Nicola Trivellin, Ph.D, is a research fellow at University of Padova, Italy, His research is directed toward the study of compound semiconductor devices for solid state lighting with particular emphasis on processing, design and reliability. He is the general manager and Co-founder of LightCube SRL, a Padova University spin-off working on research, development and design of innovative LED based lighting systems specifically focused on the Human Centric Lighting philosophy.
Laser Lighting: Opportunities and Criticalities
With this work we report on experimental and simulated studies of Remote Phoshpor laser lighting systems. Solid State Lasers are becoming more and more interesting, thanks to two main benefits with respect to Light emitting Diodes: 1) improved efficiency at higher currents resulting in a substantially droop free operation, and 2) an improved optical management thanks to a reduced etendue. The combination of visible Blue (450nm) light and remote phosphor is a technology well known for LEDs, but finds application also for LD systems. In the latter case the radiation hits the phosphor with a much higher irradiance, thus locally increasing the temperature of the phosphor due to stokes shift losses and possibly causing some damages on the phosphor layer itself. Reliability therefore might be considered one of the major issues for these systems, in particular due to the more complex microelectronic structure of the Laser Diodes with respect to LEDs and their higher power densities. In this work we report on the stability of both blue high power laser diodes implemented in lighting systems and custom designed phosphor templates deposited on flat surfaces. The results of the stress tests report reliability issues at temperatures above 550°C and a strong dependency on the phosphor deposition methods and relative solvent involved in the deposition process.
In this work we also analyze the different possible design solutions to develop a laser lighting system. The structure of a Laser lighting system is dependent on whether the radiation passes through the phosphor deposited on a transparent substrate ( similar to LED mixing chamber solution )or is reflected from the phosphor itself deposited into a mirrored substrate. To demonstrate the performance possibilities of the Laser Activated Remote Phosphor technology we designed different optical test bench for both transmission and reflection setups. Results, although report an insufficient kuminous efficacy are interesting with respect to optical management and beam collimation with a 2° FWHM divergence angles from a LARP System based on 1’ optical elements.