I often read about people not having time to order an official turtle safe flashlight prior to a trip. This prompted me to do a little research, I have found a couple of apps that will do in a pinch.
For Android users :Download “Red Telescope Torch” for the play store. This one lets you adjust the brightness of your screen by sliding a toggle on the bottom of the screen.
https://play.google.com/store/apps/details?id=appinventor.ai_salcangeloso.RedVision
For Apple users : ISO 10 has a setting in which you can change the color of your screen to red. See instructions here >
A Better Red-Light Filter for Your iPhone
An App to try >
https://itunes.apple.com/us/app/astronomy-flashlight/id301350393?mt=8
I am sure there are more but this will get you started. I have not tried any of these yet but will test the android versions in the future and let you know my thoughts.
Happy turtle watching !