Chapter 27, Problem 4Q

To determine

Why red bulb sometimes used for developing black and white film in darkrooms?

Answer to Problem 4Q

Solution:

Black and white films are very low sensitive to the red.

Explanation of Solution

Red bulb used for black and white photography where the paper is not sensitive to the red wavelengths of light and it allows you to see enough to position the paper on the enlarger and do your other work.

We can't use red light when you're putting film in a tank (the tanks themselves are light tight)and it can't be used with color paper which needs to be sensitive to all the wavelengths.