With the analysis of advantages and disadvantages of laser lighting using white light illumination and car

Ohio University's FAIZ RAHMAN believes that the phosphor pumped Bai Guangyuan beam, converting from LED to laser can improve the efficiency and prolong the service life and produce highly collimated.

At present, the laser source semi polar laser diode based on GaN, and combined with the advanced technology of fluorescent powder. Because the laser focused on the phosphor on a small point of light and converted into white light, light source can output safe and highly collimated white light. Laser based method, its properties include temperature high than LED. The pump laser is useful, because in the near UV emission devices are easy to obtain, and can effectively play the role of.

From the LED to the process does not occur between the laser night. On the contrary, in the foreseeable future, based on the LED lamp is still the main means of generating white light. However, solid-state lighting system of laser diode has been used in high brightness lighting applications based on, and there are now several manufacturers have produced.

The power of laser diode pumped lamp development is to avoid LED efficiency. However, this is not the only benefit. In addition to the Soraa and several other foreign manufacturers, the use of other LED source chip does not contain short wavelength at about 450nm. Therefore, when the peak wavelength of 450-460nm LED phosphor for cheap pump, the light source will be insufficient in the violet portion of the spectrum.

The white light 405nm ultraviolet light emitting diode laser can avoid this situation. These devices are very cheap and efficient, but also in the market. The use of short wavelength phosphor pumped, spectral output is more abundant, more spectral coverage, and color index is higher than the typical LED pumped Bai Guangyuan (see Figure 1).

Figure 1. from laser diode pumped light light color is almost neutral (x=0.3305, y=0.3309), proved that the spectral richness of light source. The black line is the Planck track.

In many cases, more important than the quality of white is the number. In this way, a laser diode pumped light is very strong, so they are the source of high intensity light architectural lighting, searchlights and automobile headlights ideal. Another attribute of laser source is minimal light beam divergence from the nearly parallel.

The advantages of laser pumping source caused by the automaker's attention, they are actively looking for high-end models of laser headlight installation. Penetration in the automotive industry as LED lighting, high-end models leading the trend, including some of the BMW models (see Figure 2).

Figure 2. BMW laser headlight with laser diode and single beam combiner, phosphor target and reflector assembly.

Laser pumping structure

Unlike LED, when using laser diode pumped phosphors, require different arrangements. Because of its high strength and directional characteristics of laser radiation, can not put the phosphor deposited on top of pump simply. On the contrary, need more optical arrangement, such as the combination of phosphor plate and reflector, or using phosphor coated integrating sphere (see Figure 3).

For these two methods, as long as the use of appropriate technology to combine a plurality of laser beams can be pumped using one or more diode two. This means that the light power of the laser pump module has no upper limit. Another advantage is the use of remote pump structure is not in the hot parts of the phosphor, the phosphor can prevent heating during operation, the service life is prolonged.

A relatively simple method of laser pumped laser radiation is guided to the phosphor plate and reflector alignment obtained (see Figure 3 (a)). However, in the light power conversion, integral ball using phosphor coated more effectively (see Figure 3 (b)).

Figure 3. typical optical laser diode pump set

According to whether you need low power or high power light source, can be used by other programs. For example, a small lamp can be used to pump the beam expanding lens phosphor plate. This method is shown in Figure 4, depicts a single straight light ray tracing simulation.

Figure 4. for small lamp pumped laser is an efficient pump device. The pump light (red light) enter from the left, through the concave lens beam expansion, extended to the right side of the phosphor coating on the glass board, a phosphor layer and incident on the combination of silicone. Under the blue light conversion display. In the figure, fluorescent plate displayed as opaque, separation and green mirror, to can see the light in the trajectory of reflector shell. In the actual lamp, fluorescent plate (allowing light to escape the transparent glass is sealed to the edge of the reflector). The laser module only light reflected back a few back to the left (not shown).

Although the white light laser has many advantages, but also must consider its limitations. Like the LED lights on, the light emitted contains two different components: convert light from the phosphor, and laser remaining unexchanged. However, the use of laser, the biggest difference is that internal consistency, which causes that appear in the bright spots - visible light and dark spots on the surface.

Can not ignore the spot defects, in addition to distraction, it has a negative effect on visual perception, spatial detail obstruct detection illumination. The test showed that the spots will decrease of visual acuity was 40%, lower level of ability to perceive spatial frequency. These problems are a part of direct laser illumination not popular.

Please note that the use of laser projector, by hand