Methods the influence factors, the efficiency of the LED adjustment efficiency and reduce the cost of system analysis

Because LED has a variety of advantages, has become an important part of the semiconductor light source for general lighting applications. For a long time, the efficiency of LED was significantly higher than that of traditional lighting technology. But how to define the solid-state lighting (SSL) system efficiency? In ordinary language, talked about the efficiency of light, we usually refer to the luminous efficiency of them, in lumens per watt (lm/W) unit. Another measure is the radiation power. The need to consider the influence of the effectiveness and efficiency of the decision-making process, discuss product development personnel must follow, because this will affect the efficiency of the whole system.

The calculation function includes determining the light source (LM) measurement of the luminous flux and the electric power input (W). On the contrary, the amount of radiation is not considered corresponding photometric sensitivity of human eyes, but a pure efficiency measurement. The electric power input (W) divided by the light emission output power (W) that the percentage of efficiency. The efficiency of LED depends on many different factors. In this paper we will introduce some of them.

Color temperature affect the efficiency of LED

The choice of color temperature has an important influence on the lighting efficiency, a method can be used for efficient plan lighting solutions in the framework of the existing provisions in lighting. High temperature LED (such as 5000K) is usually higher than the low temperature (e.g. 3000K) higher efficiency. Curve in Figure 1 shows the LED in color index (CRI) spectra of different CCT value Ra> 80 (or SPD - spectral power distribution). SPD curve based on the sensitivity curve of V.

Figure 1. depicts the distribution curve of 80-CRI LED power spectrum at different CCT values.

In order for LED to produce white light, usually using LED chip emitting blue light. Some of these lights light into the longer wavelength converter or by phosphor (green, yellow and red light) light, all these colors together and produce white light. But the conversion process will be a loss, change the wavelength of the light increases, the greater the loss, the reason is the higher level (blue light) and relatively low level light (red light) the difference between the energy is converted into heat. To minimize the loss to need the accurate calculation of the absorption and emission wavelength converter.

However, the simplified condition is sufficient to explain the basic principles. For example, for the warm temperature of 3000K, need to convert large red light. However, this requirement leads to greater losses, compared with 4000K, reduce the luminous efficiency. For the high temperature 5000K, Blu Ray only converted into green, don't need to be converted to red light, which is why the ratio to increase the luminous efficiency of 4000K. Efficiency comparison as shown in figure 2.

Figure 2. depicts the curves of different CCT in CRI Ra 80 the relative luminous efficiency.

Effects of color on efficiency of LED

As mentioned above, select the appropriate converter, after conversion, has a decisive influence on the composition of LED chromatographic efficiency. The converter designed for different combination of CRI and development, particularly optimized for CRI and efficiency. Show the red line, CRI 70, 80 and 90 of the difference between can see very clearly. In order to truly reproduce the color, a very high proportion to long wave; in other words, the red light in the end.

Figure 3 4000K LED at different CRI values SPD. A high proportion of red CRI 90 version can be seen clearly. As mentioned above, to produce such a high proportion will involve high loss. In addition, most of the red energy produced significantly beyond the sensitivity curve of human V lambda, which leads to further reduce the luminous efficiency. Different color temperature luminous efficiency of LED in range 5%, under the influence of different values of CRI are usually in the range 15% in (Figure 4).

Figure 3. depicts the 4000K-CCT curve of LED in different CRI value SPD.

Figure 4. depicts the different color value in the 4000K (CRI Ra) the relative luminous efficiency.

However, the special requirements of LED temperature and CRI will be standardized, standard and application specific constraints. The conventional lighting technology can also see a similar effect.

The efficiency of LED adjustable

Compared with the conventional light source, LED photoelectric semiconductor provides another dimension, lamp manufacturers can adjust and set the efficiency or luminous efficiency based on application specific, i.e. current density.

LED usually grouped according to the brightness and color of a working current. For a group of conditions, so it can be suitable for application and is expected to reach the level of efficiency of light emitting efficiency by changing the current density.

For example, if the luminous efficiency of 130 lm/W LED in the specified current packet, the current work can be reduced to 40%, eventually improve the luminous efficiency of 20% to 156 lm/W. if the working current is increased to 140%, the luminous efficiency will be reduced by 10% to 117 lm/W. Table 1 summarizes the current situation of variable density.

With the corresponding impact table 1. changes of current density.

Table 2. based on two different LED theory, product developers face a trade-off in LED system design.

The efficiency curve also depends on other parameters, such as temperature or the maximum working conditions meet the need. On these two points, the absolute flux LED will naturally change. We will see the results carefully in the next section.

More efficient use of LED to reduce the cost of the system

In the process of development, LED becomes more bright, so the efficiency is more and more high. However, some applications do not necessarily need to be more efficient. So, why is there such a big demand for more bright LED? There is no doubt that one of the reasons is more efficient LED can significantly reduce the cost in solid state lighting system level.

Look at an example. In order to carry out the following comparison