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The Effect of Light on Film


Film is commonly available as either daylight film for natural light and electronic flash, or tungsten film for artificial light.
Film is commonly available as either daylight film for natural light and electronic flash, or tungsten film for artificial light.

Light waves form into an image when passing through the camera’s lens. But, when light strikes the light-sensitive emulsion of film to make an exposure, it no longer acts as waves but as matter, making an impression on the film as a stream of particles called photons.

Photons physically change light-sensitive silver halides in film, forming an invisible, or latent, image, roughly proportional to the amount of light that struck the film. The film can then be developed, that is, chemically processed so a visible, permanent image is formed. This permanent image is made up of grains of metallic silver, clumped together in various densities based on the amount of light that struck them.


With negative film, the developed image is reversed in tone from the subject (the scene's bright areas are dark on the film, and the scene's dark areas are lighter), which is why it is called a negative.

The parts of the negative that received the most light will have the greatest density—more silver grains. Their density makes them more resistant to the passage of light through them during printing. So they will show up lighter on the print. And where the light was weakest, the accumulation of silver grains will be the least, allowing light to pass easiest through the negative, creating darker areas on the print.

Incandescent light is much warmer (more reddish-yellow) than natural daylight, requiring tungsten film - which is cooler (bluer) - to achieve a natural look.
Incandescent light is much warmer (more reddish-yellow) than natural daylight, requiring tungsten film - which is cooler (bluer) - to achieve a natural look.

Heat lamps provide extremely red light.
Heat lamps provide extremely red light.

THE TYPE OF LIGHT DETERMINES FILM CHOICE

Different light sources will affect film differently. Some films are made for use in daylight and others are specifically designed for artificial light sources.

Some light sources like high-intensity discharge lamps (sodium vapor, metal halide and mercury vapor lamps) are almost impossible to use with any film and still get good color rendition, although light-balancing filters can sometimes be used with these light sources with varying degrees of success.


Fluorescent light gives a greenish cast that is difficult to eliminate, even with filtration. Some daylight films, like Fuji Reala, make acceptable images in fluorescent lighting.
Fluorescent light gives a greenish cast that is difficult to eliminate, even with filtration. Some daylight films, like Fuji Reala, make acceptable images in fluorescent lighting.


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