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effect of structural materials on the thermal performance of led Fluorescent tube lamp and led bulb

Ben Wang through experimental research, comparative analysis of the current market typical LED Fluorescent tube Lamp and LED bulb light and heat performance, all-glass LED Fluorescent tube Lamp in the light measurement parameters on the best performance of all plastic LED Fluorescent tube Lamp color coordinate stability the best. Different arrangement of the chip affect the LED bulb light measurement and color coordinate stability.

LED Fluorescent tube Lamp and LED bulb as a typical LED light source, has been widely used. Structure and materials will have an impact on its performance. On the fluorescent lamp, lamp material not only affects the luminous parameters of lamps, but also affect the reliability. The chip layout on the bulb lamp substrate will also have some impact on the light color parameters. White LED light source of the electro-optical conversion efficiency is generally about 30%, most of the electricity
Can be converted into heat, heat transfer through the substrate to the heat sink, through the surface of the air convection heat dissipation device. Thermal efficiency of fluorescent or bulb lamp light efficiency and service life. In this paper, the effects of structure and materials on the light, color and thermal performance of LED Fluorescent tube Lamp and LED bulb lamp are compared and analyzed.

Fluorescent lamp

1.1 The impact of color temperature on optical properties

Song Guohua, etc. studied the LED color temperature, luminous efficiency, color rendering index relationship. The experimental results shown in Figure 1. Can be seen, white LED color temperature is greater than 4000K, with the color temperature increases, the luminous efficiency showed a slow downward trend, while the color rendering index is on the rise. Experiments on the same model of three different color temperature of the LED Fluorescent tube Lamp (NVC3000K, NVC4000K, NVC6000K) for testing, the results shown in Table 1, verify the trend.

The color rendering of the light source depends on its spectral power distribution, and the continuous spectrum light source has a good color rendering property. The increase of color rendering index is accompanied by the decrease of luminous efficiency, and also shows that the color temperature indirectly affects the luminous efficiency of LED Fluorescent tube Lamps.

1.2 The structure of the optical properties

LED Fluorescent tube Lamp structure shown in Figure 2.

LED Fluorescent tube Lamp shell of the role of the main protection, positioning, connecting components, heat, optimize lighting effects. Lamps include: all-plastic, all-glass, semi-plastic semi-aluminum structure. The T8LED Fluorescent tube Lamps were tested with T8LED Fluorescent tube Lamp, and the influence of the structure on the optical performance of LED Fluorescent tube Lamp was discussed. Semi-plastic semi-aluminum structure of the front use of light-transmissive plastic molding, the back from the thermal conductivity of good performance and with reflective surface design of aluminum alloy profiles. In the outer surface of aluminum profile stripes or fins to increase the heat dissipation area, the structure shown in Figure 3.

All plastic tubes made of plastic, including: the whole root all use the same plastic, positive and negative use of different plastics (positive use of translucent plastic, the back of the use of milky white plastic to block the back of the PCB and the lamp drive power , So that light and beautiful lamp). Transparent plastic PMMA (PMMA) and flame-retardant PC (polycarbonate) two. Full PC material drawing or diffuse transmission, making the light angle as large as shown in Figure 4 structure.

All-glass lamp made of glass, LED light source installed in the front of the aluminum plate, the back through the thermal plastic glue directly on the inner wall of the glass lamp. Glass tube coated with diffuse coating on the inner wall, the light uniform, soft, reduce glare. The structure is shown in Fig.

The three kinds of LED tube lamps

Glass tube LED fluorescent light transmission performance is better than the other two, the luminous flux higher luminous efficiency is also the highest. The color rendering index of the light source mainly depends on the spectral power distribution of the light source. The spectral transmittance of the light-transmitting material is relatively flat in the visible region, and the color rendering index is almost the same. Semi-plastic semi-aluminum LED fluorescent lamp the maximum light intensity of the largest, all-glass LED fluorescent lamp due to uniform diffusion layer, the average beam angle is the largest. The average beam angle of a single material LED fluorescent lamp is better than that of a semi-plastic semi-aluminum LED fluorescent lamp, while the semi-plastic semi-aluminum LED fluorescent lamp has the smallest luminous angle due to the limitation of the heat dissipation aluminum material. LED fluorescent light and 360 ° compared to the traditional fluorescent lamp, due to the substrate and chip light-emitting surface constraints, has always been unable to full-angle light, as shown in Figure 6. Figure (b) shows a slight deviation of the light distribution curve relative to the axis of symmetry, is a fluorescent test with a defect, does not affect the measurement of the angle of light.

LED fluorescent lighting is a semi-direct lighting, translucent material made of light cover the upper part of the light source, 60% to 90% of the light focused on the face, 10% to 40% covered light diffuse through the translucent shade and upward Shot, the light is softer. Such lamps are commonly used in general lighting of lower rooms. As the diffuse light can illuminate the flat top, so that the top of the room brightness increases, which can produce a greater sense of space. Therefore, LED fluorescent lamp in the spatial distribution, it is necessary to consider the luminous angle, but also consider the light uniformity of the work surface.

The abscissa and ordinate in Figure 7 represent the horizontal and vertical angles of the face respectively. The color lines in the figure represent different light intensities, blue represents 90% of the peak intensity, the brown represents 80%, and the red represents 10% , To 10% decline. Visible in the middle of the first line is the blue line, which is facing the LED fluorescent lamp face to receive the maximum light intensity, away from the center of the light intensity decreases. The less part of the middle part of the color line, that is, the less the gradient of light intensity, indicating the intensity of LED fluorescent light projected to the work surface is smaller with the angle slowly, the better uniformity of light.

Table 3, Table 4 is the color coordinates of the three types of fluorescent data and color parameters. Can be seen, both the average color coordinates or the center of color coordinates, three types of LED fluorescent light-emitting area in the vicinity of the standard white E. Further, the chromaticity performance of each LED fluorescent lamp at each angle was analyzed for two dimensional (Cangle, Gammaangle) chromaticity measurements.

Fig. 9 to Fig. 11 show the three-dimensional color difference distribution of the LED fluorescent lamp. Can be seen that each LED fluorescent chromaticity index has two curves, one for the Cangle is equal to 0 ° curve, representing the axial chroma performance, and the other for the Cangle is equal to 90 ° curve, representing the radial chroma performance . Three types of LED fluorescent lamp in the axial and radial chromaticity have a certain range of fluctuations. All plastic LED fluorescent lamp axial color coordinates of the smallest fluctuations, the stability of the best. For LED fluorescent lamp radial color performance, that is, Cangel is 90 ° when the lights on the point of the color coordinates.

From the measured data show that the plastic LED fluorescent lamp color coordinates in addition to individual points, the whole is relatively stable; semi-plastic semi-aluminum LED fluorescent tube and all-glass LED fluorescent fluctuations significantly. Visible color uniformity, the full performance of plastic LED fluorescent lamp the best. Three types of LED fluorescent lamp in the color saturation is not very different.

1.3 structure and material on the thermal performance

LED light source, due to heat to the light source temperature, resulting in light failure, thereby shortening the life of LED fluorescent lamp. Good structure and materials can effectively reduce the temperature of the lamp to ensure its normal use. The experiment was carried out in a 5m × 10m × 5m indoor environment (Figure 12). The installation height of the fixture was 2m, and the surface temperature of the fixture was measured every 0.5h. First of all, to discuss the semi-plastic semi-aluminum LED fluorescent lamp cooling performance, the lamp consists of two parts of the lampshade, half of the PC lampshade, is the light-emitting surface, the other half for the aluminum heat sink, LED light board is located in the middle of the tube close to the aluminum alloy Shade at. The temperature was measured on the front side and the back side of the heat radiation, respectively, and the room temperature was 25.9 ° C. The results are shown in Table 5. All plastic LED fluorescent tube for the PC, LED lamp circuit board at the top of the lamp board and lamp wall left a little gap. Test room temperature is 27.5 ℃, the test data) as shown in Table 6. All-glass LED fluorescent lamp tube material for all-glass, similar to the whole structure of plastic tubes. Test room temperature is 27.0 ℃, the test data shown in Table 7.

It can be seen that the difference between the temperature rise of the LED fluorescent lamp and the backlight surface after the same time is larger, because the LED chip is closer to the backlight surface, and the heat generated by the core is guided more by heat conduction glue or heat sink back. Fig. 15 is a temperature rise graph of the LED light-emitting surface and the backlight surface.

Can be seen, all-glass LED fluorescent light-emitting surface of the cooling performance than the other two fluorescent lamp is slightly superior, the whole plastic structure and semi-plastic semi-aluminum structure of the light-emitting surface are PC material, heat performance almost. In the back, semi-plastic semi-aluminum LED fluorescent lamp cooling the best performance, minimum temperature, and the temperature is more stable, all-glass LED fluorescent lamp temperature rise maximum, all plastic center.

2.LED bulb light

The structure of the LED bulb includes a light shell, an LED lighting unit, a heat radiator, a driving power source, a lamp body and a lamp cap.

Which LED bulb lamp shell generally use high transmittance PC, PMMA material, usually using frosted, with anti-glare, increasing the effect of lighting area. The LED light-emitting unit comprises an LED chip and a substrate, and the substrate material is usually an aluminum material or a metal core PCB board. Heat a body of aluminum alloy, plastic materials, such as thermal conductivity of plastic materials, thermal radiation through the heat and air convection cooling. By testing four identical power (3W) LED bulb, compare the arrangement of different chips and different thermal materials on the LED light bulb light and heat performance.

2.1 chip arrangement on the impact of light measurement

In this paper, the market representative of the three brands of 3 LED bulb (Philips, the state, Caesar). Will these three kinds of chip arrangement way is called module 1, module 2, module 3 respectively. One module on behalf of the Philips LED Bulb lamp chip arrangement, similar to the two closed arc structure, and placed in the middle of a substrate chip; module 2 represents the state of the LED bulb chip arrangement , Which through the three and the radiator was placed in a certain angle up the substrate, a number of LED chips are encapsulated on it; module three on behalf of Caesar light LED bulb lamp chip arrangement, which is uniform circular distribution. Optical measurement parameters are shown in Table 8. Can be seen, the overall performance of Philips LED Bulb than the state, Caesar light good.

Module 2 LED bulb lamp is used in full-angle packaging mode, the largest angle of light, the module one and module three block due to the substrate, the light angle decreases. The light distribution curves of the three types of bulbs are shown in Fig. 18 and Fig.

Module 2 in the horizontal direction of the light intensity of the largest, facing the face of the light intensity is relatively small. Module 1 and Module 3 of the light intensity distribution is relatively similar, are facing the face of the light intensity of the largest, slowly around the smaller, one module of the light intensity is slightly larger than the module three. From the three types of light bulb lamp intensity curve can be seen that the module with a module of the uniformity of almost three, light intensity is slowly decreasing from the middle to the surrounding. Module II of the light is chaotic, indicating that the expansion of the light angle at the same time not well take into account the uniformity.

effect of structural materials on the thermal performance of led Fluorescent tube lamp and led bulb

2.2 chip layout on the color coordinates of the impact

The color coordinates and color metrics are shown in Table 9 and Table 10. The three-dimensional chromatic aberration diagram (Fig. 20 ~ Fig. 22) was obtained by testing GO-R5000 full-space rapid-distribution photometer for three kinds of bulb lamps. Through the three-dimensional chromatic aberration diagram, u ‘and v’ parameters Overall symmetrical, this is different from the LED fluorescent lamp, LED bulb because the luminous body structure is rotationally symmetrical.

From the stability of the color coordinates, the module is stable in the whole Gamma angle, especially v ‘coordinate, almost no change, the edge of the mutation is because the detector turned to the top of the bulb; The bulb lamp is also stable throughout the Gamma angle, but the curve is not a rounded module, there are some small fluctuations, v ‘coordinates in the vicinity of the central area of ​​stability than the two sides; module three color coordinates stability than the module One and module two slightly worse, especially the v ‘coordinates, 108 ° ~ 180 ° stability is very bad. The color coordinates of the module one of the best stability, the second module.

2.3 Materials on the thermal performance

LED bulb heat dissipation is mainly through the radiator, the radiator is mainly hollow cylindrical structure or cone ring structure, compared with LED fluorescent lamp, the heat dissipation area is small, so the radiator material determines the bulb heat dissipation . The heat dissipation performance of three kinds of radiator materials was tested by experiment. Three kinds of radiator materials are thermal plastic, aluminum alloy and ceramic. The experimental site is about 5m × 10m × 5m indoor environment, lighting installation height of 2m, measured once every 0.5h lamp surface temperature, the use of temperature to characterize. Test environment temperature is 26.9 ℃, the test site shown in Figure 23.

Aluminum radiator LED bulb thermal conductivity, small thermal resistance. But the cost is high. Aluminum itself is a conductor, there is leakage safety hazards. The test data are shown in Table 11. Thermal plastic is a high thermal conductivity fillers, additives and other additives in the engineering plastic substrate. General plastic thermal conductivity is only 0.14 ~ 0.34W / (m · K), thermal plastic up to 1 ~ 20W / (m · K), is the traditional plastic 50 to 100 times. Lighter than aluminum, and insulation performance, and improve security. The test data are shown in Table 12.

Ceramic thermal conductivity is higher, in the natural air convection, can be used as LED bulb heat sink material. Ceramic sintering technology is mature, can be enamel into different colors, and electrical insulation. But the ceramic cooling fins can not be too thin (thickness of not less than 1.5mm), easy to produce cracks in the high stress, non-glaze surface pollution. The test data in Table 13 (unit: ℃). Three types of bulb lamp shell and radiator temperature rise diagram shown in Figure 24.

From Figure 24, although the polyline a little beating, lamp shell and the temperature rise of the radiator is the same trend, the best thermal performance of plastic thermal conductivity, followed by aluminum, ceramic worst. Although the thermal conductivity of plastic thermal conductivity is less than aluminum, but its surface emissivity is higher than aluminum, thermal plastic surface emissivity can reach 0.93, while the aluminum is generally 0.2 to 0.3, thereby reducing the lamp temperature. Ceramic radiator due to the relationship between the thickness of the thermal conductivity of aluminum and thermal conductivity of plastic.

3. Summary

In this paper, the effect of color temperature on the luminescent properties of LED fluorescent lamps, especially the color rendering index and luminous efficiency, is studied. With the increase of LED color temperature, the luminescent efficiency of LED lamps decreases slowly, and the color rendering index increases. Then, the light and heat properties of the semi-plastic semi-aluminum LED fluorescent lamp, full plastic LED fluorescent lamp and all-glass LED fluorescent tube are compared. Under the same power condition, the luminous flux of all-glass LED fluorescent lamp is the largest, But also three types of LED fluorescent lamps in the highest, followed by the whole plastic structure. Due to structural differences, all-glass structure and the whole plastic structure of the LED fluorescent light angle is much larger than the semi-plastic semi-aluminum structure fluorescent lamp, which the whole glass structure of the fluorescent light angle of the maximum. As the semi-plastic semi-aluminum structure of the light angle of the smallest, the light energy constraints in a smaller range of light, so the peak light intensity is the largest of the three types of fluorescent lamps, all-glass structure.

In the luminous uniformity parameters, the semi-plastic semi-aluminum LED fluorescent tube structure the most uniform, followed by the whole plastic structure. For the stability of the color coordinates, all-plastic fluorescent lamp is the most stable. In the cooling performance, the semi-plastic semi-aluminum LED fluorescent lamp cooling the best performance, cooling is also the most stable, followed by the whole plastic structure.

In general, the test of the three types of LED fluorescent lamps have advantages and disadvantages in the light measurement parameters, all-glass LED fluorescent performance best, but the light uniformity and color coordinate stability to be improved, the other cooling performance also The development of space; color measurement, the plastic LED fluorescent color coordinates of the most stable, and other light measurement parameters and thermal performance of the whole plastic LED fluorescent performance is mediocre, in a compromise position; in the cooling performance and light uniformity, Aluminum LED fluorescent lamp the best performance, but its luminous flux and luminous efficiency there is room for development, while the smaller the angle of light is its disadvantage. Through the experimental test analysis of a variety of LED bulb light and heat performance, from the light measurement and color measurement point of view, large companies produce LED bulb performance to be more superior. Thermal performance, the thermal conductivity of plastic LED bulb as the radiator can play a better cooling effect.

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