Low frequency noise and long-term stability of noncoherent light sources

Low frequency fluctuations in light intensity were measured from five different types of commercially available light emitting diodes with wavelengths from 375 nm to 740 nm and from two different halogen lamps. At low frequencies below 10–100 Hz some light emitting diodes (LEDs) can provide lower levels of noise than halogen lamps. A noise quality factor β is proposed in order to characterize noise behavior of LEDs.