LED fluorescent lamps and LED bulbs have been widely used as typical light sources for LED illumination. Structures and materials can have an impact on their performance. In the case of fluorescent lamps, the material of the tube not only affects the luminosity parameters of the luminaire, but also affects reliability. The chip arrangement on the bulb substrate also has a certain effect on the light color parameters. The electro-optical conversion efficiency of white LED light source is generally about 30%, most of the electricity
The energy is converted into heat, and the heat is transferred to the heat sink member through the substrate, and the air convection through the surface of the heat sink member is dissipated. The heat dissipation efficiency affects the light output efficiency and service life of fluorescent lamps or bulbs. In this paper, the effects of structure and materials on the light, color and thermal properties of LED fluorescent lamps and LED bulbs are compared and analyzed through experimental research.Fluorescent lamp
1.1 Effect of color temperature on optical performance
Song Guohua and others studied the relationship between LED color temperature, luminous efficiency, and color rendering index. The experimental results are shown in Figure 1. It can be seen that when the color temperature of white LED is greater than 4000K, as the color temperature increases, the luminous efficiency shows a slow downward trend, while the color rendering index shows an upward trend. Experiments were carried out on three different color temperature LED fluorescent lamps (NVC3000K, NVC4000K, NVC6000K) of the same model. The results are shown in Table 1, which verified this trend.
The color rendering of a light source depends on its spectral power distribution, and the source of the continuous spectrum has better color rendering. The increase in color rendering index is accompanied by a decrease in luminous efficiency, and it also indicates that the color temperature indirectly affects the luminous efficiency of the LED fluorescent lamp.
1.2 The effect of structure on optical properties
The structure of the LED fluorescent lamp is shown in Figure 2.
LED fluorescent lamp housing lamp is mainly used to protect, locate, connect components, heat dissipation, optimize lighting effects. The lamp includes: all-plastic, all-glass, semi-plastic semi-aluminum structure. The T8 LED fluorescent lamp was tested on the same power T8 LED fluorescent lamp to discuss the influence of the structure on the optical performance of the LED fluorescent lamp. The semi-plastic semi-aluminum structure is formed by a transparent plastic front, and the back side is made of an aluminum alloy profile with good thermal conductivity and a reflective surface design. Shape the stripe or fin on the outer surface of the aluminum profile to add heat dissipation area. The structure is shown in Figure 3.
All plastic tube tubes are made of plastic, including: the whole plastic is made of the same plastic, different plastics are used on the front and back sides (translucent plastic is used on the front side, and milky white plastic is used on the back side to block the back of the PCB and the driving power in the tube) To make the tube light and beautiful). Light-transmissive plastics are available in PMMA (Plexiglas) and Flame Retardant PC (Polycarbonate). The whole PC material is drawn or diffused to make the light exit angle as large as possible. The structure is shown in Figure 4.
The all-glass tube is made of glass, and the LED light source is mounted on the front side of the aluminum substrate , and the back side is directly adhered to the inner wall of the glass tube through the thermal conductive adhesive. The inner wall of the glass tube is coated with a diffuse scattering coating to make the light uniform and soft, reducing glare. The structure is shown in Figure 5.
The LED fluorescent lamps (same power, different structures) of the three lamp structures were tested. The results are shown in Table 2.
The light transmittance of the glass tube LED fluorescent lamp is better than the other two, the luminous flux is higher, and the luminous efficiency is also the highest. The color rendering index of the luminaire mainly depends on the spectral power distribution of the light source. Since the spectral transmittance of the light-transmitting material is relatively flat in the visible region, the color rendering index of the three is almost the same. The semi-plastic semi-aluminum structure LED fluorescent lamp has the highest peak intensity, and the all-glass LED fluorescent lamp has the largest average beam angle due to the uniform diffusion layer. 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 illumination angle due to the limitation of the heat-dissipating aluminum material. Compared with traditional fluorescent lamps with 360° illumination, LED fluorescent lamps cannot always emit light at all angles due to the limitation of the substrate and the light-emitting surface of the chip, as shown in Fig. 6. The light distribution curve shown in Figure (b) is slightly offset from the axis of symmetry. It is a measurement of the fluorescent lamp used in the experiment and does not affect the measurement of the illumination angle.
The illumination of LED fluorescent lamps belongs to semi-direct illumination. The lampshade made of translucent material covers the upper part of the light source. 60%~90% of the light is concentrated on the working surface, and 10%~40% of the light is diffused through the translucent lampshade. Shot, the light is softer. This type of luminaire is often used for general lighting in lower rooms. Since the diffused light can illuminate the flat top, the brightness of the top of the room is increased, so that a large sense of space can be produced. Therefore, in the spatial distribution of the LED fluorescent lamp, both the illumination angle and the light uniformity on the working surface must be considered.
The abscissa and ordinate in Figure 7 represent the horizontal and vertical angles of the working surface, respectively. The colored lines in the figure represent different light intensities, blue represents 90% of the peak intensity, brown represents 80%, and red represents 10%. , decremented by 10%. It can be seen that the first line of the middle area is a blue line, that is, the light intensity received from the working surface facing the LED fluorescent lamp is the largest, and the light intensity away from the center is reduced. The less the color line in the middle part, the less the gradient of the light intensity changes, indicating that the light intensity of the LED fluorescent lamp projected onto the working surface is gradually smaller with the angle, that is, the uniformity of the light emission is better.
Table 3 and Table 4 are the color coordinates and color parameter data of the three types of fluorescent lamps. It can be seen that the illumination color area of ​​the three types of LED fluorescent lamps is in the vicinity of the standard white light E, regardless of the average color coordinate or the central color coordinate. Further, the chromaticity performance of each LED fluorescent lamp at each angle is analyzed for two dimensional (Cangle, Gammaangle) colorimetric measurements.
9 to 11 are three-dimensional color difference distribution diagrams of LED fluorescent lamps. It can be seen that the chromaticity index of each type of LED fluorescent lamp has two curves, one of which is a curve with Cangle equal to 0°, representing axial chromaticity performance, and the other is a curve with Cangle equal to 90°, representing radial chromaticity performance. . The three types of LED fluorescent lamps have a range of fluctuations in the axial and radial chromaticities. The all-plastic structure LED fluorescent lamp has the smallest axial color coordinate fluctuation and the best stability. For the radial color performance of LED fluorescent lamps, that is, the color coordinates of each point on the fixture when Cangel is 90°.
From the measured data, it can be seen that the color coordinates of the all-plastic LED fluorescent lamp are generally stable except for individual points; the fluctuations of the semi-plastic semi-aluminum structure LED fluorescent lamp and the all-glass LED fluorescent lamp are obvious. It can be seen that for the uniformity of color, the all-plastic LED fluorescent lamp performs best. The three types of LED fluorescent lamps have little difference in color saturation.
1.3 The influence of structure and material on heat dissipation performance
When the LED light source emits light, the temperature of the light source rises due to heat, resulting in light decay, thereby shortening the service life of the LED fluorescent lamp. Good structure and materials can effectively reduce the temperature of the lamp and ensure its normal use. The experiment was carried out in a 5m×10m×5m indoor environment (Fig. 12). The installation height of the lamp was 2m, and the surface temperature of the lamp was measured every 0.5h. Firstly, the heat dissipation performance of the semi-plastic semi-aluminum LED fluorescent lamp is discussed. The lamp tube is composed of two parts of the lampshade, half of which is the PC lamp cover, facing the light-emitting surface, and the other half is the aluminum alloy heat-dissipating surface. The LED lamp circuit board is located in the middle of the lamp tube slightly close to the aluminum alloy. At the lampshade. The temperature was tested on the front side of the light and the back side of the heat sink, and the room temperature was 25.9 ° C. The results are shown in Table 5. The all-plastic LED fluorescent tube is a full PC, and the LED light circuit board is located at the top of the lamp tube, leaving a slight gap between the lamp board and the wall of the lamp tube. The room temperature was 27.5 ° C during the test, and the test data thereof is shown in Table 6. The all-glass LED fluorescent tube material is all-glass, and the structure is similar to that of an all-plastic tube. The room temperature was 27.0 ° C during the test, and the test data is shown in Table 7.
It can be seen that the difference in temperature rise between the light-emitting surface and the backlight surface of the LED fluorescent lamp is relatively large, because the LED chip is closer to the backlight surface, and the heat generated by the core is more directed through the thermal conductive adhesive or the heat dissipation plate. back. Figure 15 is a graph showing the temperature rise of the light-emitting surface and the backlight surface of the LED fluorescent lamp.
It can be seen that the heat dissipation performance of the light-emitting surface of the all-glass structure LED fluorescent lamp is slightly superior to that of the other two fluorescent lamps, and the luminous surfaces of the all-plastic structure and the semi-plastic semi-aluminum structure are all PC materials, and the heat dissipation performance is similar. On the back side, the semi-plastic semi-aluminum structure LED fluorescent lamp has the best heat dissipation performance, the lowest temperature rise, and the temperature is relatively stable. The all-glass structure LED fluorescent lamp has the highest temperature rise and the whole plastic is centered.
2.LED bulb
The structure of the LED bulb includes a lamp housing, an LED lighting unit, a heat sink, a driving power source, a lamp body and a lamp cap, and the structure thereof is shown in FIG.
The lamp housing of the LED bulb is generally made of PC and PMMA with high light transmittance, and is usually treated with a matte finish, which has the effect of preventing glare and increasing the illumination area. The LED lighting unit includes an LED chip and a substrate, and the substrate material is usually an aluminum material or a metal core PCB board. The heat sink has an aluminum alloy material, a heat conductive plastic box ceramic material, etc., and is radiated by heat radiation of the heat sink and air convection. By testing 4 ç› the same power (3W) LED bulb, compare the different chip layout and the effect of different heat dissipation materials on the photothermal performance of the LED bulb.
2.1 The impact of chip layout on light metrics
This article selects 3 LED bulbs (Philips, Benbon, Kasaro lamps) with three brands on the market. These three types of chip layout are called module one, module two, and module three. Module 1 represents the chip arrangement of Philips LED bulbs, which is approximately two non-closed arc structures, and a chip is placed in the center of the substrate; module 2 represents the chip arrangement of the state LED bulbs. The plurality of LED chips are packaged thereon by three substrates placed at an angle with the heat sink, and the module 3 represents a chip arrangement of the Caesar lamp LED bulbs, which is a uniform circular distribution. The light metric parameters are shown in Table 8. It can be seen that the overall performance of the Philips LED bulb is better than that of the state and the Caisal.
The module 2 LED bulb adopts a full-angle encapsulation mode, and the exit angle is the largest, and the module 1 and the module 3 are reduced due to the shielding of the substrate. The light distribution curves of the three types of bulbs are shown in Figs. 18 and 19.
Module 2 has the highest light intensity in the horizontal direction of the luminaire, and the light intensity facing the working surface is relatively small. The light intensity distribution of module one and module three are relatively similar, and the light intensity directly facing the working surface is the largest, and gradually decreases toward the periphery, wherein the intensity of the module one is slightly larger than that of the module three. It can be seen from the equal light intensity curves of the three types of bulbs that the uniformity of the module one is similar to that of the module three, and the light intensity is gradually decreasing from the middle to the periphery. The light output of Module 2 is rather confusing, indicating that it does not have a good balance of uniformity while expanding the exit angle.
2.2 The effect of chip layout on color coordinates
The color coordinates and color metrics are shown in Tables 9 and 10. The GO-R5000 full-space fast-distribution photometer was used to test the three types of bulbs to obtain a three-dimensional chromatic aberration diagram (Fig. 20 to Fig. 22). Through the three-dimensional chromatic aberration diagram, the u' parameter and v' parameter of each bulb were known. It is generally symmetrical, which is different from LED fluorescent lamps because the illuminant structure of the LED bulb is rotationally symmetrical.
From the stability of the color coordinates, the module-ball lamp is stable throughout the Gamma angle, especially the v' coordinate, with almost no change. The edge is abrupt because the detector is turned to the top of the bulb; Module 2 The bulb is also stable over the entire Gamma angle, but the curve has no roundness of the module, there are some small fluctuations, the stability of the v' coordinate is closer to the central area than the two sides; the color coordinate stability of the module three is better than the module. One is slightly worse than the second, especially the v' coordinate, and the stability at 108° to 180° is very bad. The color coordinate stability of module one is the best, and the module is second.
2.3 Influence of materials on heat dissipation performance
The heat dissipation of the LED bulb is mainly through the radiator. The radiator is mainly a hollow ring column structure or a cone ring structure. Compared with the LED fluorescent lamp, the heat dissipation area is small, so the material of the radiator determines the heat dissipation performance of the bulb. . The thermal performance of the bulb light of the three heat sink materials was tested experimentally. The three heat sink materials are heat conductive plastic, aluminum alloy and ceramic. The experimental site is an environment of about 5m×10m×5m indoors. The installation height of the lamps is 2m. The surface temperature of the lamps is measured every 0.5h and is characterized by temperature rise. The ambient temperature during the test was 26.9 ° C, and the test site is shown in Figure 23.
The aluminum alloy radiator LED bulb has a large thermal conductivity and a small thermal resistance. But the cost is high. The aluminum itself is a conductor and there is a safety hazard of leakage. The test data is shown in Table 11. The heat conductive plastic is a high thermal conductive filler, an auxiliary agent or the like added to an engineering plastic substrate. The thermal conductivity of general plastics is only about 0.14 ~ 0.34W / (m · K), thermal plastics can reach 1 ~ 20W / (m · K), 50 ~ 100 times that of traditional plastics. It is lighter than aluminum and has good insulation properties for improved safety. The test data is shown in Table 12.
Ceramics have a high thermal conductivity and can be used as a heat sink material for LED bulbs under natural convection of air. The ceramic sintering technology is mature, can be glazed into different colors, and is electrically insulated. However, the fins of ceramics should not be too thin (thickness not less than 1.5 mm), cracks are likely to occur under medium-high stress, and unglazed surfaces are easily contaminated. The test data is shown in Table 13 (unit: °C). The temperature rise diagram of the three types of bulb lamp housings and radiators is shown in Figure 24.
From Fig. 24, although the fold line is a little beat, the temperature rise trend of the lamp housing and the heat sink is the same, the heat dissipation performance of the heat conductive plastic is the best, the aluminum alloy is the second, and the ceramic is the worst. Although the thermal conductivity of the heat-conductive plastic is not as good as that of the aluminum material, the surface radiance is higher than that of the aluminum material. The surface radiance of the heat-conductive plastic can reach 0.93, and the aluminum material is generally 0.2-0.3, thereby lowering the temperature of the lamp. Due to the thickness of ceramic heat sink, thermal conductivity is inferior to aluminum and thermal plastic.
3. Summary
This paper explores the influence of color temperature on the luminescence performance of LED fluorescent lamps, especially the color rendering index and light efficiency. As the color temperature of LED increases, its luminous efficiency shows a slow decline, while its color rendering index shows an upward trend. Then through experiment, compare the photothermal performance of semi-plastic semi-aluminum structure LED fluorescent lamp, all-plastic structure LED fluorescent lamp and all-glass structure LED fluorescent lamp: under the same power condition, the all-glass structure LED fluorescent lamp has the largest luminous flux, so its light effect It is also the highest of the three types of LED fluorescent lamps, followed by the all-plastic structure. Due to the structural difference, the all-glass structure and the all-plastic LED fluorescent lamp have a much larger light-emitting angle than the semi-plastic semi-aluminum fluorescent lamp, and the all-glass fluorescent lamp has the largest light-emitting angle. Since the semi-plastic semi-aluminum fluorescent lamp has the smallest exit angle, it limits the light energy to a smaller light-emitting range, so its peak light intensity is the largest among the three types of fluorescent lamps, and the all-glass structure is second.
In the illuminance uniformity parameter, the semi-plastic semi-aluminum structure LED fluorescent lamp is the most uniform, and the all-plastic structure is second. For the stability of color coordinates, all-plastic fluorescent lamps are the most stable. In terms of heat dissipation performance, the semi-plastic semi-aluminum structure LED fluorescent lamp has the best heat dissipation performance, the heat dissipation is also the most stable, and the all-plastic structure is second.
In general, the three types of LED fluorescent lamps tested have their own advantages and disadvantages. In terms of light measurement parameters, all-glass LED fluorescent lamps perform best, but their uniformity of light output and stability of color coordinates still need to be improved, and heat dissipation performance is also Development space; in color metrics, the color coordinates of the all-plastic LED daylight lamp are the most stable, and all the light metric parameters and heat dissipation performance of the all-plastic LED fluorescent lamp are flat and in a compromised position; in the heat dissipation performance and the uniformity of light output, the semi-plastic half The aluminum-structured LED fluorescent lamp performs best, but its luminous flux and luminous efficiency still have room for development, and the smaller the light-emitting angle is also its disadvantage. Through the experimental test analysis and comparison of the photothermal performance of various LED bulbs, from the perspective of light measurement and color measurement, the performance of LED bulbs produced by large companies is more superior. In terms of heat dissipation performance, the heat conductive plastic acts as a heat sink for the LED bulb lamp to provide better heat dissipation.
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