Measurement Approach for Monitoring Time-Dependent Intensity Variations of Commercial Light Sources

Abstract

This work presents a flicker measurement approach to record spectrally resolved emission intensity variation over time in a single measurement run. This approach supplies the percent flicker, the flicker index and additional information such as the color point shift, the color rendering index (CRI Ra) and the color temperature (CCT) of a luminaire over time. Using this technique, it is feasible to derive the impact on the flicker behavior of different activator ions and their decay behavior in a respective luminescent material as function of time. Commercial luminaries for general lighting such as halogen lamps, compact fluorescent lamps, light emitting diodes (LEDs) and filament LEDs comprising an E27 or E14 socket were tested to demonstrate the possibilities of this technique. The derived data are plotted in a 3D-Plot depicting the photoluminescence intensity (z-axis) over time (x-axis) and wavelength (y-axis). Percent flicker, flicker index, color point shift and CCT over time are calculated from the same data set and presented for each luminary. The CRI (Ra) is calculated for those luminaries with constant emission. Depending on the type of luminary, its type of luminescent material (type of activator ion), and driver system, a color point shift was monitored and discussed in detail.