The left figure illustrates Helm Scientific's low-leakage current and high-responsivity light measurement capabilities. The I-V curve (blue line) of a commercial green LED was measured by sweeping forward bias while recording electric current. Simultaneously, a fraction of emitted light power (~3.7%) was detected by a Si photodiode probe positioned ~5 mm away (red line). Obviously, light emission starts at ~1.7 V forward bias where non-radiative recombination current has already increased from ~20 pA to ~20 uA. The L-I-V plot from the same set of data is shown in the right figure. Approximately, the detected light power is proportional to the LED forward current (green line). The LED turn-on voltage of ~1.8 V can be extracted by the linear regression of post-turn-on V-I data (black line).
