Due to the layout of the building, most of the high-rise office space also needs artificial lighting during the day, and lighting power has become one of the main energy consumption of office space. Relevant research shows that the lighting energy consumption of office space accounts for 20% ~ 35% of the total energy consumption of the building, and office space lighting has become an important part of energy saving and emission reduction [1, 2].
LED is called the fourth-generation illumination source or green illumination source. It has the characteristics of energy saving, environmental protection, long life and small size. It has been widely used in various fields such as indication, display, decoration, backlight, general illumination and urban night scene. . As LED luminous efficiency continues to increase, and prices gradually decline, the advantages of LED light sources in general lighting are gradually emerging. In recent years, the application range of LED in office space has gradually expanded, and has gradually entered the application field of functional lighting from decorative lighting. The development of LED technology will gradually become an ideal light source for office space.
2 Office space lighting requirements and development trends
Illuminance, brightness, color rendering index, etc. are the basic quantitative indicators that must be considered in office space lighting design. These indicators are specified in detail in C IE (International Commission on Illumination) and lighting design standards in countries around the world. Table 1 shows the relevant regulations of China's lighting standards. Researches on the visual effects of office space over the years have shown that office space lighting quality is also affected by other relevant factors, such as color temperature (light color), brightness distribution and so on. [3, 4] Therefore, the design of office space lighting in recent years has not only been limited to satisfying simple quantitative indicators. The design focus has gradually shifted to how to use the appropriate brightness distribution, spatial atmosphere performance, combination of different light colors and automatic adjustment. Light to meet people's psychological needs for the lighting environment.
3 Feasibility analysis of LED lighting in office space
In office space lighting applications, LEDs must first meet existing lighting specifications and meet people's requirements for visual comfort.
(1) Illumination level
Regardless of the source of light, the illuminance value is one of the first indicators that must be met. Generally, the floor height of the office space is relatively low. Generally, the height of the high-rise office building is 2.6m, and the height of the multi-storey office building is 3.0~3.5m. It is more suitable for applying LEDs with shorter illumination distances. For LEDs with increasing light efficiency, 300 lx or 500lx is not an unattainable target.
In 2007, we conducted a lamp replacement experiment in a standard conference room in the Sino-French Center Building of Tongji University (see Figure 1). Replace the original 414W fluorescent grille with a 251W LED recessed luminaire (see Figure 2). Due to objective factors, the number of lamps cannot be increased. Only the original lamp position can be changed. The average illumination level (0.75m) is reduced from 235 lx to 164 lx. At a 55% reduction in power, the illuminance level is reduced by 30%. Its LED chip has a luminous efficacy of only 45 lm /W, and the efficacy of the current white LED has greatly exceeded this value, which can fully meet the illumination requirements of office lighting. For example, the new office building completed by Japan Izumi Electric (IDEC) in March 2008 and the lighting of the office building of the Zhongli Insurance Company completed by Philips in July 2008 have all adopted LED lamps. The latter consists of 12 or 16 2.6 watt high-power LEDs with a desktop illumination of 500 lx and an overall average illumination of 300 lx. China's Nanjing Henderson Company's service center building also uses LED lighting, and so on.
(2) Glare control
The current indicator for glare control in China is the unified glare value ( UGR). The formula is as follows. UGR = 8 log [ ( 0.25 / Lb ) (La2 /P2 ) ] The national standard appendix explains that the formula applies to general lighting devices in simple cubic rooms; the solid angle of the illuminating part of the luminaire to the eye is 0.1sr>W > 0.0003sr case; and the same type of lamps are evenly spaced; the lamps are double symmetric light distribution. The application of LED luminaires in the conference room of Tongji Zhongfa Center meets the application conditions of this formula.