Why is the light in a darkroom always red?

Answer 1

It isn't always. There are also gold-colored darkroom lights.

The silver chloride compound used in black and white photography only responds to certain wavelengths (roughly, colors) of light. It does not respond well to those particular red and gold colors, and so it is safe to use them in a darkroom.

For color photography, however, the film will respond to any wavelength of visible light, and so no lights at all can be used.

Answer 2

Because the energy of red photons is lower than the energy of other colors (due to reds longer wavelength) As a result, any 'stray' light won't do as much damage to undeveloped film as another wavelength might.

Doug

Answer 3

What the others said is true, but also, our eyes are more sensitive to red than other colours as low level, they are least sensitive to blue, so a blue light with as much energy as a red one cannot be seen by us so well.