Focus on thermal testing of lamps from the perspective of radiant energy analysis of light sources

Light is a form of energy that can travel from one object to another without any other medium. This transfer of energy is called radiation, which means that energy travels in all directions in a straight line from the source, although in reality it does not always travel in a straight line, especially when passing through an object. Some forms of radiation are composed of particles, such as radiation caused by radioactive substances. Light was once thought to be a beam of particles, but later it was proved that it is more appropriate to describe the characteristics of light as waves, and the direction of the light is also the direction of wave propagation. About 100 years ago, people confirmed that the nature of light is electromagnetic waves, and later they found that visible light waves only account for a very small part of the extremely wide range of electromagnetic waves.

The wavelength range of the visible light part of the electromagnetic wave is about 380nm~780nm. Various wavelengths within this range can be distinguished by the color perception of the eyes. Blue and purple belong to short waves, red belongs to long waves, and yellow and green are in the middle part of the visible wavelength range.

Electromagnetic radiation with wavelengths beyond the violet and red ends of the visible spectrum is called ultraviolet radiation and infrared radiation, respectively.

The radiation energy of a light source refers to the energy of the light radiated by the light source, including ultraviolet radiation energy, visible light radiation energy and infrared radiation energy. Energy other than radiation is non-radiative loss, including conduction and convection loss.

1. Analysis of radiation energy of light source

1. Energy analysis of incandescent lamps

The energy output of some incandescent lamps in terms of visible radiation, infrared radiation, conduction and convection losses is shown in Table 1.

Table 1 Energy output of some incandescent lamps

As can be seen from Table 1, taking a 100W incandescent lamp as an example, the proportion of visible light radiation energy is 10.0%. The proportion of infrared radiation energy is 72.0%. The proportion of energy radiated in the form of light is 82.0%. Conduction and convection losses account for 18%.

The non-radiative losses of incandescent lamps include absorption losses of the bulb shell and lamp holder, gas losses, and heat losses from the bracket.

The energy distribution of visible light radiation, infrared radiation and non-radiative heat loss of vacuum incandescent lamps, single-helix and double-helix gas-filled incandescent lamps is shown in Table 2.

As can be seen from Table 2, most of the power of incandescent lamps is converted into infrared radiation, and the proportion of visible light radiation power is very small, generally less than 10%. Infrared radiation accounts for 67%~87%.

An example of an energy balance for a 100W general lighting bulb (GLS) is shown in Figure 1.

1. Visible light radiation 5W; 2. Infrared radiation from the filament 61W;

3. Conduction and convection losses from the filament to the bulb wall are 34W; 4. Infrared radiation from the bulb shell is 22W;

5. Total conduction and convection losses 12W; 6. Total infrared radiation 83W.

Figure 1 Energy balance of a 100W GLS lamp

As can be seen from Figure 1, for the 100W GLS example, visible light radiation accounts for only 5%, infrared radiation accounts for 83%, and conduction and convection losses account for 12%.

In general, forward infrared radiation accounts for the vast majority of the energy of incandescent lamps, a large amount of energy is used for forward heat generation, and only a small part of the energy is used for forward light emission.

It can be seen from Table 4 that for a 400W high-pressure mercury lamp, visible light radiation accounts for 17.5%-20%, infrared radiation accounts for 15%, and heat loss accounts for 80%-82.5%.

The energy balance of visible light radiation, infrared radiation, conduction and convection loss of a 100W ultra-high performance light source is shown in Table 5.

As can be seen from Table 5, for a 100W UHP lamp, visible light radiation accounts for 25%, infrared radiation accounts for 34%, and conduction and convection losses account for 11%.

The visible light radiation, infrared radiation, electrode loss, gas heat loss and absorbed energy balance of a 400W high pressure sodium lamp are shown in Table 6.

It can be seen from Table 6 that for various types of 400W high pressure sodium lamps, visible light radiation accounts for 25%-36% and infrared radiation accounts for 20%-30%.

The energy balance of visible light radiation, infrared radiation, non-radiation, etc. of 500W sodium-thallium-indium lamp and high-pressure mercury lamp is shown in Table 7.

It can be seen from Table 7 that for a 500W sodium-thallium-indium lamp, visible light radiation accounts for 24%, infrared radiation accounts for 30.2%, ultraviolet radiation accounts for 8.8%, and the non-radiative part accounts for 37%; for a 500W high-pressure mercury lamp, visible light radiation accounts for 14.6%, infrared radiation accounts for 15%, ultraviolet radiation accounts for 22.4%, absorbed radiation accounts for 22%, and the non-radiative part accounts for 22%.

The energy balance of visible light radiation, infrared radiation, ultraviolet radiation and non-radiative radiation of a 400W sodium-thallium-indium lamp is shown in Table 8.

It can be seen from Table 8 that for a 400W sodium-thallium-indium lamp, visible light radiation accounts for 23.9%, infrared radiation accounts for 37.0%, ultraviolet radiation accounts for 3.1%, and the non-radiative part accounts for 36%; for a 400W high-pressure mercury lamp, visible light radiation accounts for 15.2%, infrared radiation accounts for 14.3%, ultraviolet radiation accounts for 1.8%, and the non-radiative part accounts for 68.7%.

An example of the energy balance of a 400W high pressure mercury lamp with a transparent glass bulb is shown in FIG3 .

1. Discharge positive column power 360W; 2. Electrode heat loss 40W; 3. Visible light radiation 50W;

3. Ultraviolet radiation from the discharge positive column 90W; 5. Infrared radiation from the discharge positive column 60W;

6. Heat loss of discharge positive column 160W; 7. Ultraviolet radiation 10W; 8. Infrared radiation 80W;

9. Total infrared radiation 260W; 10. Conduction and convection 80W.

Figure 3 Energy balance of a 400W transparent glass high pressure mercury lamp

As can be seen from Figure 3, for a 400W high-pressure mercury lamp with a transparent glass shell, visible light radiation accounts for 12.5%, ultraviolet radiation accounts for 2.5%, infrared radiation accounts for 65%, and conduction and convection account for 20%.

An example of the energy balance of a 400W high pressure mercury lamp with a phosphor coated glass bulb is shown in Figure 4.

1. Discharge positive column power 370W; 2. Electrode heat loss 30W; 3. Visible light radiation from discharge positive column 59W;

4. Ultraviolet radiation from the discharge positive column is 73W; 5. Infrared radiation from the discharge positive column is 60W;

6. Heat loss of discharge positive column 178W; 7. Visible light radiation from phosphor layer 8W;

8. Ultraviolet radiation 15W; 9. Infrared radiation 50W; 10. Total visible light radiation 67W; 11. Total infrared radiation 226W; 12. Conduction and convection 92W.

Figure 4 Energy balance of a 400W high pressure mercury lamp with a phosphor-coated glass bulb

As can be seen from Figure 4, for a 400W high-pressure mercury lamp with a phosphor-coated glass shell, visible light radiation accounts for 16.8%, ultraviolet radiation accounts for 3.7%, infrared radiation accounts for 56.5%, and conduction and convection account for 23%.

An example of the energy balance for a 160W self-ballasted high pressure sodium lamp is shown in Figure 5.

1. Discharge tube power 50W; 2. Filament power 110W; 3. Discharge positive column power 24W; 4. Electrode heat loss 26W;

5. Infrared radiation from the filament 37W; 6. Conduction and convection losses 67.5W;

7. Visible light radiation from the filament 5.5W; 8. Visible light radiation from the discharge 7.5W;

9. Ultraviolet radiation from discharge 9W; 10. Infrared radiation from discharge 7.5W;

11. Visible light radiation from the phosphor layer is 1.5W; 12. Infrared radiation is 7W;

13. Total infrared radiation from discharge plus filament 70.5W; 14. Total visible light radiation 14.5W;

15. UV radiation 0.5W; 16. Total infrared plus conduction and convection 145W.

Figure 5 Energy balance of 160W self-ballasted high pressure sodium lamp

As can be seen from Figure 5, for a 160W self-ballasted high-pressure sodium lamp, visible light radiation accounts for 9.1%, ultraviolet radiation accounts for 0.3%, infrared radiation accounts for 48.4%, and conduction and convection account for 42.2%.

An example of the energy balance for a typical three spectrum metal halide lamp is shown in Figure 6.

1. Discharge positive column power 364W; 2. Electrode heat loss 36W; 3. Visible light radiation 97W;

4. Ultraviolet radiation from discharge 15W; 5. Infrared radiation from discharge 98W;

6. Heat loss of discharge positive column 154W; 7. Ultraviolet radiation 5W; 8. Infrared radiation 10W;

9. Total infrared radiation 237W; 10. Conduction and convection 61W.

Figure 6 Typical energy balance of three spectrum metal halide lamps

As can be seen from Figure 6, for a typical 400W metal halide lamp with three spectra, visible light radiation accounts for 24.25%, ultraviolet radiation accounts for 1.25%, infrared radiation accounts for 59.25%, and conduction and convection account for 15.25%.

An example of the energy balance for a 180W low pressure sodium lamp is shown in Figure 7.

As can be seen from Figure 7, for a 180W low-pressure sodium lamp, visible light radiation accounts for 35%, infrared radiation accounts for 34.5%, and conduction and convection account for 30.5%.

An example of the energy balance for a 400W high pressure sodium lamp is shown in Figure 8.

1. Discharge positive column power 376W; 2. Electrode heat loss 24W; 3. Visible light radiation 118W; 4. Ultraviolet radiation 2W;

5. Infrared radiation 80W; 6. Heat loss of discharge positive column 176W; 7. Ultraviolet radiation 1W; 8. Infrared radiation 1W;

9. Total infrared radiation 221W; 10. Conduction and convection 60W.

Figure 8 Energy balance of 400W high pressure sodium lamp

As can be seen from Figure 8, for a 400W high pressure sodium lamp, visible light radiation accounts for 29.5%, ultraviolet radiation accounts for 0.25%, infrared radiation accounts for 55.25%, and conduction and convection account for 15%.

In general, high-pressure mercury lamps account for 14.3% to 65% of infrared radiation, and conduction and convection account for 20% to 68.7%. High-pressure sodium lamps account for 20% to 55.25% of infrared radiation, and conduction and convection account for 15% to 42.2%. Metal halide lamps account for 30.2% to 59.25% of infrared radiation, and conduction and convection account for 15.25% to 37%. Low-pressure sodium lamps account for 34.5% of infrared radiation, and conduction and convection account for 30.5%.

1. Energy analysis of LED

LED has 25%-30% visible light, no infrared radiation, and 70%-75% heat (non-radiant heat). The visible light that LED shines forward is only 25%-30%, and no infrared comes out. The rest is heat, not radiant heat, but conducted heat.

According to the analysis of the radiation energy of various light sources, the primary and secondary relationships of the energy corresponding to various light sources are obtained as shown in Table 9.

2. The measurement points of the objects illuminated by the spotlight that should be paid attention to during the thermal test of lamps and lanterns China Lighting Network Technical Paper·Electric Light Source

For incandescent lamps, reflective incandescent lamps are of great interest because of their strong light-collecting properties. General reflective bulbs use a parabolic reflector, and there is also a reflective incandescent lamp with an ellipsoidal reflector. Commonly used are aluminum-plated parabolic reflector lamps (PAR lamps) and multilayer dielectric film reflector lamps (MR lamps). PAR lamps are divided into two categories: spotlight and floodlight, with a beam angle of 5º~60º. RF is a floodlight reflector, RS is a spotlight reflector, BRF is a closed spotlight reflector, and BRS is a closed spotlight reflector. Reflective incandescent lamps can be divided into two categories: blown bulb reflector incandescent lamps and pressed bulb reflector incandescent lamps according to the processing method of the bulb. PAR lamps use a pressed bulb closed beam lamp structure. In order to reduce the heat of the emitted light, an infrared reflective film is applied to the lens to make a cold light PAR lamp. MR halogen tungsten lamps are halogen tungsten lamps that integrate the reflector and the bulb. The parabolic reflector is made of pressed glass, and the inner surface is coated with a multi-layer dielectric film. The film reflects visible light and transmits infrared light. The visible light is reflected to the object to be illuminated, and most of the infrared light emitted is filtered out through the reflector. There is almost no infrared radiation in the light received by the target, so the MR halogen lamp is also commonly known as the cold beam halogen lamp. The MR halogen lamp can be made into three types of wide, medium and narrow beam models.

Reflective incandescent lamps can be divided into those with heat directed forward and those with heat directed backward. Reflective incandescent lamps with heat directed forward are those with heat and light emitted in the same direction, also known as general reflective lamps. Reflective incandescent lamps with heat directed backward are those with heat and light emitted in opposite directions. Reflective incandescent lamps with heat directed forward and those with heat directed backward may have the same shape, so care should be taken to prevent misuse.

If a reflective incandescent lamp with heat dissipating backwards is used in a reflective incandescent lamp with heat dissipating forwards, the temperature of the lamp holder, wires, lampshade, etc. may exceed the specified value, which may cause danger. If such a dangerous situation exists, 3.2.11 of GB 7000.1 requires that the lamp be marked with the symbol

, to warn that cold beam lights cannot be used.

When using a reflective incandescent lamp that emits heat backwards, the temperature of the illuminated object may exceed the specified value, which may cause a fire hazard. If such a dangerous situation exists, 3.2.15 of GB 7000.1 requires that the lamp be marked with the symbol

, to inform users that the lamp is designed to use a bowl-shaped mirror reflector bulb.

For incandescent lamps, especially reflective incandescent lamps that emit heat forward, attention should be paid to the temperature measurement point of the illuminated object.

For HID lamps and low-pressure sodium lamps, attention should be paid to the temperature measurement point of the illuminated object.

As can be seen from Table 9, 3.2.13 of GB 7000.1 requires that the symbol of the shortest distance from the illuminated object to the lamp mark

, not applicable to LED light sources. The focus of thermal testing of LED lamps is not the forward radiant heat, but the backward conductive heat.

3. Conclusion

The measurement point of the object illuminated by the spotlight that should be paid attention to during the thermal test of the lamp depends on the analysis of the radiation energy of various light sources. Not all light sources need to measure the temperature of the illuminated surface. LED lamps do not need to measure the temperature of the forward illuminated surface.