Master the balance between luminous efficiency

Master the balance between luminous efficiency

In addition to improving luminous efficiency, there are roughly five projects that LED manufacturers are accelerating to develop. Namely: "cost competitiveness" of white LED, "temperature stability" without degrading performance at high temperature, high "color rendering index" for illumination, hue "uniformity" between white LED products, output per unit package "The size of the luminous flux" (Figure 4). All of these projects and the luminous efficiency belong to this trade-off relationship. To balance the luminous efficiency, it needs to be handled carefully.

Figure 4: It won't be a bestseller with high efficiency alone
In order to meet the market requirements, LED manufacturers need to pursue cost competitiveness, temperature stability, color rendering index, uniformity of light, and luminous flux per unit of white LED in addition to the technical strength of achieving luminous efficiency of 200 lm/W or more.

The key to "cost competitiveness" is to reduce the manufacturing cost of blue LED chips that account for about 60% of the cost of white LEDs (Figure 5). The conventional method is to expand the production line. However, this alone does not solve the problem. The method proposed by Japanese and American old LED manufacturers, which is one step ahead in the development of white LEDs, is to reduce the size of blue LED chips. That is to increase the number of chips that can be made on one wafer.

Figure 5: Cost structure of white LEDs Among the various costs of white LEDs, LED chips account for more than half of the total, at 62%. (Figure: DisplaySearch)

In large-size LCD panel backlights where the unit price of brightness is 20 to 30% lower than that of lighting, and there is a fierce price competition, there are significant differences in chip size among different LED manufacturers (Fig. 6). Compared with Korean manufacturers' products, Nichia's chip size is only about 1/3 to 1/2 of that of Korean manufacturers. The miniaturization of chips may also affect the use of lighting that is constantly intensifying in the future.

Figure 6: Large difference in size of LED chips. A survey of white LEDs with the same input power of each company revealed that the size of the used blue LED chips varied greatly. For example, compared with Korean manufacturers' products, Nichia's 0.1W products are only about 1/3 of them, and 0.5W products are only about 1/2. (The map is produced by the site based on the information of DisplaySearch)