Research on Temperature Characteristics of White Light Illuminated LED Lamps by Jin Shangzhong Zhang Shusheng Institute of Optoelectronic Technology, China Institute of Metrology (310034) Hou Minxian The Optoelectronic Information Department of Zhejiang University (310027) caused long shift of blue peaks and increased with increasing current;
The color coordinates, color temperature and color rendering index did not cause a large change, and the luminous efficiency decreased. The main reason is that the long shift of the blue peak causes a mismatch between the phosphor and the excitation wavelength, causing a decrease in the luminous efficiency of the phosphor. This phenomenon has also been confirmed by illumination at different ambient temperatures…
Using blue LED as the basic light source, a part of the blue light emitted by the blue LED is used to excite the phosphor, so that the phosphor emits yellow or red light and green light, and the other part of the blue light is transmitted, and the yellow or green light of the phosphor is The green light and the transmitted blue light constitute white light, as shown in (L).
At this time, there are two requirements for the phosphor: one is that the excitation wavelength of the phosphor matches the emission wavelength of the light-emitting diode to ensure high conversion efficiency, and the second is that the emission of the phosphor and the illumination of the blue LED can be matched. White light. White light can be easily achieved by simply selecting the phosphor and then adjusting the ratio of phosphor to blue light.
As an illumination source, its light color parameters are: total luminous flux! , chromaticity coordinates x, y, u, V, color temperature! C, color rendering index a, luminous efficiency”. In order to analyze the influence of driving current and temperature on LED color parameters, we have established an LED test device as shown, the LED is placed in a 180mm diameter integrating sphere, and the integrating sphere is placed. In the incubator, the light from the LED is transmitted through the optical cable to the SSP3112 LED spectral analysis system for measurement.
In order to drive the square wave constant current source of the LED, the current is adjustable from 1 to 1000 mA, the frequency is 1 kHz, and the duty ratio is 1/8. 3 Experimental Results and Analysis The light color characteristics of the white LED light source are affected by the chip and the phosphor, The effects of drive current and ambient temperature, Table 1 shows the light color parameters of the phosphor white LED under different operating currents, where is the working current of the white LED; ‘, (for its chromaticity coordinates; a, !c and Color rendering index, correlated color temperature, and peak wavelength.
Table 1 shows the light color parameters of the fluorescent white LED under different working currents. The color rendering index of the fluorescent white LED is about 80. As the working current increases, the blue peak wavelength shifts slightly longer, and the color rendering index increases slightly.
However, it is not obvious; when the operating current reaches 560 mA, the color rendering index is only 83. Therefore, it is not appropriate to increase the color rendering index by increasing the operating current of the white LED.
In fact, from the relative spectral power distribution of its luminescence to P(!)((C)), it can be seen that its long-wave part is much smaller than sunlight, and we supplement the white LED lamp with a red LED with a wavelength of 650 nm. The spectrum of the white LED operating current is 25mA and the red LED operating current is 10mA. The color rendering index of the combined LED can reach 93. It is the best way to increase the red light energy of the phosphor.
For the white light of the combination of red, green and blue LEDs, the working current of red, green and blue can be adjusted to obtain a certain color rendering index, even reaching 90. However, the current regulation is complicated and the consistency is poor. .
Therefore, as the LED light source for illumination, phosphor white LEDs should be used. Table 2 shows the relationship between white LED luminous efficiency and working current. Table 3 shows the combination of red, green and blue LEDs. Variety. It can be seen that the luminous efficiency of the phosphor white LED is higher than that of the three primary color combined white LED light source.
Table 2 The relationship between white LED luminous efficiency and working current Table 3 Red 7 green 7 blue LED luminous efficiency and current relationship Table 4 gives the combination of white LED and red LED; see Table 2, Table 4, white LED The luminous efficiency decreases as the current increases, because the increase in current causes a long shift in the blue peak, which reduces the efficiency of matching the phosphor to the excitation wavelength.
Therefore, reducing the operating current of the LED can increase its luminous efficiency, but the number of LEDs required to achieve the same luminous flux increases, and the cost increases. As the power increases, the luminous flux also increases, but there is a maximum value, and the corresponding current is about 20 mA. From the saving of the number of LEDs, the current of the constant current driving LED lamp can be selected (40 ~ 50) mA.
7 Red LED luminous efficiency and current relationship In summary, we chose 100 white LEDs and 20 red LEDs to form an illumination source, each LED current is 40mA, measured its total luminous flux is 307lm, luminous efficiency is 19.88lm / W, the color rendering index is 91.
The LED lamp is placed in an incubator for measurement. The results are shown in Table 5. It can be seen that the temperature rises and the luminous efficiency decreases. When the temperature is greater than 50:, the color temperature is high and the color rendering index is deteriorated. Mainly due to the increase in temperature, the blue wave peak shifts and the peak of the phosphor becomes flat and deteriorates.
Table 5 The influence of temperature on the parameters of LED lamps 4 Conclusion As a white LED light source for illumination, phosphor-type LEDs should be used. The color characteristics of the LEDs are affected by the driving current and the ambient temperature, in addition to the influence of the chip and the phosphor.
The driving current of the LED is preferably about 20 mA, and the light has a good luminous efficiency when the temperature is less than 50:. The color rendering index is improved by adding a red component.
In order to achieve practical use, it is not mature to change the use condition of LED white light illumination source to improve the light color performance; relying on the improvement of technology, the development of materials and device technology level can improve the light color characteristics of white LED.
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