Why do they use red lights for photography?

Answer 1

Red, or more often amber filtered lamps of low wattage are used in print darkrooms because the photo sensitive materials used in printing are usually not sensitive to red or amber (red/orange) light. These lights are called "safe" lights, and allow the printer to see as s/he works. (There are some photographic films, notably x-ray films, which are also not red sensitive and may be developed under red safelight.)

The earliest photosensitive materials were "monochromatic," meaning that they were sensitive only to one color of light, which was blue. They were green and red "blind." Later, the addition of certain chemicals to the emulsions made them "orthochromatic;" sensitive to both green and blue, but still not to red light. This characteristic allowed early photographers to use red filters over their windows or in their "dark tents" in the field so they could see what they were doing. Eventually, the inventors added still more chemicals to the emulsions to make them "panchromatic;" that is, sensitive to all colors of light, which remains true for most negative materials and all color emulsions to the present day. These must for the most part be handled in total darkness, but it's not such a challenge as you might think. Just imagine being blind. Blind people do very well in total darkness all their lives.

But since most black and white printing papers do not need to be either very fast or sensitive to red light, a reddish or orange color safe light may be used to make life easier in the print room. When the multigrade printing papers were introduced in the 1970's, the sensitivity shifted and the safelights had to be both dimmer and a more orange color to avoid fogging the paper.

A tip: If you're setting up a print room, know that there is no such thing as a truly "safe" light. Any safelight will fog your paper if it's too close or the wrong color, and safelight filters fade with time and can degrade your images without your noticing. Never expose paper to safelight except when you are ready to use it. Limit the exposure of the remaining paper to safelight. Keep it in its original package or in a special box called a "paper safe." A popular test for safelight "safety" is to make a print exposure (an initial exposure to white light from the enlarger is necessary to hypersensitize the paper). Place the sheet of exposed paper on the bench near your developer tray and cover most of it with an opaque card. With the safelights turned on, slide the card down the exposed print at timed intervals of up to, say, five minutes, then develop the sheet in total darkness. When the test sheet is in the fixer you can look at it in white light. If you see anystriping across the image where the paper was uncovered, you are getting safelight fogging at that interval and may need to reduce the wattage, change the filters, move the safelights further from the paper, or all of the above. You may not get fogging at one minute but it may show up at two or three minutes. I used to insist on absolute safety for a safelight exposure of up to five minutes since I developed my papers always for three full minutes.

Answer 2

I presume you mean outdoors, as daylight can also be present indoors.

It is used for fill-lighting, which is meant to "fill in" shadows without becoming the predominant source of light. This means it has to be balanced, which can be achieved easily through experimentation, note taking, and practice. An incident light meter might help, but is not really necessary.

To better understand why it is used, have someone stand in the shade of a tree without a hat on (a hat brim will diminish this experiment's results). Notice the level of light around their eye sockets. Now hold a sheet of cardboard (about 2 feet by 2 feet that you've cut from a box) and hold it just above their head. Position it as though it were a hat brim; that is to say, it should extend out in front of their head but above their head. Now look at their eye sockets and you will see they are lighter. Remove/replace the sheet several times as you watch . When the sheet is above their head, the main light becomes frontal, as opposed to before when it was coming from the sky. Frontal light makes a more pleasing outdoor portrait, and it is why a professional wedding photographer will use frontal flash outdoors. This effect can be achieved and better controlled with reflectors and canopies, but that is not for the rapid pace of wedding and other outdoor portraiture.

Answer 3

They're usually amber. The reason they're used for printing black & white photographs (film is developed in total darkness) is that black & white paper is not very sensitive to that color of light. If subjected to red/amber for too long, or if the light is too close for the wattage used, it will fog the paper. Some early black and white papers could be developed under green safelights, but it is not likely that there is much (if any) use for this type of paper anymore. If you use a colored light at the right strength and distance that is compatible with your paper, you can work under light without fogging your pictures.

Answer 4

Sounds hard but I know this one.

So the picture looks good and lightly because they have the light things and they need it dark so it looks good.

Answer 5

The photographic film used is not sensitive to the red light so it does not affect the picture taken.