Hangzhou Yuanfang Optoelectronic Information Co., Ltd. ()
　　
Abstract: Total luminous flux is an extremely important indicator for evaluating LED products. However, the special properties of LEDs pose a challenge for accurate measurement of total luminous flux. Based on the characteristics of LEDs, this paper analyzes the advantages and disadvantages of the existing LED total luminous flux measurement methods and equipment, introduces the new developments of several internationally renowned laboratories in the field of total luminous flux measurement, and details the total luminous flux of LEDs in China. Benchmarking methods and advanced equipment. China's GO-R3000 2M2D dual-mirror distribution photometer with many core technology patents has been highly praised by international photometric experts for its excellent performance. Since its introduction, the products have quickly gained the favor of international high-end customers and become multiple LEDs. Standard measuring equipment for high-end laboratories.
Keywords: light effect total luminous flux distribution photometer integrating sphere
I. LED characteristics and challenges of total luminous flux measurement
As we all know, LED has the following unique luminescent properties:
LED products are very sensitive to temperature; LED products are generally narrow in beam size, and usually use a light source and luminaire integrated design, traditional relative measurement is no longer applicable, and absolute luminous flux and light intensity distribution measurement requirements and equipment are higher; LED The luminescence of the product has obvious spatial color unevenness and the like.
Due to the special luminescence properties of LED products, the accurate measurement of the total luminous flux is extremely challenging, and the lateral comparability of LED products is still not ideal. The total luminous flux measurement of LED products has become a key concern in the research and formulation of relevant standards in various countries.
two. Method and apparatus for measuring total luminous flux of LEDs
2.1 The challenge of accurately measuring LED luminous flux using an integrating sphere system
The integrating sphere system has been known for measuring total luminous flux. However, in the integrating sphere system, there is a big difference between the spectral distribution of the LED product and the spatial light intensity distribution and the common standard lamps, which will bring a large measurement error. The use of similar LED products to calibrate the integrating sphere system can greatly improve the measurement accuracy, but requires a more accurate total luminous flux measurement method and equipment as the benchmark for the transmission of LED products.
2.2 Distribution photometer to measure the total luminous flux of LED
The distribution photometer measures the light intensity or illuminance distribution of the LED product in space, and obtains the total luminous flux by integrating the whole space. According to the measurement optical path arrangement, it is divided into the light intensity integration method and the illumination integration method. The distributed photometer system has no special restrictions on the shape, size and beam angle of LED products, but it is critical to maintain the temperature stability of the LED products themselves.
2.2.1 Light intensity integral method: central rotating mirror type photometer
The central rotating mirror-type distribution photometer has been around for decades. As shown in Figure 1, the LED product under test must be rotated synchronously around the mirror in a relatively large spatial range. In addition to the inevitable synchronization error, the temperature of the LED product under test in the distribution photometer has great instability: in the darkroom, there is often a phenomenon that the upper temperature is high and the lower temperature is low, and the temperature difference is generally 2 to 5 °C. The LED product under test actually works in an alternating ambient temperature, and the larger the operating space, the greater the temperature difference;
The LED product under test produces airflow during motion, causing a large change in surface temperature, which is further exacerbated by thermal inertia. The measurement error caused by these unstable factors varies with the design of LED products. In severe cases, it can reach more than 5%, plus the principle error that can not be avoided by the central mirror [4], and the total luminous flux measurement can reach 10 More than % error.