I am relatively new to smartphones but I have already found 2 good astronomy apps that I like to use while observing: SkySafari (sky charts) and Astro Panel (weather). While SkySafari has a night (red) mode, the display seems a bit bright. Astro Panel doesn't offer a night mode. Further, if you need to use the phone for calls, email or such, the screen is really bright.
Enter the Staunton River Star Party and vendor AstroGizmos. I spoke with Jeff of AstroGizmos about my problem and he quickly produced a red acrylic film large enough for my Android phone at the price of $10. While the price seemed high, the phone was a night vision destroyer, so the deal was made.
I carefully trimmed the film to fit my phone with an Exacto knife. The film came in a plastic sleeve but there was some dust on it anyway. Following instructions that came with the film, I washed and dried it to remove dust and oils. This worked well and I applied my new screen protector over the clear one already on my phone. It adhered nicely with no bubbles.
Next came the closet test - off to a pitch black closet with phone and the new red screen protector applied. I found that SkySafari + red film was good, but SkySafari in night mode + red film was best. Astro Panel + red film was a bit bright but ok for a quick weather check. Other phone functions were legible and much more night vision friendly.
Care and feeding...
Removing the film is not difficult at all since it lies on top of a clear screen protector. If the fit is difficult, you can use a toothpick to lift a corner of the film. Washing with soap and water seems to work well for removing gunk. I store mine with a clear film I got with my clear screen protector because the fit and material are made exactly for that purpose.
The acrylic is thicker than the clear screen protector that I use on the phone. I expect that the red acrylic will be durable enough to last quite a while.
The executive summary...
This purchase was a no-brainer. The phone is useable in the field for all its functions without destroying your dark adaptation. It is easy to maintain and install. AstroGizmos sells several sizes - my phone required the $10 size; you may need the $5 size. You can check out these red screen protectors at: http://www.astrogizmos.com/TransVinyl1.htm