High-Power LED Light Sources for Optical Measurement Systems Operated at Continuous and Overdriven Pulsed Mode

Abstract

The rapid progress of light emitting diode (LED) technology has recently resulted in the availability of high power devices with light emission intensities comparable to that of visible laser light sources. On this basis two versatile devices have been developed, constructed and tested. The first one is a high-power single LED iiluminator that provides continuous light (CW) as weil as light pulses of programmable width and intensity. The apparatus can be used for both light field as weil as dark field imaging in high-speed videography and in image based measurement techniques such as PIV (particle image velocimetry), LPT (Lagrangian particle tracking), BOS (background oriented schlieren), IPCT (image pattern correlation technique), shadowgraphy and schlieren . The device generates extremely bright, non-coherent, but essentially monochromatic, light. The CW-intensity is up to 2100 Im and reaches 14,000 Im (528 nm) in overdriven (250 A) pulsed operation. Available colors are red (623 nm), green (528 nm) or blue (462 nm), UV (390 nm or 400 nm) and white light. The mode of operation and all parameters can be programmed over a USB interface and stored in an internal non-volatile memory. The pulse width can be set in the range from 50 ns up to 300 ms or switched into CW. The programmable delay allows the flashes to be precisely synchronized with camera triggers or other trigger sources by means of an external TTL-trigger signal input. The double pulse mode for PIV is also provided. The device is equipped with interchangeable projecting objective lenses providing a homogenous light spot of various diameters. Moreover the light can be coupled with the experimental set-up using light guides and accompanying optics, e.g. light sheet lenses.