There are two sources of light, they are
- Natural lighting.
- Artificial lighting.
- Natural Light:
Natural lighting is the light given out by the natural elements in the environment such as that of sun and moon, Which again is reflected by the sky, water, earth, buildings and so on. Natural light is provided to interiors during day through the windows and sky light from ceiling and also the reflected light by the wall, floor, furniture and part of the light is also absorbed by the objects around. The light available will depend upon the amount of reflected light, which is dependant on the materials.
Sun is the first and the oldest source of light known to us. Its radiation not only permits us to see, but also allows the life supporting processes to take place. Sight is one of our senses dependent solely on an outside agency i.e., light for functioning through windows and ceiling.
A rough surface absorbs radiant energy more readily than a smooth one. Glass helps in diffusing the light as it distributes the light and provides more illumination at the farther side of the room. The use of shades and draperies also influence the amount of daylight that is available in a room. Opaque shades may cut out the light, while translucent shades transmit the light. Curtains and draperies may cut off as much as 75 percent of the light; where as a clear window and very thin curtain materials diffuse the light and soften the shadows. A window area equivalent to one-fourth of the floor area is desirable. It can be said that windows provide ventilation, light and decoration and thus satisfy three principal needs.
Thus, daylight is such an important factor that sufficient number of doors and windows are provided which also enhances the appearance of a room. As much daylight as is desired can now be procured by means of plain glass walls and large windows extending from floor to ceiling. Besides, movable curtains should be provided, so that the quantity of light can easily be controlled. Guidelines for good Natural Lighting:
- The interior surfaces of the walls should be painted with bright colors to reflect more light. The ceiling of a room should be, preferably, painted in white color to reflect more light.
- The corners of a room can be provided with windows to avoid dark corners. Broad openings give better distribution of light.
- Two opposite side openings give uniform light.
- Deep openings minimize glare.
- Windows should be provided with sunshades or other shading devices to eliminate glare of sunlight.
- Diffused glass gives more light than plain glass.
- Metal window sashes admit more light than wooden frames.
- Ventilators, at roof level, can be judiciously used in order to provide more light.
Artificial lighting is necessary during the nights and also when natural lighting is poor. Most of the interiors today are incomplete without artificial lighting. Wide varieties of lamps are used to enhance the design and appearance. The quantity and quality of light produced differs according to the type of lamp used.
Modern artificial light, particularly electric light is not only a remarkable functional utility, but also a marvelous flexible art medium. Artificial light may produce unity by its diffusion through the entire room. It may show contrast and emphasis by bringing bright light to important areas while subordinate areas remain in the shadows. It can bring rhythm and continuity to a room's furnishings by linking together the various points of emphasis.
Guidelines for good Artificial Lighting:
- Fluorescent lamps are more efficient than incandescent lamps. Fluorescent lamps produce 50 to 60 lumens per watt, where as incandescent lamps produce 10 to 17 lumens per watt. The life of fluorescent lamp is four times longer than the incandescent lamp.
- Luminaries should be located at a height of minimum 2.1 m above the floor level, except for some special reasons.
- The normal reflectance may be assumed for ceiling (white) as 0.7 watts (off white) as 0.5 watts and floor (grey) as 0.3 watts.
- Location of light points should be on longer walls.
- Periodic cleaning of luminaires is necessary to keep up their efficiency.
- Interior surfaces should be painted with bright colors for good surface reflection.
- General illumination in a room should satisfy the brightness ratio of 1: 10. The most important activity performed should be considered for deciding the illumination.
- The number of light points should be decided based on the floor area space and the importance of the activity performed. For example, in residences single linght point is sufficient upto 12 sq.m and two light points are required for floor area up to 22 sq.m.
- Glare of a luminaire can be reduced by use of dimmers or by using baffles, louvers or diffusers.