With the continuous improvement of LED chip efficiency, packaging technology, and LED lighting fixture heat dissipation technology, LED light sources have rapidly expanded in the field of lighting, and the LED panel light industry is booming.
LED panel lighting fixtures have many advantages such as uniform light emission, low glare, and easy installation. They have good market development prospects and lead the new trend of modern and fashionable indoor lighting. However, currently, the quality of LED panel lights on the market is uneven, and some manufacturers ignore product quality, blindly lowering prices and engaging in vicious competition, which seriously affects the healthy development of the industry.
Since there is currently no national standard for LED panel lights, in 2014, the China Electronics Industry Standardization Technology Association announced the cross-strait common standard “LED Panel Lighting Fixtures for Indoor General Lighting.” The standard stipulates safety and performance requirements for LED panel lights, regulates the quality requirements of LED panel lights, and serves as a reference for manufacturers of panel lights, also enabling market management to have legal basis. Referring to the requirements of the cross-strait common standard, the following is a discussion on how to control the quality of LED panel lights.
What is LED Panel Lights
An LED panel light is a type of lighting fixture that uses light-emitting diodes (LEDs) to provide illumination. LED panel lights are typically flat, thin, and rectangular in shape, and are designed to be mounted on ceilings or walls. They are commonly used in commercial and residential settings, such as offices, schools, hospitals, and homes, to provide energy-efficient and long-lasting lighting. LED panel lights are known for their high luminous efficacy, which means they produce more light per watt of power consumed than traditional lighting sources, such as incandescent or fluorescent lights. They also have a longer lifespan, require less maintenance, and are more environmentally friendly than traditional lighting options.
Structural Characteristics
LED panel lights have unique structural characteristics compared to other lighting fixtures. They mainly consist of a light source, a light guide plate, a diffusion plate, a reflector, a driver power supply, etc., adding structures similar to LED backlight products such as light guide plates, diffusion plates, and reflectors that other lighting fixtures do not have.
(1) LED Light Source
LED panel light manufacturers basically use SMD chip series for LED light sources, such as 3528, 3014, etc. LED panel light manufacturers face a dynamic market and will choose light sources that meet design requirements according to the actual needs of customers. The selection of LED light sources is extremely critical to improve product performance and is one of the important factors to improve the quality of LED panel lights.
(2) Light Guide Plate
The light guide plate is used to convert the light emitted by the LED point source into a surface light source through optical technology, and the side LED light is refracted through dot matrix to guide the light uniformly from the front. Currently, the main form of light guide plate used is the printed light guide plate. The quality of the light guide plate will directly affect the brightness and uniformity of the product, and it is required to have good light transmittance.
The light guide plate is a key point for quality control of LED panel lights. If the dot matrix design is not good, the overall light efficiency obtained will be poor, and there will be uneven light output, such as bright in the middle and dark on the sides, bright light bands at the light entrance, visible dark areas, and inconsistent brightness at different angles. To improve the light efficiency of the light guide plate, the dot matrix design is mainly relied upon, followed by the quality of the plate material. High-transmittance qualified plate materials should be selected.
(3) Diffusion Plate
The main function of the diffusion plate is to uniformly guide the light from the light guide plate out and make the light distribution more uniform. When the light beam reaches the diffusion point, the reflected light will spread to various angles and then be emitted from the front of the light guide plate. By using various dense and different sizes of diffusion points, the light guide plate is uniformly illuminated, and the brightness of the light guide plate is improved. It can also play a role in blurring the dot matrix.
The diffusion plate generally uses acrylic 2.0 or PC material, and the poorer one is PS material. Acrylic has a lower cost and a slightly higher light transmittance than PC, but weaker aging resistance; PC is slightly more expensive but has stronger aging resistance. After the diffusion plate is installed, the dot matrix should not be visible, and the light transmittance should be around 90%. The light transmittance of acrylic is 92%, PC is about 90%, and PS is about 88%. Manufacturers can choose the diffusion plate material according to their needs. Currently, most manufacturers use acrylic materials.
(4) Reflector
The reflector is used to reflect all the light spilled out of the light guide plate, so that the light emitted by the LED can be fully utilized. As much as possible, a reflector with a reflectivity close to 100% should be selected to maximize light utilization and increase the output brightness of the LED panel light. Generally, it is RW250.
(5) Back Cover Plate
The main function of the back cover plate is to seal the LED panel light, generally using aluminum plate, which can also play a role in heat dissipation.
(6) Driver Power Supply
Currently, there are two types of LED driver power supplies. One is to use a constant current power supply, which has high efficiency and a PF value of up to、
Efficacy improvement
Efficacy is an important indicator to evaluate the performance of LED flat panel lights. Luminous efficacy is the ratio of the luminous flux emitted by the light source to the electrical power it consumes, in lm/W. Luminaire efficacy is the ratio of the initial total luminous flux emitted by the luminaire to the power it consumes, in lm/W, under the claimed conditions of use of the luminaire.
（1）Luminous efficacy
“Luminaire efficacy” is used to evaluate LED light source, “luminaire efficacy” is used to evaluate LED lamps, LED light source luminaire efficacy and LED luminaire efficacy both indicate the efficiency of electrical energy into light energy, is to describe the energy-saving characteristics of lighting products indicators, but their connotations are different The meaning is different. LED flat panel luminaire for indoor general lighting” standard, the measurement should be carried out in a convection-free environment with relative humidity not exceeding 65% and temperature of 25℃±1℃, and the LED flat panel luminaire should be in stable working condition.
(2)LED light source luminous efficacy
LED light source luminous efficacy in the light source luminous flux is the bare light source (not yet installed into the state of the luminaire) emitted luminous flux.
(3)LED luminous efficacy
LED luminous efficacy in the molecular luminous flux is the light source into the luminaire, while using the required LED control device or LED control device power, the luminous flux emitted by the luminaire. LED light source consumes less electrical power than the LED luminaire consumes electrical power.
(4)LED VS LED luminous efficacy
LED light source luminous efficiency is much greater than the luminaire efficiency. One is because the LED into the luminaire, the color temperature increases, the light output is reduced; the second is because the light source into the luminaire, the use of LED control device or power supply after the existence of system losses; third is the loss of light through the optical system of the luminaire, the above factors will cause the luminous efficiency of the luminaire reduced. GT004-2012 “indoor general lighting with LED flat lamps “The standard specifies the efficiency level of the luminaire with different color temperature (the following table).
(5)How to improve the luminous efficacy of LED panel Light
a. Choosing High Luminous Efficiency and High Brightness LEDs
To improve the efficiency of LED flat panel lights, it is important to choose LEDs with high luminous efficiency and high brightness. This not only improves the efficiency and reduces costs but also enhances the quality of the LED flat panel light.
b. Maximizing Light Utilization
To effectively improve the utilization of light and enhance the effectiveness of LED flat panel lights, it is essential to focus not only on the brightness of the LED but also on the design of the light path. The light emitted by the LED should be fully utilized from the LED light source to the light guide, reflective plate, and final display output.
c. Choosing Good Quality Light Guide Plate and Reflective Materials
The light utilization rate of LED flat panel lights from the light guide to the final output display is less than 70%. To improve the light utilization rate, it is crucial to choose good quality light guide plate and reflective materials that meet the LED flat panel light design technical performance indicators and size specifications.
d. Importance of Light Guide Plate
The light guide plate plays a crucial role in guiding the light scattering direction, improving the brightness of the panel, and ensuring the uniformity of the panel brightness. As the trend is towards light and thin aesthetics, most of the LED flat panel lights are now designed with side-light modules, which require a good quality light guide plate.
e. Quality and Thickness of Light Guide Plate
The quality and thickness of the light guide plate have a significant impact on the quality of LED flat panel lights. The light transmission rate and optical uniformity index of the light guide plate are the key factors in improving the efficiency of side-light LED flat panel lights.
f. Construction of Light Guide Plate
The light guide plate is constructed using an injection molding method of acrylic pressed into a smooth surface plate or using a ready-made acrylic plate. The light transmission rate of the light guide plate is more than 90%. Highly reflective and non-absorbent material is used at the bottom side of the light guide plate with screen printing on the diffusion point. A reflective paper is used to fully reflect the light back into the light guide plate, thereby improving the use of light efficiency and front brightness.
g. Performance of LED Flat Panel Lights
After laboratory tests, it was found that LED professional manufacturers of LED flat panel lights can reach 110 lm/W at a color temperature of 5500K. However, not many manufacturers can reach the first level of performance. It is important to choose a reliable and experienced manufacturer to ensure high-quality LED flat panel lights.
Excellent uniformity
Another important indicator of LED flat panel lamp is its luminance uniformity, LED flat panel lamps for indoor general lighting” proposed luminance uniformity requirements, refers to the minimum luminance on the luminous surface of the lamp and luminance arithmetic The ratio of the average value of the luminance.
(1)Test method
As a LED flat panel light, the unevenness of the luminance will lead to the uniformity of the panel display brightness, resulting in uncomfortable perception of the human eye. According to standard, the brightness uniformity of LED flat panel luminaire 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.
Square side length L, rectangular long side L and circle diameter D is not greater than 20cm LED flat panel luminaires, according to the requirements of the following figure (a) point; greater than 20cm LED flat panel luminaires according to the requirements of the following figure (b) point. In the LED flat panel luminous surface of the test spot diameter of 2cm ~ 3cm, the luminance value of each point and the average luminance subtracted to take the maximum value, and then the maximum value divided by the average luminance to take the percentage that is the luminance uniformity. It is generally believed that the uniformity of performance of more than 80% of the human eye perception is not significant.
(2)Brightness uniformity test
Flat panel luminaire brightness uniformity test is the first time in the standard requirements for the surface brightness of indoor lamps and lanterns. It reflects the characteristic parameters of flat panel luminaires, which is one of the important features of this type of luminaire. In indoor lighting, surface luminous lamps and lanterns to create a soft and simple lighting effect can not be replaced by other bracket luminaires or grille luminaires.
(3)LED Panel Light VS Fluorescent lamps
Indoor lighting, with diffusion plate fluorescent lamps and lanterns are also with surface luminous effect, has been used for many years, but can not reach the level of brightness uniformity of LED flat panel luminaires. The reason is that fluorescent tubes are omni-directional light source, can no longer adjust the optical system to achieve better brightness uniformity, and lighting efficiency is 40lm / W level. The light source of LED lamps and lanterns is half-space luminescence, in the lamps and lanterns, the light utilization rate is high, the efficiency of the lamps and lanterns can reach more than 80lm/W, while the brightness uniformity can reach a higher level.
(4)Light guide structure
Using side light guide structure LED flat panel lights, LED light-emitting tubes are arranged on the side of the light guide, the visual effect of the lamps and lanterns is better. Most domestic manufacturers are still using printed light guide plate as the light guide component, using a variety of sparse, different sizes of diffusion points, so that the light guide plate uniform light to obtain a good luminous uniformity.
(5)Results
From the test results, small size LED flat panel light brightness uniformity is easy to meet the requirements, even if the uniformity of a little deviation, the human eye is not easy to feel it. Larger area LED flat panel lights, sometimes due to the quality of the light guide plate brightness unevenness, there are process reasons for the above-mentioned light into the light at the bright band, or visible local dark area phenomenon. Therefore, the selection of the main raw materials such as light guide plate, diffusion plate, and reflective paper to do a good job of quality evaluation, and in the raw materials into the factory to strictly check, manufacturers should be equipped with the necessary optical brightness meter and light transmission rate test instruments.
Controlling Color Differences in LED Flat Panel Lights
(1)Human Eye Sensitivity to Color Differences
The human eye is particularly sensitive to yellow and green colors, which means even slight fluctuations in these colors are noticeable. As a result, LED flat panel lights of different batches should not have obvious color differences, and users should be able to re-purchase the same color products if needed.
(2)Standards for Consistency
The standard for LED flat panel lights requires the light color between three randomly selected samples to be consistent, with the difference between the average color coordinate values not exceeding 0.004 in the CIE 1976 (u’v’) diagram. The chromaticity deviation from the initial value should also be within 0.007.
(3)Raw Materials and Color Control
LED flat panel lights commonly use red, green, blue, white, and yellow colors, with the unit of measuring color being nm (nanometer). To control color differences, manufacturers must control the raw material, particularly the LED light source. The wavelengths of different colors must be consistent to avoid color differences and uncertainties over time.
(4)Color Temperature and Consistency
For white light, color temperature is typically marked as warm white (3000-3500K), white (3500-5000K), or cold white (5000K-6500K). LED color temperature can vary by 500K or even 1000K, with packaging factory internal error requirements for color temperature typically being +/- 200K. Therefore, choosing a stable color LED light source and strict production process control is crucial.
(5)Causes and Solutions to Color Difference
Detection of LED flat panel lamp color differences has found that the main reason for differences is inconsistency in LED optical performance index due to poor LED light source screening during selection. To address this issue, supplier evaluation should be done, LED suppliers should be held to product consistency requirements, and LED incoming inspection should be strengthened to remove color differences beyond requirements.
Current Issues
Despite the constantly improving performance of LED devices and their expanding application scope, LED flat panel lights still face several issues.
(1)Low effectiveness
One urgent problem is to improve the effectiveness of low-side-entry LED flat panel lights. Increasing the number of chips to achieve high brightness results in poor energy-saving effects, especially for large-sized flat lamps. Increasing power also increases the working temperature of the LED module, affecting light decay and life. Therefore, choosing a high luminous efficacy of the LED light source requires comprehensive consideration.
(2)Inconsistency of light failure
The inconsistency of light failure between individuals in LED flat panel lights can cause brightness drop and unevenness. If using RGB color mixing LED flat panel lights, the different colors of LED light failure can also increase the possibility of unevenness. Sacrificing some efficiency and letting the LED work below the rated power is a better solution to extend the time and reduce light decay.
(3)Discrete LED device parameters
To achieve consistent brightness and color rendering in LED flat panel lights, each LED device’s current and voltage should be consistent, and their brightness and wavelength should also be as consistent as possible. The LED flat panel lamp should use screened LEDs, especially for luminous efficiency, luminous flux, main wavelength, color temperature, and voltage drop.
(4)Price
Meeting some special requirements for LED flat panel lights results in multiple parameters that need to be basically the same. This requires enterprises to strictly control, sort, and increase manufacturing costs, leading to a lack of price advantage over traditional grille lights.
Despite these technical problems, LED flat panel lights will continue to improve in performance, and new products will continue to innovate in the field.
