Electrical light sources. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Electrician

Electrical light sources. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Lighting

Electric light sources incandescent lamps, low pressure fluorescent lamps and high pressure mercury lamps.

The most common are electric incandescent lamps. The principle of their operation is based on the conversion of electrical energy passing through its thread into the energy of visible radiation that affects the organs of vision of a person and creates in him a feeling of light close to white.

This process occurs when the lamp filament is heated to 2600-2700 °C. The lamp filament does not burn out, since the melting point of the tungsten from which the filament is made is much higher (3200-3400 ° C) than the temperature of the filament incandescence, and also due to the fact that air is removed from the lamp bulb or the bulb is filled with inert gases (a mixture of nitrogen, argon , xenon), in which the metal is not oxidized.

The service life of incandescent lamps varies widely, since it depends on operating conditions, including the stability of the rated voltage, the presence or absence of mechanical influences on the lamp (shocks, vibrations), ambient temperature, etc. The average service life of general purpose incandescent lamps is 1000-1200 hours

During prolonged operation of an incandescent lamp, its filament, under the influence of a high heating temperature, gradually evaporates, decreases in diameter, and finally burns out.

The higher the heating temperature of the filament, the more light the lamp emits, but at the same time the process of evaporation of the filament proceeds more intensively and the lamp life is reduced. In this regard, for incandescent lamps, such a filament temperature is set at which the necessary light output of the lamp and a certain duration of its service are provided.

Vacuum are called incandescent lamps, from the internal volume (bulb) of which air is removed.

Lamps with flasks filled with inert gases are called gas-filled.

Gas-filled lamps, under equal conditions, have a greater light output than vacuum ones, since the gas in the bulb under pressure prevents the filament from evaporating, which makes it possible to increase its operating temperature. The disadvantage of gas-filled lamps is some additional heat loss in them from the filament through the convection of the gas filling the internal cavity of the bulb.

In order to reduce heat losses, gas-filled lamps are filled with gases with low thermal conductivity. Another way to reduce heat losses is to reduce the size and change the design of the filament: it is made in the form of a dense helical monocoil or double helix (bicoil).

The disadvantage of incandescent lamps is low light output: only 2-4% of the electrical energy they consume is converted into the energy of visible radiation perceived by the human eye; the rest of the energy is converted mainly into heat emitted by the lamp.

Widespread use in lighting electrical installations of enterprises, institutions, educational and medical institutions received fluorescent lamps, which is a hermetically sealed glass tube, the inner surface of which is covered with a thin layer of phosphor. Phosphors are chemical substances in which, under the influence of external factors (electric discharge, etc.), a glow, or luminescence, occurs. Air is removed from the tube and a small amount of gas (argon) and a certain amount of mercury are introduced. Inside the tube, in its glass legs, bispiral tungsten electrodes are fixed, connected to two-pin bases that serve to connect the lamp to the electrical network.

When voltage is applied to the lamp between its electrodes in mercury vapor, an electric discharge occurs, and the lamp begins to emit light. To provide a more intense emission of electrons, the electrodes of fluorescent lamps are coated with activating substances (oxides of strontium, barium or calcium).

The luminous flux emitted by fluorescent lamps is not the same in color.

Depending on the color of the luminous flux emitted by the lamp, there are:

fluorescent lamps (LD);
white light (LB);
cold white light (LHB);
warm white light (LTB), etc.

When performing work that requires accurate determination of color shades, for example, in a printing house in the manufacture of color reproductions, in an art workshop, in a textile or clothing factory, etc., LDI lamps are used for correct color reproduction.

Low pressure fluorescent lamps are gas-discharge electrical light sources.

Low-pressure fluorescent lamps are manufactured for a voltage of 127 V with a power of 15 and 20 W; for a voltage of 220 V with a power of 30, 40, 80 and 125 watts. The service life and normal operation of fluorescent lamps is about 5000 hours, provided that they are switched on infrequently, the rated voltage is stable and the ambient temperature is maintained at an optimum (15-25 ° C).

Widely used in modern lighting electrical installations of industrial enterprises are arc mercury lamps (DRL) high pressure. These lamps are available with two and four electrodes.

A four-electrode DRL consists of a threaded base, a flask (cylinder) and a quartz burner. Inside the burner is a certain amount of mercury and argon gas. Activated main and additional tungsten electrodes are soldered into the ends of the burner, and the inner surface of the flask is covered with a thin layer of phosphor.

When voltage is applied to the electrodes of the lamp in high-pressure mercury vapor, an electric discharge occurs, accompanied by an intense emission of light, in the spectrum of which there are no orange-red rays, which makes the lamp unsuitable for lighting, therefore the composition of the phosphor covering the inner surface of the bulb is selected so that under Under the influence of ultraviolet rays of the spectrum, it emits an orange-red color, which, mixing with the main luminous flux of the lamp, forms light that is perceived by the human eye as white with a slight greenish tinge.

Four-electrode DRLs differ from two-electrode ones in the presence of two additional electrodes connected to the main electrodes through additional resistances. This facilitates the ignition of the lamp: when voltage is applied to the lamp, a glow discharge occurs between the main and nearest additional electrodes, under the influence of which mercury vapor is ionized, contributing to the discharge between the main electrodes. DRL with a base with a diameter of 40 mm is produced with a power of 250-1000 watts.

Gas-discharge light sources (fluorescent lamps and DRL) are much more economical than incandescent lamps - their light output and service life are several times higher than the light output and service life of incandescent lamps.

Author: Bannikov E.A.

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