Conventional halogen and metal halide light sources produce highly directional beams that many architects and lighting designers rely on, but with lower efficiency and shorter lifetimes than LED. And while LEDs are highly efficient with longer life, beam angles less than 10° are challenging to produce from compact luminaires. Today, laser diodes are attracting interest as efficient, highly collimated white-light sources, with great potential in architectural lighting and beyond.
The first commercial laser lighting source on the market uses the same principle as most LEDs in architectural lighting: blue light excites phosphors producing broad-spectrum white light. But using the laser diode, these surface-mount devices (SMDs) currently offer luminances 10 times higher than the most–lumen-dense LEDs on the market. The automotive industry is embracing laser diodes as smaller, more efficient headlights with impressively long throw. Note that non-phosphored, multi-chip RGB laser technologies are also progressing, making early inroads in the display and biotech industries.
Tiny laser diodes are the most common form of laser, and are found in barcode readers, laser pointers and DVD players. To produce white light, a high-power blue indium gallium nitride (InGaN) semi-polar laser diode excites a very small phosphor target (approx. 300 μm diameter) that converts the laser light to a broad spectrum. Eye safety is a concern and non-transmissive phosphors help ensure that none of the light comes directly from the laser.
Highly directional illumination – less than 2 degrees of divergence from 1 inch–diameter optics – is the result. At about 500 lm of output, the overall lumens-per-watt efficacy of laser diodes is currently lower than LEDs. However, the illumination on the target area per watt of power consumption (consider candelas per watt) is much higher. And unlike LEDs, laser diodes do not suffer from droop – the drastic reduction in efficiency that occurs with increasing drive currents.
At Light + Building 2018, more than 2700 exhibitors showcased the latest technologies applied to lighting, electrical engineering and smart buildings. For the first time, the event included lighting fixtures and other products implementing laser light technology. SoraaLaser (now SLD Laser) won the Design Plus Award, among 39 total winners. Two applications are shown above: a compact spot fixture from Targetti and an architectural fiberoptic system, where the highly directional laser diode enhances the efficiency of light injection into the fibers.
Another system demonstrated at the event was a small luminaire in which the beam angle is controlled electronically. This was achieved in partnership with Lens Vector and their liquid crystal lens technology that works in a complementary way with the collimated beam from the laser light system. The images below show the light pattern at different angles between dynamic changes.
Laser lighting is attracting significant interest in the architectural lighting community and in specialty applications. Development is ongoing to integrate directional white-light laser sources into next-generation lighting applications such as smart lighting, LiFi (light-based wireless data transmission), and the Internet of Things.