[Special Feature] Interpretation of the 2013 China Association for Science and Technology National Development Report (1)

First, the application of LED

The characteristics of the LED determine that in addition to its visual use, there are many other applications, namely non-visual applications. What is currently known mainly includes agriculture, medical and other fields. If the application of light in these fields is called the generalized lighting discipline, the connotation of the lighting discipline will be greatly developed.

1. LED application in agriculture

The application of LED in agriculture is mainly used for the supplementation of plants, while the growth of plants depends on the photosynthesis of sunlight. Biological statistics show that most of the plants are green plants, which contain chlorophyll a and chlorophyll b, while chlorophyll a and chlorophyll b selectively absorb the spectrum. Plants containing chlorophyll a and chlorophyll b have little absorption of green light, and their main absorption peaks are around 650 nm and 440 nm, respectively, and chlorophyll a and chlorophyll b absorption peaks are different but relatively close. Therefore, it can be considered that the growth of plants mainly relies on these spectra for photosynthesis. Further research has also shown that the absorption of different wavelengths of light by different plants is not the same as that of photosynthesis. This is also understood from the fact that different plants have different colors (ie, reflecting sunlight).

Due to the large spectral flexibility of LEDs, we can choose the right spectrum for different plants to illuminate. It is conceivable that such plant fill light will have a greater efficiency advantage than traditional light sources. In this LED application, establishing a spectral photosynthesis efficiency curve for different plants is the basis for improving efficiency. Therefore, with the current visual science, will plant science of photosynthesis be produced?

The application of LED in agriculture also includes insecticide, antibacterial and so on. If some specific spectra have inhibitory effects on certain insects and fungi, it is of great significance to study this inhibition, and this will give birth to another type of lighting scientific research.

In addition, LEDs are also very useful in animal farming. Its main application is to create a preferred illumination light environment for animals, which is also a subject for illumination science to be studied.

2, LED application in medical

The application of LED in medical treatment mainly includes light therapy and rehabilitation, and health care.

The principle of light therapy is that monochromatic light of a specific wavelength has the ability to affect the biological behavior of cells without obvious damage. For a long time, lasers have been used as illumination sources because of their large size, high price, and inability to illuminate large areas of wounds.

Compared with lasers, LED light sources are small in size, relatively inexpensive, and have various spectra. Multiple LEDs can be arrayed for large-area wound irradiation, and wavelengths of light therapy can be optimized by selecting LEDs of different wavelengths. Coupled with the high efficiency of LED, LED has great potential in light therapy. The application of LED in health care and rehabilitation is based on the same principle.

In these LED medical applications, there is also a preferred problem of LED illumination, which is the most suitable spectrum for a certain treatment, what kind of intensity, what kind of illumination method (pulse mode / steady state mode) is most suitable? How best? These are the broad categories of lighting disciplines that are worthy of scientific research.

The application of LED in medical treatment is slightly different from that of agriculture. In medical applications, because of the various tissues in the human body, the LED light source should not only consider the promotion of the growth of certain tissues, but also the damage of other various tissues. Therefore, the research of LED in medicine will be more complicated.

With the development of LED technology, in addition to the above, LED will also be born with various applications, and the research of these applications will greatly enrich the research connotation of the lighting discipline.

It is worth mentioning that the LED visible light communication technology generated by the combination of LED and communication technology will have great application prospects. However, in LED communication, the LED is just a carrier. Therefore, although this is an interdisciplinary subject related to lighting in the future, strictly speaking, this is not part of the lighting discipline, but part of the communication discipline.

Second, LED changes the focus of lighting disciplines

The lighting discipline is based on photometry and colorimetry, in which photometry was founded by scientist Lambert in 1760, while colorimetry has undergone a relatively long process, from CIE1931, CIE1964, CIE1976. The correction of the CIE chromaticity system was completed; in 1974, the evaluation index of color rendering was basically determined. In the nearly four decades since then, there has been no major development in the lighting discipline itself. The reason is that the light source as the material basis of illumination, including the heat radiation source and the gas discharge source, has no major changes in the basic forms such as the spectrum, and the illumination discipline based on photometry and colorimetry can basically satisfy the adoption. The lighting practice of these sources is required.

In the 1980s, foreign manufacturers first invented compact fluorescent lamps. After nearly ten years, all countries have devoted themselves to the study of light efficiency, color rendering and lifespan, and made great progress, so that CFL has become the most important source of indoor lighting. As the HID light source in the 1960s, it has always been a hot spot in light source research, and in this regard, in terms of light efficiency, color rendering, and lifetime of lamps, this field has created another important international conference and organization in the field of lighting, namely LS: XX Conference and FAST-LS, and make LS Conference the most important international conference in the field of lighting except CIE.

The focus of the lighting discipline has always been to be the light source of the material basis of illumination, not the illumination itself, and the emergence of LEDs will change this situation.

In recent years, LED technology has developed rapidly. One of the most important indicators - light efficiency has been increased from 10 lm / W a decade ago to 130 lm / W of the current commercial products, and the laboratory sample has reached 300 lm / W. Above, and the price is very close to the people. At the same time, due to the great improvement of the life and reliability of LED devices, the infinite flexibility of LED in scale space, spectral space and time space is highlighting the advantages. At present, LED has become the mainstream light source in the fields of signal and display; in the field of visual lighting (indoor, outdoor, etc.), it has occupied a leading position; in the fields of agriculture, medical care, communication, etc., it has also grown rapidly in recent years.

In the above LED application prospects, all are based on three infinite flexibility of LED. However, the current development of LEDs has not fully realized this flexibility of LEDs, especially the infinite flexibility of LED spectrum. In general, the spectral half-width of an LED is 20-30 nm, and most of the spectrum in the visible range can be realized by changing the doping of the LED material, since the achievable LED photoelectric efficiency of each central wavelength is different, especially the green LED. The efficiency is very low, and the current commercial products are still below 20%. Therefore, increasing the photoelectric efficiency of green LEDs will be a necessary condition for realizing the infinite flexibility of the true spectrum of LEDs. Before the efficiency of LED green light has not been greatly developed, research on improving the photoelectric efficiency of green LEDs will be a research focus of the lighting discipline.