FAIZ RAHMAN from the University of Ohio in the United States suggests that replacing LEDs with lasers in phosphor-pumped white light sources can significantly enhance efficiency, extend service life, and produce highly directional beams. Today’s laser-based systems utilize semi-polar GaN laser diodes paired with advanced phosphor technology. These systems concentrate laser energy on a small spot of phosphor, converting it into white light efficiently and safely. Compared to LEDs, laser pumping generates much less heat, making it more reliable and durable. Additionally, near-ultraviolet laser diodes are readily available and effective for this purpose.
Although the transition from LED to laser is not immediate, LED-based lighting will continue to dominate for the foreseeable future. However, laser-based solid-state lighting has already found its place in high-brightness applications and is now offered by several manufacturers. One key driver behind this shift is to avoid the efficiency drop seen in LEDs. Another advantage is that many LED chips do not emit wavelengths below 450 nm, which limits the color spectrum when used for phosphor pumping. This issue can be resolved by using a 405 nm UV laser, which is cost-effective, efficient, and widely available. It offers a richer spectral output, broader coverage, and a higher color rendering index than traditional LED-pumped white light.
In some applications, the intensity of light is more important than its quality. Laser-pumped light is ideal for architectural lighting, searchlights, and car headlights due to its high brightness and nearly parallel beam. Automakers have taken notice, with luxury models like BMW incorporating laser headlights. Just as LEDs revolutionized automotive lighting, high-end models are leading the way in adopting laser technology.
Laser-pumped lighting requires different optical setups compared to LEDs. Due to the focused nature of laser radiation, phosphors cannot be simply placed on top of the laser source. Instead, configurations such as phosphor plates with reflectors or phosphor-coated integrating spheres are used. These setups allow for multiple laser beams to be combined, enabling high optical power without limits. Remote pumping also helps protect the phosphor from heat, extending its lifespan.
A simple method involves directing the laser at a phosphor plate and collimating the light with a reflector. However, using a phosphor-coated integrating sphere is more efficient in terms of optical conversion. For smaller systems, a beam expander lens can be used to evenly distribute the laser across the phosphor surface. Simulations show that this setup optimizes light conversion and minimizes losses.
Despite its advantages, laser-pumped lighting has some drawbacks. The coherent nature of lasers can create visible speckle patterns, which can be distracting and affect visual clarity. However, these issues are minimized when the laser interacts with the phosphor layer. The resulting light is rich in color and free from spots, offering better performance than LED lighting.
The main disadvantage of laser-pumped systems is their cost. Laser diodes are significantly more expensive than LEDs, limiting their use to specialized applications. Additionally, laser diodes have a shorter lifespan, especially under high-power operation. This is due to crystal defects that worsen over time, reducing light output. However, advancements in native GaN substrates are helping to reduce these issues.
As laser technology matures, costs are expected to decrease through economies of scale. This could open new markets for UV and near-UV laser diodes. While LEDs remain dominant today, laser-based lighting is gaining momentum and may soon become a major player in the industry.
Source: LED Network
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