why is red the "safe light" in photography? why does it not damage the photo paper?

Answer 1

The original commercial Black & White were Orthographic and the safelight you mention was meant for Panographic Film.

The idea is that light rays visable generally range from red to yellow then green to blue on the basis of prismatic sensetivity. The problem is that ortho-film would turn anything red to black or near so. Such a pity because ortho film renders foliage and general shade better. As a result pan-films evolved as slightly de-sensetized for red which could now be seen as a soft grey. Ergo in the darkroon it is not that a red safelight will not expose film or paper, rather that the time it takes for a photo-sessetive reaction has been retarded or slowed down. The really great Darkroom Masters do in fact avoid safelights whenever possible and even when using one agitate their prints face down!

Answer 2

Hi,

In general, silver salts used on photographic paper are sensible to green, blue and ultraviolet ligh, so red light is used to as a safe light.

Red (1A) safelight filters are typically used for orthochromatic materials like litho film, certain liquid emulsions and some B&W photo papers. Never mix OC and red safelights in the darkroom -- even if a paper can be used with either safelight, the combination will usually cause fogging.

Answer 3

photo paper is orthochromatic. meaning it is not sensitive to red, orange, and yellow light. any of those colors of light can be used to handle photo paper safely for a limited time.