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Red Vision Flashlight |
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Star gazers learn very quickly the need for a flashlight that only emits red light. This is not only so that you can see without ruining your eye's dark adaptation, but so that you don't bother those around you. This shows you how to make one for yourself very inexpensively, or even free if you made the Laptop Cover.
Fig. 1
Here in the US, an import company called Harbor Freight Tools has advertised coupons for a couple of years now to get a free LED flashlight for just visiting the store - I managed to collect several of these freebies. One of those is shown on the right in the photo above. Above left is a piece of the rubylith sheet that I got to make my laptop cover. After tracing the diameter of the flashlight opening with a sharp pencil on a corner of the rubylith, I simply cut out the corner and then cut inside the line, trying to be somewhat careful. The rubylith circle was then a tad large, so I continued to make very small cuts until it fit on the lens of the flashlight. I then placed the rubylith on the lens with a drop of clear glue. The picture above shows the flashlight on with the rubylith in place, but the camera overexposed the light making it seem much brighter than it is.
Fig. 2
Cutting a perfectly round film is difficult, but it doesn't have to be perfect. I just took some black acrylic paint and painted around the perimeter (and not all that neatly, either, since it doesn't need to be) which not only blocked any stray white light, but acted a glue as well. Should the 9 LEDs prove to be too much light, I can always go back and paint a black dot over one or more of the LEDs to dim it. They are not high intensity LEDs though, so I think it will be okay. I "tested" the flashlight at an observing site one night with one of the commercially available red flashlights (it used a red emitting LED instead of a red filter) sold for astronomical use, and the light emitted appeared to be about the same. Although this idea has been around since just a few milleseconds after the big bang, what is new for me is getting a useful astronomical device for free! If you don't already have some rubylith, you might ask at your astronomy club for some spare pieces, or better yet, get a sheet to divide up at a meeting where everybody can bring in a free flashlight!
The Bino Chair
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