With the improvement of LED chip light efficiency, continuous improvement of packaging technology, and the development of LED lamp heat dissipation technology, LED light source has expanded rapidly in the field of lighting, and the LED panel lamp industry has prospered.
LED panel light has many advantages such as uniform illumination, low glare, simple installation, etc. The market has good development prospects and leads the new trend of modern fashion interior lighting. However, the quality of LED panel lights on the market is currently uneven. Some manufacturers disregard the quality of products, suppressing prices and vicious competition, which seriously affects the healthy development of the industry.
Since the LED panel light has not yet issued national standards, in 2014, China Electronics Industry Standardization Technology Association and Huaju Industry Common Standard Promotion Foundation jointly announced the cross-strait common standard GT004-2012 "indoor general lighting LED panel lamps", LED panel lights Safety and performance regulations have been made to standardize the quality requirements of LED panel lights. As a reference for the production of flat panel lamps, market management can also be implemented. Refer to the common requirements of the two sides of the strait, the following how to control the quality of LED panel lights.
Structural features
The LED panel light structure is unique compared with other lamps. It is mainly composed of a light source, a light guide plate, a diffusion plate, a reflective paper, a driving power source, etc., and has more LED backlights than other lamps, such as a light guide plate, a diffusion plate, and a reflective paper. The structure of the product.
(1) LED light source
LED panel light manufacturers basically use SMD patch series in the use of LED light sources, such as 3528, 3014 and so on. The market faced by LED panel light manufacturers is dynamic, and manufacturers will select the light source that meets the design requirements according to the actual needs of customers. The choice of LED light source is critical to product performance improvement and is one of the important factors to improve the quality of LED panel light.
(2) Light guide plate
The function of the light guide plate is to convert the light emitted by the LED point light source into a surface light source through optical technology, and refract the side LED light through the dot to make the light uniformly output from the front side. At present, the printed light guide plate is mainly used, and the quality of the light guide plate directly affects the brightness and uniformity of the product, and requires good light transmission performance.
The light guide plate is the key point for the quality control of the LED panel light. The design of the dot is not good, the overall light effect is poor, and the light is not uniform. There are also bright lights on both sides of the middle, bright bands at the light, visible dark areas, and different The angle brightness is inconsistent. To improve the light effect of the light guide plate mainly depends on the design of the mesh point, followed by the quality of the plate, and it is preferable to select the qualified plate with high light transmittance.
(3) diffuser
The main function of the diffuser is to evenly direct the light from the light guide plate to make the light distribution more uniform. When the light hits the diffusion point, the reflected light will diffuse at various angles, and then be emitted from the front surface of the light guide plate, and the light guide plate is uniformly illuminated by various dense and different diffusion points, thereby improving the brightness of the light guide plate. Can also play the role of fuzzy outlets.
The diffuser board generally uses Acrylic 2.0 sheet or PC material, which is almost the PS material. Acrylic has lower cost and light transmittance than PC, and its anti-aging performance is weak; PC is slightly expensive, but has strong anti-aging properties. The diffuser plate cannot see the dots after being mounted, and the light transmittance is about 90%. The acrylic transmittance is 92%, the PC is about 90%, and the PS is about 88%. Manufacturers can choose the diffuser material according to their needs. At present, most manufacturers use acrylic materials.
(4) Reflective paper
The function of the reflective paper is to totally reflect the light under the light guide plate, so that the light emitted by the LED can be fully utilized. As far as possible, the reflection rate is close to 100% reflective paper, so that the light utilization is maximized, and the output brightness of the LED panel lamp is improved. For RW250.
(5) Rear cover
The main function is to seal the LED panel light, generally using aluminum plate, and also can play a heat dissipation role.
(6) Drive power
At present, there are two kinds of LED driving power sources . One is to use constant current power supply. This mode has high efficiency, the PF value is up to 0.95, and the cost performance is high. The second is to use constant voltage with constant current power supply. The performance is stable, but the efficiency is low and the cost is high. This kind of power supply is mainly for export, and the other party has certification requirements. In fact, it is safe to use a constant current power supply in the home because it is difficult for the user to access the power supply, and the lamp body itself uses a safe low voltage.
Performance improvement
Performance is an important indicator for evaluating the performance of LED panel lights. Luminous efficacy is the ratio of the luminous flux emitted by a light source to the electrical power it consumes, in lm/W. Luminaire efficacy is the ratio of the initial total luminous flux emitted by a luminaire to the power it consumes, in lm/W, under the claimed conditions of use of the luminaire.
"Light effect" is used to evaluate LED light source. "Lighting performance" is used to evaluate LED lamps. LED light source efficacy and LED lamp efficiency all indicate the efficiency of converting electrical energy into light energy. It is an indicator to describe the energy-saving characteristics of lighting products, but its connotation It is different. According to the GT004-2012 "Indoor Indoor Lighting LED Panel Lamps" standard, the measurement should be carried out in an airless convection environment with a relative humidity of not more than 65% and a temperature of 25 °C ± 1 °C, and the LED panel lamps should be in a stable working state. .
The luminous flux of the light source in the light source of the LED light source refers to the luminous flux emitted by the bare light source (the state not yet installed in the luminaire). The molecular luminous flux in the performance of an LED luminaire refers to the luminous flux emitted by the luminaire after the light source is installed in the luminaire and the power of the required LED control device or LED control device is used. The LED light source consumes less electrical power than the LED luminaire consumes.
LED light source efficacy is much greater than the efficacy of the luminaire. One is because the color temperature rises and the light output decreases after the LED enters the lamp; the second is because of the system loss after the light source enters the lamp, after using the LED control device or the power supply; the third is the loss of light after passing through the optical system of the lamp, Factors will cause the light efficiency of the luminaire to decrease. GT004-2012 "LED flat panel lamps for indoor general lighting" standard specifies the performance level of lamps with different color temperatures (below).
When testing LED panel lights, it is found that the following two points must be improved to improve performance: First, to select high-efficiency, high-brightness LEDs, which can improve performance and reduce costs, and more importantly, improve the quality of LED panel lights. The second is to make full use of the light emitted by the LED. If you only pay attention to the brightness of the LED, but fail to design and improve the optical path, effectively improve the utilization of light, and the effect on improving the performance of the LED panel light is not great.
From the LED light source to the light guide plate and reflector, until the final LED panel light shows the output process, the light utilization rate will be reduced by about 30% from the brightness index, and the LED panel light will not be used from the light guide plate to the final utilization. 70%. In order to improve the light utilization rate, it is necessary to select materials such as light guide plates and reflective papers of good quality, which not only meet the technical specifications of the design of LED flat lamps, but also cooperate with each other in terms of specifications. Because the direct-type module is thicker and does not conform to the trend of lightness and beauty, it is currently dominated by sidelights.
The function of the light guide plate is to guide the scattering direction of the light, which is used to increase the brightness of the panel and ensure the uniformity of the brightness of the panel. The light guide plate applied now is getting thinner and thinner, and its quality has a great influence on the quality of the LED panel light. The light transmittance and optical uniformity index of the light guide plate are the key to the improvement of the performance of the edge light type LED panel light.
The light guide plate is formed by injection molding to make propylene into a smooth surface plate, or by using an off-the-shelf acrylic plate, the light transmittance is over 90%; then, the material having high reflection and not absorbing light is used in the light guide plate. The bottom surface is printed with a diffusion dot by means of a screen printing, and the reflective paper totally reflects the light overflowing the bottom surface back into the light guide plate for improving the light use efficiency and the front brightness. After laboratory tests, the results show that the LED panel light produced by LED professional manufacturers can reach 110 lm/W at a color temperature of 5500K, but there are not many manufacturers that can achieve the performance level.
Good uniformity
Another important indicator of LED panel light is the uniformity of its illumination. The common standard GT004-2012 "LED flat panel lamps for indoor general illumination" on both sides of the strait proposes the requirement of brightness uniformity, which means the minimum brightness of the illuminating surface of the luminaire. The ratio of the arithmetic mean of the brightness.
As an LED panel light, unevenness of illumination will result in uniform brightness of the panel display, causing discomfort to the human eye. According to the GT004-2012 standard requirements, the brightness uniformity of LED flat panel lamps should be not less than 0.8. The test method is mainly based on the size of the screen, select the appropriate test points, and measure the brightness value of each point.
The side length L of the square, the long side L of the rectangle, and the LED panel luminaire with a diameter D of not more than 20 cm are arranged as shown in the following figure (a); the LED panel luminaires larger than 20 cm are arranged as shown in the figure (b). The diameter of the test spot on the light-emitting surface of the LED panel lamp is 2cm to 3cm, and the brightness value of each point is subtracted from the average brightness to take the maximum value, and then the maximum value is divided by the average brightness to obtain the brightness uniformity. It is generally believed that a uniform performance of more than 80% has little effect on the perception of the human eye.
The brightness uniformity test of flat panel lamps is the first requirement in the standard for the surface brightness of indoor lamps. It embodies the characteristic parameters of flat luminaires and is one of the important features of this type of luminaire. In indoor lighting, the surface lighting fixtures create a soft and simple lighting effect that cannot be replaced by other bracket lamps or grille lamps.
In indoor lighting, fluorescent lamps with diffusing plates also have a surface-emitting effect, which has been used for many years, but does not reach the brightness uniformity level of LED flat lamps. The reason is that the fluorescent tube is an omnidirectional light source, and the optical system can no longer be adjusted to achieve better brightness uniformity, and the lamp performance is 40 lm/W. The light source of the LED lamp is a half-space light. In the lamp, the light utilization rate is high, and the lamp performance can reach 80 lm/W or more, and the brightness uniformity can reach a high level.
The LED light panel is arranged on the side of the light guide plate, and the visual effect of the lamp is better. At present, most domestic manufacturers still use a printed light guide plate as a light guide component, and use various kinds of dense and different diffusion points to make the light guide plate uniformly emit light to obtain good uniformity of illumination.
From the test results, the brightness uniformity of the small-sized LED panel light is easy to meet the requirements, and even if the uniformity is slightly deviated, the human eye is not easy to feel it. Large-area LED panel lights sometimes have unevenness in brightness due to quality problems of the light guide plate, and process light causes the above-mentioned bright light band at the light entrance, or visible partial dark area phenomenon. Therefore, the selection of the main raw materials such as light guide plate, diffuser plate, and reflective paper should be evaluated for quality, and the raw materials should be strictly controlled. The manufacturer should be equipped with the necessary optical brightness meter and transmittance test equipment.
Color difference
From the perspective of the visual sensitivity of the human eye, people are sensitive to the color of yellow and green, which means that the two colors are slightly fluctuating and can be felt by the human eye. LED flat panel lamps produced by the same manufacturer, there should be no obvious color difference between different batches of products, otherwise it is difficult for users to re-purchase the same color products after the product fails.
The standard stipulates that the light color between samples of 3 LED flat panel lamps should be consistent. The average color coordinate value of three samples should not exceed 0.004 for the average color coordinate value CIE 1976 (u'v'). At the end of the luminous flux maintenance rate test, the deviation of the chromaticity of the LED panel luminaire from the initial value should be within 0.007 of the CIE 1976 (u'v') diagram.
In LED panel light fixtures, the commonly used colors are red, green, blue, and yellow. The unit for measuring color is nm (nano). For people who are sensitive to color, as long as the color is slightly fluctuating, it can be felt. To control the color difference, you must control the raw materials. In order to avoid the difference caused by the difference in color wavelength, the lighting production company should control the LED light source.
For example, the green wavelength is 525-530 nm, separated by 5 nm, and yellow is 580-585 nm, separated by 5 nm. The red color can be 620-628nm, separated by 8nm, and the green wavelength can be felt by more than 5nm. The red color is not too obvious even within 8nm. However, from reducing the chromatic aberration and avoiding some uncertain factors caused by long-term use, such as color drift, it is better to control the wavelength of the same color within 2 nm. Therefore, the control of color indicators is often important because different people have different color discrimination capabilities.
For white light, it is usually marked with color temperature. Warm white is generally 3000-3500K, white is 3500-5000K, and cool white is 5000K-6500K. Generally, the color temperature of LEDs of packaging manufacturers is 500K apart, and there are 1000K apart. The error requirements for color temperature inside the packaging factory are generally plus or minus 200K. Therefore, the color light-stable LED light source should be selected, and the production process should be strictly controlled.
When detecting the color difference of the LED panel light, it was found that three different flat panel light samples were selected for testing. The color difference of different manufacturers' products was different, and there will be a certain gap. Some LED panel light products have color difference exceeding the standard requirements. The reason is that the manufacturer failed to carry out serious and effective screening when selecting the LED light source. The optical performance index of each LED is not consistent, resulting in different illuminating colors of different flat lamps, and the visual perception is poor when installing in a large area. Uncomfortable feeling.
To improve this common problem, first, we must do a good job of supplier evaluation, choose a relatively fixed manufacturer; second, we must propose product consistency requirements to LED suppliers to ensure continuity of supply and various performance indicators are relatively consistent and stable; Third, the company itself should also strengthen the LED purchase inspection, eliminate the LEDs whose color difference exceeds the requirements, and ensure that the uniformity of the produced LED panel lamps meets the requirements.
Problem
At present, the performance of LED devices is constantly improving, and its application range is also expanding. The dimming products of LED lamps are also constantly innovating, and the application fields are expanding. The continuous improvement of the high-brightness white LED light effect has made the demand for the side-mounted LED panel light, which has also promoted the research and development of the new LED panel light, and the new side-mounted LED panel light has emerged continuously.
However, LED panel lights also have some problems.
First, the lamp efficiency can, for side LED panel light, improve the problem of low efficacy remains a pressing problem. On the one hand, in order to achieve high brightness, it is necessary to increase the number of chips and increase the power, but the energy saving effect is not good, especially for large-sized flat lamps; on the other hand, the power increases, and the operating temperature of the LED modules in the lighting fixtures also increases. Affects light decay and longevity, so how to choose a high-efficiency LED light source needs to be considered comprehensively. At present, the commercial LED luminous efficiency has exceeded 130 lm/W.
The second is the inconsistency of light decay . Due to the large number of LEDs used in LED panel lights, the inconsistency of light decay between individuals will reduce the brightness on the one hand, and may also increase the probability of unevenness of LED panel lamps on the other hand. It is the use of RGB color LED panel lights, the LED light of different colors is different, and the possibility of unevenness is greater. Let the LED work below the rated power and sacrifice a certain efficiency. It is a better solution to reduce the light decay as much as possible.
The third is the discreteness of the parameters of the LED device . Based on the requirements of the brightness and color rendering of the LED panel lamp, when the LED panel lamp is working, the current of each LED device should be consistent under the constant voltage source condition. When the constant current source is working, the voltage should be Consistent, and the brightness and wavelength of each LED should be as consistent as possible. Therefore, the LEDs used in the same LED panel light should be screened, especially for the luminous efficiency, luminous flux, dominant wavelength, color temperature and pressure drop, etc., within a certain error tolerance.
Fourth, the price , based on some special requirements of LED applications on flat panel lamps, multiple parameters should be basically the same, so that enterprises can strictly control and sort the LED device for LED panel lamps, increasing the production process. Manufacturing costs, the recent replacement of traditional grille lamps in the near future does not have a price advantage. Despite the above-mentioned technical problems that need to be solved, it is believed that the LED panel light will surely be an area where performance is constantly improving and new products are constantly innovating.
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