Study Of Thermal Stability Of LED Light Source Used For CCD Calibration

With wide application of CCD (charge-coupled device) cameras, techniques of CCD calibration become one of important issues in CCD devices'manufacture and research. Since there is no any needs to concern issues around the influences such as distortion, noise level, linear space-invariant etc when CCD devices can be considered as an idea one. In fact the CCD's characteristics keep changing all the way, for example its output can not keep stable when it is used to observe a uniform target. Even this target has a perfect Lambert character because of CCD's non-uniformity. With rapid development of techniques of CCD's manufacture and applications, it put forward higher requirements in CCD camera calibration technique. Standard light source must have the properties with uniformity and higher brightness. These topics were as the research background.In this paper, it was discussed CCD calibration problems at first. Then it introduces the principle of CCD, the parameters and calibration methods. It introduces the main problems of CCD non-uniformity calibration in the light. Second, it introduces LED characteristics, advantages and shortcomings. The standard light source with LED has volume of small and compact. It has characteristics such as multi-level flux adjustment, color temperature compensation when LED is working in cascade. LED becomes one of the best sources for CCD calibration. As a standard light source the stability and uniformity is one of the key parameters. Where as LED is sensitive to the ambient temperature,the power supply and voltage fluctuations when the output of LED is in high luminous flux. The temperature of LED will increase quickly at this case. It also leads to the shift of LED's peak wavelength decreasing LED's light efficiency,life-circle and reliability. So the junction temperature is the main problems that constraint to the development of LED. At present positive voltage is widely used in junction temperature measurement, But it is used Single LED. Firstly, LED Thermal stability was detected with the gradient of temperature measurement in the condition of 2x2,4×4 array. The following conclusions are listed as follows:1) with the current increases, the temperature of the cascade LED will rapidly increase; 2) The designing of LED heat sink with 2×2, 4x4array was finished.3) The stability testing of LED array by using the luminous flux measurement system had been implemented. The results shows that LED with the appropriate heat sink can work well when the current source power is used, it can meet the requirements of thermal stability.Testing of LED's thermal stability, techniques and methods are introduced in this paper. The temperature around the center of 2×2,4×4 array was measured by means of temperature gradient testing. The LED flux is stable above 0.5 when a suitable heat sink is selected. Therefore, LED light source can be used for CCD calibration standard source.