FAIZ RAHMAN from the University of Ohio in the United States suggests that replacing LEDs with lasers in phosphor-pumped white light sources could significantly improve efficiency, extend lifespan, and produce highly directional beams. Currently, laser-based systems use semi-polar GaN laser diodes combined with advanced phosphor technology. These lasers focus on a small area of the phosphor to generate white light, resulting in a safe and collimated output. Compared to LEDs, laser pumping generates less heat, making it more energy-efficient. Additionally, near-ultraviolet (UV) laser diodes are widely available and effective for this purpose.
While transitioning from LEDs to lasers is not immediate, LED-based lighting will continue to dominate in the near future. However, laser-based solid-state lighting has already found practical use in high-brightness applications and is now offered by several manufacturers. One major driver behind this shift is the desire to avoid the efficiency loss seen in LEDs over time. Another benefit is that many LED chips do not emit wavelengths shorter than 450 nm, which can lead to an insufficient purple component when used for phosphor pumping. Using a 405 nm UV laser instead ensures a richer spectrum, better color rendering, and a more natural white light, as shown in Figure 1.
In many applications, brightness matters more than color quality. Laser diodes excel in high-intensity lighting, such as architectural lighting, searchlights, and car headlights. Their light beams are highly collimated and nearly parallel, making them ideal for long-range illumination. Automakers have started incorporating laser headlights into premium models, similar to how LEDs revolutionized automotive lighting. BMW, for example, has integrated laser headlamps in some of its high-end vehicles, as illustrated in Figure 2.
Laser-pumped lighting requires different optical setups compared to LEDs. Due to the intense and directional nature of laser light, simply placing phosphor on top of the source isn’t sufficient. Instead, structures like phosphor plates with reflectors or phosphor-coated integrating spheres are used to distribute the light evenly. This remote pumping method also helps protect the phosphor from heat, extending its lifespan. A simple setup involves directing the laser at a phosphor plate and using a reflector to collimate the output. For higher efficiency, a phosphor-coated integrating sphere is preferred.
For smaller luminaires, a beam expander lens can be used to spread the laser across the entire phosphor plate, as demonstrated in Figure 4. The simulation shows how the laser expands, hits the phosphor, and converts into visible light. Although laser-pumped white light offers numerous advantages, it also presents challenges. One issue is speckle—visible spots caused by the coherent nature of laser light. These spots can reduce visual clarity and make it harder to perceive fine details. However, in phosphor-pumped systems, the spots are much smaller due to multiple scattering within the phosphor layer, making them less noticeable.
Despite these benefits, laser-pumped lighting still faces obstacles. The primary drawback is cost. Laser diodes are significantly more expensive than LEDs, limiting their use to specialized applications. While they offer a wide range of power outputs, combining multiple lasers can shorten system lifespan due to increased stress on the diodes. Over time, crystal defects can develop, reducing performance. However, improvements in GaN substrates are helping to mitigate these issues.
As laser technology matures, costs are expected to drop, opening new markets for UV and near-UV laser diodes. While LEDs currently lead the market, laser-based lighting is gaining traction and may soon become more widespread. For more information, visit LEDinside’s official website or follow their WeChat public account.
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