Is laser diode expected to enter the lighting market?

- 2021-10-08-

Can semiconductor lasers be used for general lighting in the future? The energy efficiency of semiconductor lasers is 100 times or even higher than that of traditional LEDs, so it can provide very high light output with a smaller die size. For applications with limited physical size, the attractiveness of semiconductor lasers is obvious, but the disadvantage of using them for general illumination is that their emitting cavity is very narrow...

The working mode of LED and semiconductor laser (or laser LED) is basically the same, that is, when electrons and holes are polymerized, light is emitted, and the emission wavelength depends on the material used. The difference is that the spectral range of LED light is relatively narrow, while the light emitted by a semiconductor laser is basically a single wavelength. The emission wavelength of semiconductor lasers can range from infrared to ultraviolet, and has been widely used in optical fiber communications, barcode readers, optical disc readers, and laser printing. But so far, the application of semiconductor lasers in conventional lighting has proven to be impractical.
Like traditional lasers, semiconductor lasers also need resonant cavities for amplification. The resonant cavity consists of two parallel planes separated by a few hundred microns. These two planes act as mirrors and bounce the emitted photons back into the cavity. At low power levels, semiconductor lasers function similar to traditional LEDs. When the power is large enough (about 4kW/cm2), the photons ejected between the two "mirrors" start to stimulate the semiconductor material to emit more photons. When the generation of the laser light is offset and the internal loss exceeds the internal loss, the device starts to "laser", that is, emit a single wavelength of coherent light.

There are also some similarities between traditional LEDs and semiconductor lasers: both are powered by AC-DC drivers, and when the temperature rises, the light output will drop. But unlike traditional LEDs, semiconductor lasers do not seem to be affected by the Droop effect. The Droop effect increases the drive current, which results in lower power efficiency (output lumens/input watts). For lighting product applications, conventional blue LEDs have higher efficiency than semiconductor lasers, but only at lower input currents. Therefore, considering the required substrate area, it is not practical to generate the same level of light from a conventional blue LED.
Although laser diodes have appeared in the 1960s, they have only recently been energy efficient enough to be considered for lighting applications, especially for high-end automotive lights. BMW provided laser headlights and claimed that it is 10 times brighter than LED headlights and has a 30% higher efficiency. It uses a precisely placed reflector to reflect the blue semiconductor laser inside the headlamp housing to generate a white light beam, and then uses a phosphor-filled lens to focus it to produce high-intensity white light.
Can semiconductor lasers be used for general lighting in the future? The theoretical energy efficiency limit of phosphor-converted white light LED is about 350 lumens/W, while commercial lighting products are close to 200 lumens/W. The energy efficiency of semiconductor lasers is 100 times or even higher than that of traditional LEDs, so it can provide very high light output with a smaller die size. For applications with limited physical size (such as car headlights), the attractiveness of semiconductor lasers is obvious, but the disadvantage of using them for general lighting is that their emitting cavity is very narrow (only about 1 to 2 degrees).
At present, how many companies are committed to using semiconductor lasers for general lighting is still unclear, but at least one company has already provided related products. SLD Laser launched LaserLight surface mount (SMD) components as early as 2016. This component uses blue semiconductor lasers, phosphors and high-lumen packages. It can emit about 500 lumens of white light in a 7×7mm package, and it is not for the human eye. Damage, its sophisticated optical components achieve a beam angle of no more than 2 degrees. The LaserLight SMD component is the world’s first semiconductor laser light source to obtain UL 8750 safety certification.
The most likely situation is that laser semiconductors are first applied to lighting products for special buildings. These applications require narrow and high-intensity beams. For example, in museums, galleries, retail spaces and some other special places, only one corner of the space needs to be illuminated instead of the entire space. This is not only a need for space aesthetics, but also simplifies control and maintenance. However, due to the narrow beam of semiconductor lasers, to develop economically feasible conventional lighting products, it may be necessary to combine optical fibers or waveguides to guide and transmit the emitted light.
In the photos and videos of lighting accessories provided by Baja Designs, you can see the semiconductor laser lighting used in off-road vehicles. Baja Designs claims that the lighting distance of their OnX6 Hybrid Laser/LED and XL Laser High Speed Spot spotlights is 350% of that of traditional LED off-road vehicle lighting products, which is very suitable for off-road competitions at night.