Do not fog the photo paper

To make a black and white silver print, the negative is projected onto a paper that reacts to light.

One of the main concerns is to avoid fogging the paper by exposing it to undesired light.

Since working in total darkness is impractical, we take advantage of the fact that silver paper is insensitive to certain wavelengths of light, or more simply put, to light of a certain color.

Light of this color is called inactinic, meaning that its radiation has no noticeable chemical effect on photographic paper.

A bulb that emit only light of this color is called a safe-light.

Brown/orange or red light?

Ilford recommends using a brown light source for its papers.
While brown/orange light offers greater visual comfort, a deep red light works just as well.

Choosing the right light bulb

A darkroom bulb must not emit any color tints that could fog the paper. A bulb sold as red may contain these undesirable color variations.

It is essential to choose a bulb specifically designed for darkroom use. Furthermore, even if the color is correct, the paper can still fog if the light is too strong. Therefore, it is important to select the correct wattage.