Light in electrical sources can be produced in two basic ways:
— by heating suitable solids to a high temperature,
— by causing luminescent radiation.
Electric light sources are divided into the following groups:
a) lamps with temperature generation of light - incandescent lamps;
b) lamps with luminescent light production:
— fluorescent lamps — fluorescent lamps,
- discharge lamps: fluorescent, mercury, sodium,
c) lamps with mixed light production - mercury-incandescent lamps.
The basic parameters characterizing light sources are: luminous flux, durability and luminous efficiency. In addition, light sources are characterized by a color temperature and a color rendering index.
The color temperature of a light source is the temperature of the black body, in which it emits radiation of the same chromaticity as that of the considered source.
Color (chromaticity) light of a given source can therefore be determined by the corresponding blackbody temperature. The color temperature of light bulbs ranges from 2500 K do 3250 K, while the color temperatures of discharge sources range from 2100 K do 6500 K.
Another feature of light sources is the ability to render colors. This feature is determined by the color rendering index. The maximum possible value of the color rendering index Ra is 100. The higher the Ra index, the greater the color rendering accuracy. The bulbs are characterized by the highest value of the color rendering index (Ra = 100), the smallest sodium discharge lamps (Ra = 20).
Light sources are characterized by a constant power consumption, and their unit capacities are small. Most light sources work with a power factor equal to 1 or close to oneness. The disadvantageous feature of electric light sources is the simultaneous load of the network and the power plant caused by them. It is especially unfavorable in winter, when the load caused by lighting consumers is superimposed on that caused by other consumers (mainly industrial), leading to load peaks.