The following points highlight the four main factors to be considered while selecting lamps. The factors are: 1. Fitting Required for Filament Lamp 2. Lamp Connection Caps 3. Reflectors 4. Diffusers.
Factor # 1. Fitting Required for Filament Lamp:
Light fitting should be made of cold rolled annealed steel sheets duly oiled and picked against rust. Fitting for outdoor use should be preferably cast aluminium which has a better resistance than commercial quality aluminium. The fitting must be simple in design and easily cleaned.
The requirements of most of the installation can be met by one of the following types of fittings:
a. Standard Reflectors:
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These reflectors are made to accommodate lamps of ratings from 100 to 1500 W and designed in such a manner that they give adequate and uniform illumination when they are mounted on working plane.
b. Diffusion Fittings:
When more diffused light is required, a diffusing glass screen may be fixed across a standard type of reflector. This type of fitting is used where highly polished articles are dealt with.
c. Concentrating Reflectors:
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A reflector with a concentrated beam is employed in large machine shops and foundries, where fittings are to be mounted on considerable height above the working plane.
d. Angle Reflectors:
Angle reflectors are used to provide illumination in a vertical plane where concentrating type reflectors are used. These can be mounted on a wall at a suitable place.
Factor # 2. Lamp Connection Caps:
For easy screw in mounting of lamps to lamp-holders various types of caps are provided in lamps as below:
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1. Bayonet Capped (B.C.)
2. Screw type
The caps may be further 2 pins or 3 pins type. 3 pin type caps are designed for mounting of mercury or sodium vapour lamps because they are started at lower voltage.
Factor # 3. Reflectors:
Fitting can have following optical features:
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(a) Reflectors:
(i) Dispersive type
(ii) Mirror
(b) Diffusers:
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(i) Transluscent
(ii) Frosted (Opaque)
(iii) Diffused coating
(c) Reflector cum diffuses
1. Dispersing Type Reflectors:
Here the reflecting surface is either white stone enamelled or vitreous enamelled. Vitreous enamelled are more expensive and less efficient optically but are more suitable for use in damp and corrosive atmosphere.
2. Mirror Type Reflectors:
Mirror type reflectors have highly polished surface for specular reflection. Chromium plated, silvered glass, copper sheets are typical examples of this. These reflectors have narrow medium and wide beam applications and are used in yard lighting luminaires.
3. Polished Metallic Reflectors:
These are provided in asymmetric fittings to make their lighting pattern symmetrical and to provide intense beam of light. These are having nickel plated metallic surfaces used in flood lighting.
Factor # 4. Diffusers:
These are in various decorative shapes like spherical, cylindrical and made of frosted glass plyster, plastic transparent sheets are made by U.K.
The diffuser for fluorescent luminaires can be made of continuous opal acrylic diffuser. Continuous acrylic diffusers have less efficiency but have very uniform and diffused reflection of light which has very high soothing effect on eyes.