Classification of light sources. Part 2. Discharge lamps for high and low pressure

Classification of light sources. Part 1. Incandescent lamps and halogen lamps

Fluorescent lamps

Fluorescent lamps are low-pressure gas-discharge lamps in which, as a result of a gas discharge, ultraviolet radiation invisible to the human eye is converted into visible light by a phosphor coating.

Fluorescent lamps are a cylindrical tube with electrodes into which mercury vapor is pumped. Under the action of an electric discharge, the mercury vapor emits ultraviolet rays, which in turn cause the phosphor deposited on the walls of the tube to emit visible light.

Fluorescent lamps provide soft, uniform light, but the distribution of light in the space is difficult to control due to the large radiation surface. Linear, ring, U-shaped and compact fluorescent lamps differ in shape. Pipe diameters are often quoted in eighths of an inch (eg T5 = 5/8 « = 15.87 mm). In lamp catalogs, diameters are usually given in millimeters, for example 16 mm for T5 lamps.Most of the lamps are of international standard. The industry produces about 100 different standard sizes of general purpose fluorescent lamps. The most common lamps with a power of 15, 20.30 W for a voltage of 127 V and 40.80.125 W for a voltage of 220 V. The average duration of burning of the lamp is 10,000 hours.

The physical characteristics of fluorescent lamps depend on the ambient temperature. This is due to the characteristic temperature regime of the mercury vapor pressure in the lamp. At low temperatures, the pressure is low, so there are too few atoms that can participate in the radiation process. At too high a temperature, the high vapor pressure leads to an ever-increasing self-absorption of the UV radiation produced. At a flask wall temperature of approx. Lamps at 40 ° C achieve the maximum inductive spark discharge voltage and thus the highest light efficiency.

Advantages of fluorescent lamps:

1. High luminous efficiency, reaching 75 lm / W

2. Long service life, up to 10,000 hours for standard lamps.

3. The ability to have light sources of different spectral composition with better color rendering for most types of incandescent lamps

4. Relatively low (although creating glare) brightness, which in some cases is an advantage

The main disadvantages of fluorescent lamps:

1. Limited unit power and large dimensions for a given power

2. Relative complexity of inclusion

3. Impossibility of powering lamps with direct current

4. Dependence of the characteristics on the ambient temperature. For conventional fluorescent lamps, the optimum ambient temperature is 18-25 C.When the temperature deviates from the optimum, the luminous flux and the luminous efficiency are reduced. At temperatures below +10 C ignition is not guaranteed.

5. Periodic pulsations of their light flux with a frequency equal to the double frequency electric current. The human eye cannot notice these light oscillations due to visual inertia, but if the frequency of movement of the part matches the frequency of the light pulses, it can appear stationary or slowly rotate in the opposite direction due to a stroboscopic effect. Therefore, in industrial premises, fluorescent lamps must be switched on in different phases of the three-phase current (the pulsation of the light flux will be in different half-periods).

When marking fluorescent lamps, the following letters are used: L — fluorescent, D — daylight, B — white, HB — cold white, TB — warm white, C — improved light transmission, A — amalgam.

If you "twist" the tube of a fluorescent lamp into a spiral, you get a CFL - a compact fluorescent lamp. In their parameters, CFLs are close to linear fluorescent lamps (luminous efficiency up to 75 lm / W). They are primarily designed to replace incandescent lamps in a wide variety of applications.

Arc Mercury Lamps (DRL)

Marking: D — arc R — mercury L — lamp B — turns on without ballast

Arc Mercury Fluorescent Lamps (DRL)

Mercury-Quartz Fluorescent Lamps (DRLs) consist of a glass bulb coated with phosphor on the inside and a quartz tube placed inside the bulb that is filled with high-pressure mercury vapor. To maintain the stability of the properties of the phosphor, the glass bulb is filled with carbon dioxide.

Under the influence of ultraviolet radiation generated in the mercury-quartz tube, the phosphor glows, giving the light a certain bluish tint, distorting the true colors. To eliminate this drawback, special components are introduced into the composition of the phosphor, which partially correct the color; these lamps are called DRL lamps with chrominance correction. The life of the lamps is 7500 hours.

The industry produces lamps with a capacity of 80,125,250,400,700,1000 and 2000 W with a luminous flux from 3200 to 50,000 lm.

Advantages of DRL lamps:

1. High luminous efficiency (up to 55 lm / W)

2. Long service life (10000 hours)

3. Compactness

4. Not critical for environmental conditions (except very low temperatures)

Disadvantages of DRL lamps:

1. The predominance of the blue-green part in the spectrum of rays, which leads to unsatisfactory color rendering, which excludes the use of lamps in cases where the objects of discrimination are human faces or painted surfaces

2. Ability to operate on alternating current only

3. The need to turn on through a ballast choke

4. Duration of ignition when switched on (about 7 minutes) and the start of re-ignition after even a very short interruption of the power supply to the lamp only after cooling (about 10 minutes)

5. Pulsating luminous flux, greater than that of fluorescent lamps

6. Significant reduction in light flux towards the end of the service

Metal halide lamps

Arc metal halide lamps (DRI, MGL, HMI, HTI)

Marking: D — arc, R — mercury, I — iodide.

Metal halide lamps -these are high-pressure mercury lamps with additions of metal iodides or rare earth iodides (dysprosium (Dy), holmium (Ho) and thulium (Tm), as well as complex compounds with cesium (Cs) and tin halides (Sn). These compounds decompose in the central discharge arc and the metal vapors can stimulate the emission of light whose intensity and spectral distribution depend on the vapor pressure of the metal halides.

Externally, metallogenic lamps differ from DRL lamps in the absence of phosphor on the bulb. They are characterized by high luminous efficiency (up to 100 lm / W) and a significantly better spectral composition of the light, but their service life is significantly shorter than that of DRL lamps, and the switching scheme is more complicated, since in addition to ballast choke, contains an ignition device.

Frequent short-term switching on of high-pressure lamps will shorten their service life. This applies to both cold and hot starts.

The luminous flux practically does not depend on the temperature of the environment (outside the light fixture). At low ambient temperatures (up to -50 ° C) special ignition devices must be used.

HMI lamps

HTI short-arc lamps — metal halide lamps with increased wall load and very short distance between electrodes have even higher light efficiency and color rendering, which, however, limits their life. The main application area of ​​HMI lamps is stage lighting, endoscopy, cinema and daylight shooting (color temperature = 6000 K). The power of these lamps varies from 200 W to 18 kW.

HTI short-arc metal halide lamps with small interelectrode distances have been developed for optical purposes. They are very bright. Therefore, they are primarily used for lighting effects, such as positional light sources and in endoscopy.

High pressure sodium (HPS) lamps

Marking: D — arc; Na — sodium; T — tubular.

High-pressure sodium lamps (HPS) are one of the most efficient groups of visible radiation sources: they have the highest luminous efficiency among all known gas discharge lamps (100-130 lm / W) and a slight reduction in luminous flux with a long service life . In these lamps, a discharge tube made of polycrystalline aluminum is placed inside a cylindrical glass flask, which is inert to sodium vapor and transmits its radiation well. The pressure in the pipe is about 200 kPa. Duration of work — 10-15 thousand hours. The extremely yellow light and the correspondingly low color rendering index (Ra = 25) allow them to be used in rooms where there are people, only in combination with other types of lamps.

Xenon lamps (DKst)

DKstT arc xenon tube lamps with low luminous efficiency and limited service life are distinguished by the spectral composition of light closest to natural daylight and the highest unit power of all light sources. The first advantage is practically not used, since the lamps are not used inside buildings, the second determines their wide use for lighting large open spaces when mounted on high masts. The disadvantages of the lamps are very large pulsations of the light flux, an excess in the spectrum of ultraviolet rays and the complexity of the ignition circuit.