The concept of ‘full spectrum’ LEDs

The real ‘full spectrum’ refers to the light emitted by the light source contains from the ultraviolet - visible - infrared range of all wavelengths of the spectral curve, that is, the sun emitted by the complete spectrum (such as the spectral curve shown in Figure 1), which is also the most comprehensive nature ‘full spectrum This is also the most comprehensive ‘full spectrum’ in nature. The most talked about LED ‘full spectrum’ refers to a narrower point of the ‘full spectrum’, LED ‘full spectrum’ refers to the light emitted by the LED light source in the visible range of light. Close to the sun in the visible range of light emitted by the spectral curve (shown in Figure 2). Removed the ultraviolet and infrared light two parts, the main reason for removing these two parts is to make the full spectrum of the LED has the possibility of industrialization, so that the full spectrum of the LED to do ‘simpler’. If you want to add ultraviolet and infrared light to do the real full spectrum, basically there is no mass production and the possibility of practical application, because the whole packaging system and subsequent application will become very complex and exceptionally difficult. Even if the removal of ultraviolet and infrared light full spectrum, do a relatively ‘simple’ in practice is not so simple, such as to do full spectrum of the finger must be very close to 100, and many companies want to do from 96 to 98% of the finger feel very difficult, not to mention the finger to 99 or even more than 99.

Figure 1 Complete spectral curve of sunlight (280 nm-4000 nm)

Figure 2 Spectral curve of sunlight in the visible range (380 nm-780 nm)

Full-spectrum LED implementation

LED to achieve the full spectrum of the way can be derived from the theoretical analysis, is nothing more than from the chip and phosphor two major directions to do. Chip is mainly two ways, one is the chip excitation phosphor, the other is only using the chip without phosphor. The phosphor must be used in conjunction with the chip, different emission wavelengths and excitation wavelengths to match the combination. Comprehensive view of the full-spectrum LED to achieve four main ways a single-band blue chip phosphor excitation; two is a dual-band blue chip/three band blue chip phosphor excitation; three is a violet chip phosphor excitation; four is a combination of multiple chips. The following is a detailed description of each of these four ways.

First, the way of single-band blue light chip excitation phosphor. This way is basically the same as the ordinary LED package, the difference is that to make the spectral curve issued by the LED is close to the full spectrum, a variety of phosphors will be added, such as green powder, yellow powder, red powder, and even add orange powder, green powder, blue powder and so on. Although this approach can also be made close to the full spectrum of the effect, but there will still be a relatively strong blue light peaks, in addition, due to the lime green powder and blue powder blue light excitation efficiency is very low and the existence of re-absorption between the phosphor problem, the spectral curve issued by the missing 470-510nm range of light will still.

Second, the way of double-band blue light chip/triple-band blue light chip excitation phosphor. The effect of this way will be greatly improved relative to the way of single-band blue light chip. By matching the high and low blue light wavelengths of dual-band blue light chip and using a variety of phosphors, it can make up for the missing light in the range of 470-510nm. Dual-band blue light chips usually choose two wavelength ranges of430-450nm and 460-480nm, together with the use of 490-510nm cyan-green powder, 510-550nm green powder, 550-580nmyellow powder, 580-600nm orange powder, and 630-660nm deep red phosphor. Tri-band Blu-ray chips usually choose a combination of chips in the wavelength ranges of 430440nm, 440-460nm and 460-480nm, and the phosphor scheme is like the dual-band Blu-ray chip scheme. This approach can be flexibly adjusted through the wavelength band of the chip and phosphor band and ratio to achieve closer to the solar spectrum (as shown in Figure 3), the apparent index can be achieved more than98. However, this solution requires the addition of many types of phosphors, different wavelengths of the phosphor system may also be different, which will be more demanding on the phosphor proportioning personnel, the stability of the proportion of mass production process and batch consistency will be more difficult to control. Currently there are some phosphor manufacturers will be two or more than two kinds of phosphor pre-mixed, and then given to the encapsulation plant to use, this way will greatly reduce the difficulty of the encapsulation plant powder, but note that the pre-mixed phosphor in the transport and storage process may be separated from the settling of phosphor resulting in poor mixing effect of the problem, The main reason for the problem of sedimentation separation is that phosphor manufacturers produce two different phosphors and then mixed together, and when there are differences in the particle size and particle size distribution of the two phosphors, there will be a large particle size of the phosphor settlement phenomenon.

Figure 3-1 Full spectrum curves of Dual-band blue light.  (for reference

only)

Figure 3-2 Full spectrum curves of Triple-band blue light (for reference

only)

Third, the way of violet chip excitation phosphor. This way of light efficiency is relatively low, the main reason is that the phosphor on the market is basically matched to the blue chip to research and development, the highest efficiency of the mature phosphor excitation point is usually in the blue light band range, although the range of violet light there is also an excitation peak, but the excitation efficiency will be much lower. In addition, the wavelength of the violet chip is usually in the range of 385-405nm, the chip itself is not high efficiency, resulting in the overall light efficiency will be relatively low, and the cost of violet chips will be higher than the blue chip. But the spectrum from violet chip solution can maximize the proximity of the solar spectrum, out of the spectrum of high saturation, while also avoiding the emergence of short-wave blue light (as shown in Figure 4). Violet full-spectrum products need to pay attention to one point is the product in the long-term aging and use process, the phosphor by the long-term radiation and excitation of violet light attenuation will be greater, compared with the blue-chip scheme is more likely to appear later color drift and color temperature anomalies. In addition, violet light on the package glue and stent plastic material and other organic materials used in the package damage will be greater, which will lead to shorten the life of the LED. In addition, violet LED in a long time after use, there may be violet light leakage problems, this point also needs special attention.

Figure 4 Full-spectrum curve of violet chip (for reference only)

Fourth, the way of multiple chip combinations. This approach can use a combination of blue, cyan, green, yellow,and red chips to achieve full spectrum. in principle, this approach is also suitable to achieve the full spectrum of white light, but why fewer people use this approach to do the full spectrum? May be affected by the following aspects, first of all, the light emitted by the chip is usually a narrower half-wave width, it is difficult to achieve a similar phosphor such a wide half-wave width to the spectrum of the material issued by the effect, Secondly, the electro-optical conversion efficiency of different light-emitting color chips varies greatly, the electro-optical conversion efficiency of blue light chips is usually higher, while other types of chips have lower electro-optical conversion efficiency so that it is difficult to adjust to the same package in the state of light-color balance. Again, different light-emitting color chip aging and use of the process of attenuation differences, blue chip attenuation is slow, yellow and red chip attenuation fast, so that the long-term aging and use of the process of color fluttering and color temperature anomalies, it is difficult to achieve a good use of the results. In addition, the multi-chip combination can also add phosphor to achieve the full spectrum, with the chip to stimulate the phosphor is closer to the way. Usually, this multi-chip and then add phosphor powder will be more difficult to match the powder, because the spectrum and color point changes will be affected by other light-emitting color chips in the package.

The application of full-spectrum LEDs

Above ways to achieve the full spectrum of LEDs, that should be how to apply the full-spectrum LEDs well? This is another very important issue. In the description of the full spectrum of the application of the first point we must first figure out is that in the application of the LED light source in the process there is another parameter that must be considered - the color temperature. 

And sunlight at different times of the day or in different seasons are different, such as sunrise in the morning when the sun's color temperature in 2000K or so, at noon when it is 5000K or so, when the sunset is 2300K or so. So full-spectrum LED also need to consider the different color temperatures based on achieving close to the corresponding color temperature under the effect of the sun's full-spectrum, of course, different color temperatures of the full-spectrum can also be achieved through the above several ways. This gives rise to a series of full-spectrum LED technology solutions. Based on the above description we can know, full spectrum LED light source can be used in almost any conventional lamps and lanterns, such as our conventional lighting household lamps and lanterns, outdoor lamps and lanterns, industrial lighting fixtures, table lamps, plant lighting and so on. Specific applications depend more on the price and acceptance of people. Currently the most applications should be desk lamps, the main propaganda is low blue light, eye protection, color temperature adjustable, etc., this kind of desk lamps will be higher than the ordinary desk lamp premium. 

Based on the above introduction of full-spectrum LED technology, we need to consider: the current ‘full-spectrum’ is a good light source that people really need?