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Optical Tests

Forward current biasing is also used for optical tests because electrical current flow is closely related to the amount of light emitted. Optical power can be measured by placing a photodiode or integrating sphere close to the device under test to capture the emitted photons. This light is then converted to a current, which is measured using an ammeter or one channel of a source-and-measure instrument.

光学测试

正向偏置电流也用于光学测试[1]，因为电子电流与发光的强弱密切相关。通过在待测器件附近放一个光电二极管或者累计球捕捉发出的光子可以测出光强度（optical power）[2]。然后将光转换成电流，利用安培计或者源测量仪器的一个通道测量电流的大小。

In many test applications, the voltage and light output of the diode can be measured simultaneously using a fixed source current value. In addition, details such as spectral output can be determined from the same drive current value by using a spectrometer.

在很多测试应用中，二极管的电压和发出的光可以利用大小固定的电流源同时测出来。此外，利用分光计可以在同样大小的驱动电流下测出诸如光谱输出之类的详细参数。

Reverse Breakdown Voltage Test
Applying a negative bias current to the LED will allow probing for the reverse breakdown voltage (V_R). The test current should be set to a level where the measured voltage value no longer increases significantly when the current is increased slightly more. At levels higher than this voltage, large increases in reverse bias current result in insignificant changes in reverse voltage. The specification for this parameter is usually a minimum value. The V_R test is performed by sourcing a low-level reverse bias current for a specified time, then measuring the voltage drop across the LED. The measurement result is typically in the range of tens of volts.

反向击穿电压测试

对LED加载一个反向偏置电流可以测出反向击穿电压（V_R）[3]。测试电流的大小应该设置为当电流稍微增加时测出的电压值不再明显增大的位置。当电压高于这个电压值时，反向偏置电流的大幅增加导致反向电压变化不明显。这个参数指标通常是一个最小值。在测试V_R时要在一定的时间内加载一个小的反偏电流[4]，然后测量LED上的电压降。测量[5]结果的大小范围通常为几十伏。

[1] 光学测试：http://www.keithley.com.cn/products/localizedproducts/opto

[2] 光强度：http://www.keithley.com.cn/products/localizedproducts/localizedproducts/2004_china_catalog.pdf

[3] 反击穿电压：http://www.keithley.com.cn/re/cel

[4] 内部偏移：http://www.keithley.com.cn/llm/a/31.html

[5] Source meter Solution: http://docs.google.com/viewer?a=v&q=cache:jxbedtXGJZcJ:www.keithley.com.cn/data%3Fasset%3D54937+LED&hl=zh-CN&pid=bl&srcid=ADGEESgvqI7PSfdlWCLGf72-g32xkt2xthj29V_wk6Qjfy3_HgTAP6jVur4Fz5wlOZF1U5oWnBGd9H20GIIC3AWNH0lW4HZ3mpArydiuB9y3aAuoJ2oXB2gKWH5IU1NeaiThR9APG9aQ&sig=AHIEtbQk8E2kc00jVseAI4Ooc1VNIEUL-g