الإضاءة غير المركزة .. كتاب الإضاءة والفلم

Second: unfocused lighting

We obtain this type of lighting by means of reflectors (Fig. 26), which differ from concentrated lighting in that the latter leads to a very high contrast in lighting, while the searchlights lead to a lower contrast, and a third middle area appears in the image between the areas of high illumination and areas of Shadows are intermediate in intensity between the two.

Tungsten lamps are often the source of radiation in searchlights designed for unfocused lighting, and behind the lamp there is a reflector, whose function is not limited to merely directing and collecting light in one specific direction, but also intensifies the light coming out of the lamp.

The shape of the reflector has a direct effect on the properties of the rays reflected from it. The reflector with a wide diameter emits less focused and softer rays than the narrow, deep reflector (Fig. 26). The reflector, which is highly polished from the inside or reflects the rays with a concave mirror, comes out. Specnlar rays are closer to focus than what comes out of unpolished Max. The location of the lamp in front of the reflector greatly affects the shape of the rays as well. If the lamp falls into the focus of the reflector, the rays will come out parallel, and the angle of exit of the rays will widen when the lamp is brought close to the reflector, so the rays will become softer (Fig. 27). The extent of the reflector curvature also affects the degree of scattering or gathering of the rays (Fig. 28).

We have previously mentioned, in connection with the discussion of the tungsten lamp, that the size of the lamp on the one hand, and the area of ​​the resistance wire (filament) in the lamp on the other hand, has an effect on the softness of the light, as large, opaque white lamps lead to a softer light, as well. The softness of the rays increases and their concentration decreases with the expansion of the diameter of the lamp filament.

There are reflectors that accommodate more than one lamp, and the number of lamps may increase to twelve (Fig. 29). Such a reflector may be made of aluminum or painted with a lustrous coating similar to aluminium, or painted with a matte white coating and used as general and widespread illumination, usually overhead. The lamps may be exposed or covered with opaque white opal glass or light gauze to increase the distribution of light, and the reflector may have a tortuous surface.

We summarize the following factors that would increase the softness and distribution of rays:

(a) The uncoated inner surface of the reflector increases the light distribution.

(b) The closer the lamp is to the reflector, the greater the distribution of light.

(c) The greater the area of ​​the reflector, the greater the distribution of light.

(d) The larger the size of the lamp filament, the greater the distribution of light.

(e) White, opaque opal glass lamps help distribute light.

(f) It is possible to increase the softness and distribution of illumination by placing an object in front of the path of the rays exiting from the source, so the angle of the rays exit will widen and the distribution and softness will increase. This body may be a piece of white cloth, gauze, blotting paper, or a metal wire placed directly in front of the lamp to block its direct rays, so the rays come out from around it.