least). First of all, human eyes are not very sensitive to red light, so it needs to be pretty bright to see anything, which defeats the purpose. Second, it is much more difficult to see plumage if you have only one colour. So I will use a very weak normal torch once again.

If you want to experiment with your original idea (using a filter) anyway, I have in the past used (for other purpose, in the 1980's) gelatine filters from Kodak (Kodak Wratten Filters) that were intended for photography and could be bought with the spectral characteristics that you want and can be cut to size. I'm not sure if they still exist, but this is the first thing that comes to mind.
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Old Friday 7th August 2020, 08:59   #3
Mike C
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Without getting into the "why on Earth would you be thinking about doing this" debate.....

Just get some toffee wrapped in red transparent wrappers.
Enjoy the toffee and attach the cleanEd transparent red wrapper over your torch.
Cheap, quick and easy.

Amongst the current box of goodies in my kitchen there are flavoured toffees in yellow, red, green and purple wrappers.
Plenty of choice
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Old Friday 7th August 2020, 16:58   #4
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I think the easiest would be to check online for diameter of your flashlight, and for filters with this diameter for sale (no matter which brand). They cost just few dollars normally. I currently have a filter from another flashlight.
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Old Friday 7th August 2020, 19:43   #5
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Red cellophane thin enough to project light is available from art shops and sometimes as gift packaging. Some plastic filters attentuate the light massively, so shop around and look for reviews.

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Old Saturday 8th August 2020, 07:56   #6
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All experiments that I have done with a red filter on a flashlight have always turned it into a floodlight (it scatters the beam). But what you want is a proper beam with a good throw.

Therefore, you are much better off using a flashlight with red LEDs. Don't waste your time and money fiddling with filters. Three years ago I bought a red flashlight for just 11.42, including a rechargeable li ion battery and charger, and it has an adjustable beam with a zoomlens, so it can make a nice narrow beam with massive throw. You'll never achieve that with a filter placed in front.

However, as I wrote before, I reverted back to a (much weaker) white light because I find it difficult to distinguish features in red light.

Nowadays I just use a (weak, white) headlight (the ones you use for hiking) and because it is handsfree I can observe the birds through my binoculars. This way I don't need much light and still see nocturnal birds reasonably well. I can use a low light level that doesn't seem to disturb the birds much. I have observed nightjars and potoo this way and they just went on with their business, catching moths and kept returning to the same perch. I kept the light level so low that I lost most colour vision, but I still preferred it over red light. Also, with white light you still have the option to switch to a higher level for a few seconds to see the bird's colours, which might disturb the birds, but at least you have this option and you can decide whether this is appropriate or not.

But anyway, red light may work for you, so just get a cheap red LED flashlight online and see if you like it. Even a cheap one will outperform anything that you can achieve with a white flashlight + home-made filter.
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