Fluorescent lamps. Construction principle. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Fluorescent lamps. Construction principle. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Fluorescent lamps

Fluorescent Lamp (low pressure mercury lamp; hereinafter - LL) is a gas-discharge light source (Fig. 2.1 and 2.2). Structurally, it is a glass tube with a layer of phosphor deposited on the inner surface. Tungsten spiral electrodes are introduced into the ends of the tube. To increase the emissivity, an oxide suspension is applied to the electrodes, made from carbonates or peroxides of alkaline earth metals.

Inside the lamp rarefied mercury vapor and an inert gas (argon) are found. The pressure of mercury vapor in the LL depends on the temperature of the walls of the lamp and at a normal operating temperature of 40 ° C is approximately 0,13-1,3 N / m2 (10 - 2 - 10 - 3 mm Hg).

Such a low pressure provides intense discharge radiation in the ultraviolet region of the spectrum (mainly with a wavelength of 184,9 and 253,7 nm). Under the action of an electric voltage (field) applied to the electrodes, a gas discharge occurs in the lamp.

Fluorescent lamps. Construction principle
Rice. 2.1. Modern fluorescent lamps

In this case, the current passing through the mercury vapor causes ultraviolet radiation. A layer of a special substance is deposited on the inner surface of the lamp (phosphor). The most common phosphor is calcium halophosphate activated with antimony and manganese.

Fluorescent lamps. Construction principle
Rice. 2.2. The structure of a fluorescent lamp

By changing the ratio of activators, it is possible to obtain phosphors of different brands and produce lamps of different colors.

Ultraviolet radiation, acting on the phosphor, makes it glow, i.e., the phosphor converts the ultraviolet radiation of the gas discharge into visible light. The glass from which the LL is made prevents the output of ultraviolet radiation from the lamp, thereby protecting our eyes from radiation harmful to them.

The exceptions are bactericidal and ultraviolet lamps; in their manufacture, uviolet or quartz glass is used, which transmits ultraviolet light.

Today LL with amalgams of In, Cd and other elements are widely used. The lower mercury vapor pressure above the amalgam makes it possible to extend the temperature range of optimal light outputs to 60°C instead of 18-25°C for pure mercury.

When the ambient temperature rises above the permissible norm (25 °C for pure mercury and 60 °C for amalgams), the wall temperature and mercury vapor pressure increase, and the luminous flux decreases.

Even more noticeable decrease in luminous flux observed with a decrease in temperature, and, hence, the pressure of mercury vapor. At the same time, the ignition of the lamps also deteriorates sharply, which makes it impossible to use them at temperatures below -10 ° C without warming devices.

In this regard, it is of interest mercury-free LL with low pressure discharge in inert gases. In this case, the phosphor is excited by radiation with a wavelength of 58,4 to 147 nm. Since the gas pressure in mercury-free LLs is practically independent of the ambient temperature, their light characteristics also remain unchanged.

Today the problem of LL operation at low temperatures is solved:

using LL of a new generation of T5 lamps (with a tube diameter of 16 mm);
using compact fluorescent lamps;
LL powered by high-frequency electronic ballasts (electronic ballast).

Light output LL increases with an increase in size (length) due to a decrease in the proportion of anode-cathode losses in the total luminous flux. That's why more rational use one 36W lamp than two 18W lamps.

LL service life limited to deactivation and sputtering (depletion) of cathodes. Fluctuations in the mains voltage and frequent switching on and off of the lamps also negatively affect the service life. When using electronic ballasts, these factors are minimized.

Author: Koryakin-Chernyak S.L.

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