0 Preface
Many people have experience of being inferior in the afternoon, especially after eating lunch. When the degree of lethargy increases, the work efficiency is reduced. In addition to a nap or a cup of aromatic coffee, high-intensity illumination is one of the effective ways to reduce this phenomenon [1]. However, it may not be suitable for use in an office environment, such as in buildings where there is no way to directly illuminate the sun. Therefore, high color temperature illumination sources offer another option, because high color temperature illumination can improve people's alertness and help us reduce the degree of sleepiness in the afternoon [2]. However, the illumination source we use today can only provide a fixed color temperature (for example, color temperature of 6500K). Exposure to such a fixed illumination source for a long time does not keep the alertness for a long time. Therefore, we need to adjust the different color temperature lighting environment in different time periods for each person's different needs. Therefore, the lamps we need today can not only provide illumination sources with variable color temperature and high color rendering. In order to achieve such a dynamic illumination source, LED is the only choice; because we can arbitrarily select the peak wavelength of the LED, after mixing, we reach such a novel and important biologically significant illumination source. Among such novel light sources, LEDs play a very important role, and after a combination of different LED wavelengths, sunlight can be simulated at different times, including early morning, noon and dusk. The six LEDs selected in this study are the light source modules composed of the six best LEDs after the best selection [3], which is different from the combination of only red, green and blue. The illumination source not only has high color rendering, but also the color temperature can be modulated. After combining these six different LEDs, the color temperature range can be from 1800K to 12000K. The average color rendering coefficient measured by the spectral radiance meter JETI is 88, and the illuminance is higher than 700 lux.
The relationship between alertness and color temperature Previous studies have pointed out that high color temperature sources can cause a higher degree of alertness to humans, and the level of alertness is judged by the alpha wave attenuation coefficient (AAC). Through the brain wave (EEG) signal measurement, the alpha energy ratio of open and closed eyes is obtained [4]. Therefore, the bright natural light that improves the human sleepiness in the afternoon can be replaced by a high color temperature light source. However, after prolonged exposure to high color temperatures, the same level of alertness may not always be maintained. Eight subjects were exposed to a light source with a color temperature of 6500 K for 1.5 hours. The degree of alertness decreases as the time exposed to the light source increases. From this result, it can be known that the degree of alertness is maintained within 30 minutes. When the AAC is high, the light source is illuminated by a high color temperature, and AAC is not increased. The AAC decays after an hour, probably because the eye has been adapted to this color temperature. Therefore, when the degree of lethargy is increased, it may be necessary to irradiate with a higher color temperature light source, or to change to a low color temperature light source. In addition, because different color temperatures may present different levels of alertness and mood, we can adjust the color temperature according to different alertness states. We used different color temperatures to test the alertness. This experiment is a two-day experimental procedure. The illumination control illuminance is 500 lux. The subjects have five men and five women, aged between 20 and 22. The three light sources are represented as a third type of 6500K, a second type of 4000K, and a first type of 3000K. The related AACs show that the 6500K light source on the first day of the test can make the alertness higher than the 4000K or 3000K light source; therefore, compared to the 3000K and 4000K color temperatures, the 6500k light source can suppress the degree of sleepiness in the afternoon, due to different people. The degree of lethargy felt at different time points is different, so different people can request to light different color temperature sources at different times, so that not only can the degree of drowsiness be suppressed but also the work efficiency can be improved.
1 Manufacture of adjustable color temperature LED light source
To reconstruct the illumination source (E) λ can be reconstructed by M LEDs to form a reconstructed source ˆE(λ), which is expressed as follows:
The spectral coefficients of the reconstructed light sources of each LED can be calculated by the following formula [3]:
The reconstructed light source coefficient must be positive, and the above formula A is a sampling of each LED spectrum, and samples are taken from 5 nm nm every 400 nm from 400 nm to 700 nm, so the dimension of A is M×61, and E is the spectral sampling of the light source to be reconstructed, and It is also a sample every 5 nm, so it is a vector of 1 × 61. A+ is the virtual inverse matrix of the A matrix, and its dimension is also M×61. Optimizing the LED combination allows you to reconstruct a minimum spectral energy deviation (Euclidean norm): 
The best effect is that because the LEDs are used to reconstruct the light sources, the reconstruction coefficients of each light source must be positive and cannot be negative. Therefore, we can use the best LED screening method proposed in [3] to select the best LED combination with the best LED combination and the minimum energy deviation and positive reconstruction coefficient.
In order to physically construct the adjustable color temperature lighting, we use the above algorithm to collect 61 kinds of LEDs from various sales LED companies, and select the best 6 LEDs among 61 kinds of LEDs to realize adjustable color temperature illumination. Light, its color temperature can be modulated from 1800K to 12000K blackbody radiation, as shown in the left column of Table 1. In fact, it is not easy to buy LEDs with the same peak wavelength, so we use the closest LED to replace it, as shown in the right column of Table 1, and use these 6 kinds of LEDs to construct an adjustable color temperature illumination lamp whose color temperature modulation range is 1800K to 12000K. The peak wavelength and half-wave width (FWHM) of the six LEDs selected for the best six LEDs and nearly analog are shown in Table 3.1. We use the JETI Spectrometer to measure the color rendering of adjustable color temperature lamps at various color temperatures, all with illumination effects of CRI greater than 88 and illumination greater than 700 lux. This lighting is applied to the effect of home makeup lamp or TV spotlight and is applied to the living room lighting. It needs different color temperature lighting for different needs, especially in the work area. If the lighting is controllable and self-adjusting, it is displayed. With a high degree of lighting comfort [5], this adjustable color temperature lighting can meet this need. In addition, the color temperature box is usually equipped with several standard light sources, which will cause replacement trouble and space. The above six kinds of LEDs are amplified into 12 different color LED modules to meet this demand.
Table 1 Simulating the best 6 LEDs and practical applications
2 Conclusion
General LED high color rendering index mixed light, using red, green and blue three colors or red, green and blue amber and other four colors, can achieve the highest color rendering index of 85, we can use the six color LED to achieve a color rendering index is much larger than In addition, we can construct a color-adjustable LED illumination source, which is different from the currently available fixed and high color temperature lighting fixtures. The illumination source we construct can not only reduce the sleepiness in the afternoon, but also adjust us. The mood can be adjusted according to the different people in different workplaces. Since the color of the LED light source can be modulated and has a high color rendering index, this LED light source can be used in a variety of different applications. For example: color box light source, TV studio lighting. Therefore, in the case of general lighting, we can use the adjustable color temperature illumination source to construct intelligent lighting to replace the general lighting.
Edit: Cedar
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