Although LED technology is still in the emerging phase, a technology even more advanced is already coming online: headlamps using blue laser diodes to excite remotely-placed phosphors as the light source. This report describes the current status of this exciting new technology development in its present nascent phase.
The basic light source unit is a blue laser diode focused on a yellow phosphor target. The laser diode “pumps” (excites) the phosphor and the combination of laser diode radiation and phosphor emission generates white light. This technique is called LARP (Laser-Activated Remote Phosphor) or LIPS (“Laser-Irradiated Phosphor Source). The white light output can then be shaped by optics to create the required beam characteristics. Key technology carriers of such a LIPS based lighting system are the blue laser diode, the laser optics for focusing on the phosphor target and the phosphor itself.
Main driving forces behind the development of such systems are the extraordinary high luminance and the possibility of modulating the beam photometry dynamically by scanning the laser beam. The high luminance allows very compact optical cavities for shaping the output beam. Furthermore the collimated laser diode beam can be scanned over the phosphor target to create variable spatial and time dependent beam patterns, i.e. adaptive headlighting systems.
LIPS technology is already used commercially in multimedia projectors and medical endoscopy, and shows fast growth. These application areas are driving R&D and investment for the system components and architecture.
The technology of laser-based headlight systems is presently in the very early stages of development and deployment, starting with the BMW i8 concept shown at IAA 2011 with a laser headlamp prototype. Since then, R&D by the industrial side and also universities has grown significantly. As a result, contributions on laser-based headlights have steadily increased at conferences and events. Several lighting companies and universities have shown photographs or even hardware of their technology demonstrator setups. Styling goals include headlamps with cavities as low as 10 mm height. Looking to next steps, the laser scanning technology could enable cost-effective and compact variable beam functionality like e.g., ADB.
From the OEM side, BMW have presented their “High Beam Booster” system on the i8 at IAA 2013 as a first concrete application of laser technology, with a market launch expected for the end of 2014. Another interesting move comes from the Japanese industry: Stanley and SIM-Drive have equipped a street-legal electric concept vehicle, the SIM- CEL, with a combined laser/LED system for real-life road testing.
Two other important topics are the regulation and standardisation of laser-based headlight systems, and safety issues unique to laser systems. Initial investigations suggest existing regulatory frameworks can be used for homologation. Nevertheless, industrial standardisation of components even in an early phase would make sense.
As with every new technology, there are still significant technical and commercial uncertainties. Technical issues e.g., include temperature sensitivity of the laser diodes and high requirements for their drive electronics. And a reliable cost roadmap for laser diodes and related electronics and optics will be necessary for commercial success.
In general, it is expected that laser-based headlight systems will enter the market due to their unique features and possibilities. Open key questions are how fast this will occur and whether this market entrance will be in competition or in co-existence with LED systems.