Experiments with light-emitting diodes

The radiant and luminous power spectra, efficiency, and luminous efficacy of commercially available light-emitting diodes (LEDs) are measured. The output radiant power is determined with a silicon photodiode from its typical spectral response. A calculation of the radiant power spectra and the luminous power spectra is demonstrated. The frequency response of the LEDs is determined in the range 10-107 Hz. For the white LED, the frequency response of the primary blue emission and the green-yellow phosphorescence is measured separately, and the phosphorescence time constant is estimated. The ratio h/e is estimated using the emission wavelengths and the "turn-on" voltages.