A light that is safe to use in a darkroom because it does not affect the light-sensitive materials being used.
Safelights are important for making pictures and are used in special rooms.
Examples:
The photographer used a safelight in the darkroom.
The red safelight helps the photographer see without hurting the pictures.
The safelight is on in the darkroom.
The safelight is like a superhero for pictures.
The safelight is the only light that can save the pictures.
The safelight is a special light for special rooms.