The surface light source uses an organic EL point source as a white light source derived from a semiconductor laser

If the white LEDs are developed like this, is it necessary for a new generation of illumination sources to have white LEDs? ... At present, it is not so simple to draw conclusions. White LEDs are point sources. To get the brightness that can be used for illumination, multiple white LEDs must be juxtaposed to form a single surface. As a point source, the brightness of a white LED is actually not as good as that of a HID lamp. When surface light sources and point light sources are needed, the importance of other light sources other than white LEDs emerges. At the "Green Device Forum 2010", there was a speech that stood at this angle.

From the point of view of the surface light source, Matsushita Electric's 菰田卓哉 introduced the development trend of white organic EL lighting. Putian believes that, like the fluorescent tube and the point source of the white LED as the line source, as a surface light source, the white organic EL will become the unique backbone of the lighting field. Matsushita Electric plans to begin sampling the white organic EL panels in 2011, initially for special lighting, and then for store lighting, which is expected to expand into general lighting after 2014.

Although the luminous efficiency of white organic EL is slightly inferior to that of white LED, it will definitely catch up with white LED in the future. The luminous efficiency of white LED may be basically stabilized at about 200lm/W, and with high efficiency phosphorescence With the continuous development of organic-like EL materials, the gap between white organic EL and white LEDs will rapidly shrink. From the research results of Matsushita Electric Works, it is not a dream to have a product with a luminous efficiency of 130 lm/W around 2014.

As a recent initiative of Matsushita Electric Works, Sakata also introduced the "two-layer multi-unit structure organic EL device". This component is a red, green phosphorescent light-emitting layer (made by U.S. General Display Corporation and Nippon Steel Chemical Co., Ltd.) and blue fluorescent light. The layers (the production system of Idemitsu Kosan) are stacked vertically. The three colors of RGB are uniformly mixed by longitudinal stacking, and even if the angle of viewing the white organic EL panel is changed, the hue of white light is hardly changed. During the speech, the trial panels with color temperatures of 4600K and 3000K (color rendering are all Ra95) were also lit, which emphasized to the audience that the panel could hardly see the angle dependence. In addition, the reason why the fluorescent luminescent material is used in the blue organic EL layer is because there is no practical blue phosphorescent luminescent material at this stage.

Using a semiconductor laser to achieve a brightness of about 2.5 times that of HID

It is Nagahama Shoichi of Nichia Chemical Industry to introduce development measures aimed at the highest end point light source. Nagahama introduced a solid-state light source with a brightness of 270 cd/mm2 and a HID lamp of about 2.5 times. Its brightness is nearly one digit higher than the white LED. The solid-state light source uses a combination of a blue semiconductor laser and a phosphor material for a blue light source of a laser projector. A luminance of 250 lm (current 1.2 A, voltage 4.6 V) was obtained with a diameter of 0.65 mm. It is assumed to be applied to a concentrating light source for image recognition, a special light source for medical and industrial applications, and the like. Called the "white light source that embodies the pursuit of the ultimate light source" (Chang Bin), it also features a simple lens to collect light. During the speech, Nagahama also made a demonstration: using a white light source and an external lens to brighten the venue.

The white light source is constructed by placing the lens on top of the blue semiconductor laser CAN package and wrapping it in other CAN packages. A light-emitting aperture is formed in the center of the outer CAN package to embed the phosphor-doped adhesive therein. The aperture is 0.65 mm. The blue laser is condensed by the lens inside the package and irradiated onto the phosphor, and the phosphor can emit white light to the outside.

Speaking of laser sources, many people think that their life is relatively short. The white light source developed this time has an average brightness reduction of 20,000 hours at a case temperature of 25 ° C. The lifetime of the laser is determined by the degradation of the reflective layer within the package and the decrease in reflectivity. Since the blue semiconductor laser has a lifetime of 40,000 hours at a case temperature of 50 ° C, it is expected that the brightness reduction life can be extended to more than 30,000 hours if the reflective layer is improved. The lens of the white light source and the lens inside the package and the binder mixed with the phosphor material are both inorganic materials. This is because a strong blue laser is used, and if a resin material is used, it is quickly deteriorated. In addition, although the laser light source gives an impression that it is more expensive than the LED, it uses a laser for a projector, and can also be manufactured by a semiconductor mass production technique using a blue-violet semiconductor laser element such as a Blu-ray recorder, so that only a laser element is required. When mass production begins, there will be potential to lower prices.

Although the light source is extremely bright, the luminous efficiency is only 45 lm/W. Compared with the white LED with luminous efficiency above 100 lm/W, it is slightly inferior. According to Chang Bin, so far, at the expense of efficiency to pursue high brightness, I really want to improve the luminous efficiency, there is still a way. The phosphor embedded portion has a diameter of 0.65 mm, and there are some light inside the package that is not exposed to the outside. If the brightness is not required to achieve a HID of 2.5 times, some means can be taken to enlarge the diameter of the phosphor embedded portion. The light thus wasted can be radiated to the outside of the package, thereby improving luminous efficiency.