مصادر الضوء المستخدمة في التصوير وخصائصها .. كتاب الإضاءة والفلم

Chapter two

Light sources used in photography and their properties

Light sources are divided into the following types:

1- Natural light sources: the sun during the day and the moon at night:

2- Electric light sources, which are:

(a) Tungsten lamps

(b) Electric arcs

(c) Vapor discharge lamps

(d) Fluorescent lamps

(e) Quartz Iodine Lamps

(f) Electronic flash tubes

3- Non-electrical sources:



(a) Flamming of gases from coal. Coal gases

(b) ignition of acetylene and x gas

(c) gas lamps.

(D) ignition of magnesium.

(e) Flashlights. flash bulbs

(f) Candle lights and matches.


daylight

The sun is the only source of illumination during the day in outdoor imaging, even if it is hidden behind the clouds. The amount of rays falling from it on the earth's surface during the summer at noon ranges around ten thousand feet | A candle, which is an amount equal to what we can get from four hundred Photoflood lamps that are six feet away from a specific object, and it is a light energy that is a thousand times more than what we get from the usual lighting inside our homes at night.

The amount of sunlight that reaches us varies from one month to another, as well as from one hour to another, due to the difference in the altitude of the sun from one month to another and from one hour to another.

If we investigated the accuracy of the expression, we would find that what is meant by the photographer is not sunlight, but rather daylight, so there is a difference between them. And the light reflected from the surfaces or neighboring spaces, whether they are green cultivated spaces, mountainous or sandy spaces, blue sea spaces, or even industrial spaces such as red, green or white buildings, for example.

The direct rays of the sun are white and travel, as we learned previously, in straight lines. As for the daylight, it is tinged with blue in relation to the sunlight, and it does not always come from above, but it may collide with any adjacent space first, then it is reflected from it, and it has lost its whiteness and is marred by a tinge of a certain color. Rather, the daylight must be reflected from the ground on which we are standing when photographing and be affected by its color as well. If it had been possible for the sun's rays to reach the earth without passing through strange circles that dispersed the light, this illumination would certainly lead to a strong contrast between the high lights and the shadows in the bodies upon which it falls, and it would be certain that you would see specific strong shadows. Very much, however, the sun's rays spread scattered when they collide with particles suspended in the atmosphere, whether from fog, clouds, dust or smoke. . . Etc., and this is something that would not only reduce the sharpness of the shadows that we see on objects and record them with photography, but also changes the light energy that reaches us, for example if a cloud passes in front of the sun when filming a movie, it is very likely that the exposure will change significantly between the first The snapshot and the last one, in fact there is research on this subject - that the amount of light falling may be reduced to one-tenth if a dense cloud falls in front of the sun, and this difference may occur within a range that does not exceed a few minutes.

In such cases, photography must continue under constant light conditions, because both the degree of image contrast and the correctness of its exposure are affected by the passage of such a cloud (1).