Research on Light Performance Measurement Methods and Application Scenarios of LED Light Sources

Abstract

As a solid-state semiconductor cold light source, LED (Light-Emitting Diode) has become the mainstream in the lighting field due to its advantages of energy conservation, environmental protection, and long service life. The light performance of LED light sources, including luminous efficacy, luminous flux, beam angle, color temperature, and color rendering index, directly affects user experience. This study measures the main light performance parameters of various commonly used LED light sources and compares the measurement results. Based on the analysis of different application scenarios, appropriate LED light sources are recommended to provide references for practical applications. The research shows that point light sources, floodlights, wall washers, and street lights each have distinct performance characteristics, which determine their suitability for different lighting environments such as indoor lighting, industrial lighting, venue lighting, landscape lighting, and road lighting. With the continuous advancement of technology, LED lighting will play a more significant role in smart homes and healthy lighting.

1. Introduction

The development of lighting technology has undergone a profound evolution, transitioning from incandescent lamps, fluorescent lamps, and metal halide lamps to the vigorous development of LED technology. LED light sources have emerged as a highlight in the lighting industry, thanks to their outstanding energy efficiency, reliability, long lifespan, and environmental friendliness. They are widely applied in indicators, signal lights, displays, indoor lighting, road lighting, venue lighting, and landscape lighting. Unlike traditional light sources, LED light sources use solid semiconductor chips as luminescent materials. When carriers recombine in the semiconductor, excess energy is released in the form of photons, directly emitting red, yellow, blue, and green light. By applying the three-primary color principle and adding phosphors, LED light sources can produce light of any color.

The performance of LED light sources is crucial to their application effects. Key light performance parameters include luminous flux, luminous efficacy, light intensity distribution, color rendering index, and color temperature. Accurate measurement of these parameters is the basis for evaluating LED quality and selecting suitable products for specific scenarios. Currently, the main measurement methods for LED light performance are the integrating sphere method and the goniophotometer method. The integrating sphere method is strictly limited to small-sized LED point light sources due to requirements on the type and size of the measured light source, while the goniophotometer method is more widely used for other types and sizes of LED light sources. Previous studies have explored measurement methods, the advantages of near-field measurement in optical design, and the importance of light intensity distribution curves. However, there is a lack of in-depth analysis on the performance differences between various LED light sources and their practical application implications. This research aims to fill this gap by systematically measuring and comparing different LED types and matching them with appropriate application scenarios.

2. Light Performance Measurement Methods of LED Light Sources

2.1 Luminous Flux Measurement Method

Luminous flux refers to the amount of light emitted by a light source per unit time, usually expressed in lumens (lm). It is an indicator of the total light output of a light source, equivalent to optical power. A higher luminous flux means the light source emits more light, directly affecting the human eye's perception of brightness and serving as a key parameter for evaluating overall brightness. In practical applications, luminous flux is a critical factor in LED selection: high-luminous-flux sources are suitable for providing strong illumination, while low-luminous-flux sources are ideal for local or low-illumination areas.

According to the measurement method specified in GB/T 24824-2009 "Test Methods for LED Modules for General Lighting", the luminous flux measurement is conducted in an optical darkroom. The tested LED light source or luminaire is installed at the rotation center of a goniophotometer and powered on to operate under specified conditions. A rotating arm drives the light source or luminaire to rotate around its vertical axis, forming a virtual spherical surface. The goniophotometer's photometric detector measures the illuminance at various points on this virtual sphere, ensuring sufficient sampling on multiple light-emitting planes with small angular intervals. The distance between the photometric detector and the luminous center of the tested object serves as the radius of the virtual sphere. Typically, the angular interval between planes is 5°, and the interval within each plane is 1°. For light sources or luminaires with large sizes or narrow beam angles, smaller intervals are adopted to ensure the integrity of illuminance distribution sampling.

Since the measured illuminance is proportional to the light intensity of the source in that direction, the goniophotometer automatically integrates the illuminance over each tiny surface element on the sphere to calculate the luminous flux. The total luminous flux is computed using the numerical integration method as shown in Formula (1):

Φtot​=∫(SM​)​EdS=∫04π​r2E(ε,η)dΩ=∫02π​∫0π​r2E(ε,η)sinεdεdη

Where Φtot is the total luminous flux (lm), r is the radius of the virtual sphere (m); SM​ is the surface area of the virtual sphere (m²); and (ε,η) represents the spatial angle.

2.2 Measurement of Light Intensity Distribution and Beam Angle

Light intensity distribution describes the intensity of light emitted by a source in different directions. By detecting light intensity distribution data under specific installation conditions, the uniformity of illumination and effective coverage area can be evaluated, which is of great significance for various application scenarios such as home lighting, commercial lighting, and industrial lighting. The beam angle refers to the divergence angle of the light emitted by the source, directly affecting the concentration and diffusion of the lighting effect, thus determining its applicable occasions. These two parameters are crucial for the market application of LED light sources.

During measurement, the distance between the detector and the tested object must be at least 5 times the maximum luminous opening area of the object, considering the luminous area, light intensity, and beam angle of the LED light source or luminaire. The tested object is placed on a rotating frame of the goniophotometer that can rotate around two axes. On the characteristic luminous plane of the LED, a point luminance meter or spectral radiometer is placed in the far field to collect far-field light intensity data. The measurement interval is no larger than 1/20 of the half-peak beam angle. For measurements with a beam angle less than 10° or strict requirements on direction angles, lasers or more effective methods are used to install and align the initial position of the tested object. As the light source rotates around two axes, data from the entire surrounding space is collected to generate light intensity distribution curve data, based on which the half-peak beam angle is calculated.

The dual-mirror goniophotometer measurement method specified in GB/T 24824-2009 places the tested object at the rotation center of the dual-mirror goniophotometer, which only rotates around its vertical axis. A rotating reflector rotates around the tested LED light source or luminaire, reflecting the light beam measured in a certain direction to a second reflector at a distance, which then reflects it to the optical detector. This method keeps the tested LED in a stationary operating state, offering advantages of high measurement stability and small system space occupation.

3. Comparison of Light Performance Measurement Results of Different LED Light Sources

Using the standard measurement methods mentioned above, the main light performance parameters (luminous efficacy, color temperature, color rendering index, and beam angle) of different types of LED light sources were measured. The specific results are shown in Table 1.

Table 1: Light Performance Measurement Values of Different LED Light Sources

Currently, LED light sources adjust their light intensity distribution mainly through the shape and transmission performance of the translucent cover wrapping the light-emitting diodes. Each type of LED light source has a unique light intensity distribution pattern. Point light sources, with their small size, exhibit a wide half-peak beam angle range and high color rendering index, indicating their ability to provide uniform and natural lighting. Floodlights feature high luminous efficacy and a narrow half-peak beam angle, demonstrating strong focusing capabilities and excellent illumination performance, making them suitable for long-distance and concentrated lighting. Wall washers have balanced performance parameters, with strong spatial layering and three-dimensionality of light, which is ideal for contour lighting. Street lights stand out with high luminous efficacy and a wide beam angle range, enabling them to deliver bright and uniform illumination over large areas.

4. Requirements for Light Performance in Different Application Scenarios

LED lighting has a wide range of application scenarios, including indoor lighting, industrial lighting, venue lighting, landscape lighting, and road lighting in daily life and work. Different application scenarios have distinct requirements for light performance based on design objectives and user needs, as detailed in Table 2.

Table 2 Requirements for Light Performance in Different Application Scenarios

By analyzing the light performance requirements of different application scenarios and combining them with the characteristics of various LED light sources, the following matching recommendations are proposed:

Indoor Lighting: LED point light sources are suitable for various indoor locations that require precise lighting positioning. Their high color rendering index (Ra = 86.0) ensures that objects appear true to their original colors, while the wide beam angle (around 119°) provides comprehensive coverage, making them ideal for homes, offices, commercial spaces, and factories.

Venue Lighting: LED floodlights and point light sources are recommended for stadiums, stages, exhibition halls, and museums. Floodlights offer high luminous efficacy (135.1 lm/W) and strong directional illumination, which can meet the high-brightness requirements of large venues. Point light sources, with their excellent color rendering, are suitable for exhibition halls and museums where color accuracy is crucial.

Landscape Lighting: LED wall washers are the preferred choice for building lighting, decoration, and indoor atmosphere creation. Their long strip shape, balanced luminous efficacy (96.1 lm/W), and rich color options allow them to outline architectural and landscape contours effectively, making them suitable for exterior wall lighting of single buildings and historical building complexes, as well as green landscape lighting and billboard lighting.

Road Lighting: LED street lights are specifically designed for urban arterial roads, secondary roads, rural roads, industrial parks, squares, and scenic areas. With the highest luminous efficacy (149.7 lm/W) and a wide beam angle range (149.4° in the C0/180° plane), they provide uniform and bright illumination, ensuring traffic safety for vehicles and pedestrians and meeting the visual needs of people's activities.

Industrial Lighting: A combination of LED point light sources and floodlights can be used to achieve balanced illumination in workshops and warehouses. Point light sources ensure uniform lighting in large areas, while floodlights can focus on work surfaces that require higher brightness.

5. Conclusion

Compared with traditional lighting technologies, LED light sources offer higher energy efficiency, longer service life, and better environmental performance. Their flexible temperature and color adjustment functions make them the optimal solution for smart home lighting applications. This study systematically measures and compares the light performance parameters of different types of LED light sources, including point light sources, floodlights, wall washers, and street lights. The results show that each type of LED light source has unique characteristics in terms of luminous efficacy, color temperature, color rendering index, and beam angle, which determine their suitability for specific application scenarios.

LED point light sources, with their high color rendering index and wide beam angle, are suitable for indoor lighting in homes, offices, commercial spaces, and factories. LED floodlights, featuring high luminous efficacy and strong directional illumination, are ideal for venue lighting such as stadiums and exhibition halls. LED wall washers excel in landscape lighting and architectural decoration due to their balanced performance and contouring capabilities. LED street lights provide reliable and efficient lighting for various road types, ensuring traffic safety.

With the continuous advancement of technology and the reduction of costs, LED lighting technology will become more popular. In the future, LED light sources will play a more important role in smart homes, healthy lighting, and other fields, bringing high-quality lighting environments to more people. Further research can focus on optimizing measurement methods to improve accuracy and exploring the application of LED light sources in emerging fields such as healthy lighting and smart cities.

References

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