High-brightness source based on luminescent concentration

Abstract

The concept of a high-luminance light source based on luminescent conversion of LED light and optical concentration in a transparent phosphor is explained. Experiments on a realized light source show that a luminous flux of 8500 lm and a luminance of 500 cd/mm² can be attained using 56 pump LEDs at 330 W electrical input power. The measurement results are compared to optical simulations, showing that the experimental optical efficiency is slightly lower than expected. The present status enables applications like mid-segment digital projection using LED technology, whereas the concept is scalable to higher fluxes.

Extraction optics for high lumen density sources

“…Simulations were performed using LightTools raytracing software ( [1], https://www.synopsys.com/opticalsolutions/lighttools.html). The LEDs are approximated by simple rectangular sources with a Lambertian distribution.…”

“…The mentioned conversion efficiencies have been determined in an integrating sphere (Instrument Systems) by separate measurements of the blue flux from the LED module and the green flux from the complete HLD module (at the same input electrical power). More details on the set-ups for the experimental results, as well as on the module construction, can be found in literature [1][2][3][4][5].…”

“…The main reasons for this relatively low conversion efficiency were discussed before [1,4] and will be repeated briefly here. Firstly, the injection of blue pump light is not fully efficient since part is reflected and part is transmitted.…”

“…Moreover, both discharge lamps and laser-based sources degrade relatively fast. Recently [1][2][3][4][5], we developed a new type of LED-based light source, the high lumen density (HLD) source, which is very stable and enables the mentioned applications (luminance > 2·10 9 cd/m 2 ). Similar concepts were investigated by others [6,7].…”

“…The red dashed line shows the simulated output spectrum, obtained from ray-tracing simulations [1,4] using the measured absorption (blue) and emission (orange) spectra as input. The simulated value for the conversion efficiency is 0.29, slightly more than the experimental value.…”