LED light up everything: achieve 200lmW above luminous efficiency and ease of use

To achieve the luminous efficiency of white LED is above 200lm/W, continuous improvement. However, the white LED must have the characteristics of the light-emitting efficiency is not only. In the process of popularization of white LED, temperature stability and color rendering index can be opened up more and more factors.

Luminous efficiency is steadily increasing at an average annual rate of 15%, will soon reach 200lm/W...... White LED luminous efficiency will continue until when, and to what extent?

In fact, the luminous efficiency of the research and development level is almost the limit (Figure 1). The idea that the combination can be used to get the highest luminous efficiency of blue LED and yellow fluorescent material, such as white LED, the limit is around 260lm/W. The current level of research and development has been more than 200lm/W, little room for growth. "There is no doubt that the speed of technological innovation will be more and more slow" (OSRAM Japan). Many stakeholders believe that before 2020, the luminous efficiency of white LED will reach a peak. However, a few years later, the luminous efficiency of white LED products is still an indispensable indicator of the strength of LED manufacturers. Because the luminous efficiency of existing products and the limit value, there are nearly two times the gap.

Figure 1: the limit of the luminous efficiency of the limit white LED is believed to be around 260lm/W.

It should be noted that, while the use of white LED continues to expand at the same time, luminous efficiency supremacy of the situation is gradually collapse. The level of luminous efficiency reflects the level of energy efficiency, but also to reduce the unit price per unit brightness (yen /lm) an important indicator. However, in the white LED is widely used for a variety of purposes today, simply by the luminous efficiency has been unable to determine whether to meet the requirements of white LED manufacturers, such as product vendors. In the future, this trend will be further enhanced.

In this case, LED manufacturers in the development of the technology can achieve more than 200lm/W luminous efficiency, but also to accelerate the development of other characteristics of white LED. Here's a look at the latest trends in the development of white LED.

Internal quantum efficiency is improved

There are a lot of LED vendors who think there is room for improvement in blue chip LED and fluorescent materials (Figure 2 (a)).

Figure 2: to achieve more than 200lm/W luminous efficiency focus

In the future, in order to improve the luminous efficiency above 200lm/W, we must improve the internal quantum efficiency and the wavelength conversion efficiency of the phosphor in the blue LED chip. (Figure) (b) produced by PHILPS at this site

The input to the power conversion of white LED light output to the outside of the process are as follows: LED to the blue chip input power, a blue light; the fluorescent material will be part of the blue light wavelength conversion for long wavelength of visible light; the blue light and a hybrid optical wavelength conversion into white light output to the external package. In order to improve the luminous efficiency, it is necessary to reduce the energy loss in each link.

Each link requires the following technology: to reduce the resistance loss, the internal quantum efficiency, improve the electron photon emitting layer will improve the photon output to the blue LED chip to improve the light extraction efficiency; wavelength conversion efficiency; improving the output white light to package the light extraction efficiency, etc.. So far, manufacturers have proposed a variety of improvement measures, and achieved remarkable results.

For example, the index of resistance loss - the forward voltage of white LED is significantly lower than the original. Lighting products commonly used in 1W products, the forward voltage is close to 4V, and now has been reduced to 2.9 ~ 3V (Figure 3). From the blue light energy (2.75eV) point of view, before the input power of 20 to more than 30% due to the loss of resistance, and now only about the loss of about 5%. Light extraction efficiency is also greatly improved, of which the highest product is about 70%, at the level of R & D reached 90%.

Figure 3: the forward voltage is at the lower limit

The input power supply for lighting purposes Nichia 1W white LED, the forward voltage decreased sharply in recent years. In 2011, the new product was 3V, which was close to the lower limit of forward voltage (2.75V). The difference between the lower limit and the forward voltage will cause the loss of energy. In order to achieve the luminous efficiency above 200lm/W, the internal quantum efficiency and the wavelength conversion efficiency of the system should be improved on the basis of all the above improvements. Because the space between the two is relatively large. For example, the internal quantum efficiency is currently 50 to 70% level. The United States PHILPS (Philips Lumileds Lighting) announced the LM, will make every LED 1000lm chip with high output and high efficiency white LED, the internal quantum efficiency needs to be improved to more than 80% (Figure 2 (b)).

There is room for improvement in crystalline quality and luminescent layer structure

How will the internal quantum efficiency and wavelength conversion efficiency be improved? The internal quantum efficiency, need to improve the luminescence layer material -- GaN semiconductor epitaxial crystal crystal quality and light emitting layer structure; on wavelength conversion efficiency needs to be improved, the development of new materials and fluorescence materials. These initiatives have been carried out since the launch of the white LED.

In addition, the invention also provides a method for improving the internal quantum efficiency by changing the crystal surface of the GaN system from the current polar surface to the non-polar surface. The method has been in the research and development stage, but has recently begun to move towards practical stage. For example, South Korea