How to ‘Safelight’ your iPhone
Light from smart phone displays will harm light-sensitive photographic materials such as film and paper. Do not use electronic displays in film-safe, total blackout areas when film is exposed and being processed. For photographic papers, which are not sensitive to specific parts of the yellow-red spectrum, some smart phones may be modified to emit a ‘safe’ display. The following directions work with iPhones running iOS 10.1 and higher:
Go to Settings > General > Accessibility > Display Accommodations > Color Filters > slide to ‘on’ (right) position
Then, in the drop-down menu that appears, select ‘Color Tint’
and slide INTENSITY and HUE to the extreme right side.
This will shift the display to a photo-safe red, and should be fine for viewing any app in situations requiring red safelight work. That said, I would still recommend reducing the overall screen brightness level to less than 30%. If you slide the upper screen display’s palette viewer from the default pencil array to the middle ROYGBP grid, you will notice that the ‘actinic’ green to purple wavelengths are now displaying as variations of mid red/grey to black.
To switch back to the normal display, go to Settings > General > Accessibility > Display Accommodations > Color Filters > slide to ‘off’ (left) position.
From this point on, every time you want to switch to the red channel display, navigating to Color Filters and sliding to the right will turn the display to red.
Caveat emptor: Photo materials should be exposed to safelight sources for as little time as possible, and no closer than 2 feet.