In-depth analysis: LED design standards for lighting engineering applications

The sales distribution statistics of LED products in major application fields in 2008 show that architectural landscape is the largest application field of LED in my country, accounting for 28% of the total market share; LED display screens and home appliance displays are the second largest application field, accounting for 27% of the total market share; small and medium-sized backlight sources such as mobile phones and notebooks are the third largest application field, accounting for 22% of the total market share; traffic lights, car lights, special lights and other applications occupy a certain market share.

In the future, with the holding and preparation of major events such as the 2010 Shanghai World Expo and the Guangzhou Asian Games, as well as the acceleration of urbanization, the application of LED in the field of landscape lighting will further increase, and the market application space of LED display screens will continue to expand. As LED continues to mature, backlight sources for mobile phones, computers, traffic signals and indicator lights, automotive lighting, and special lighting such as flashlights, mining lamps, explosion-proof lamps, and beacon lights will become important application markets, and the application market structure of LED will also undergo major changes. According to the National Semiconductor Lighting Engineering Research and Industry Alliance, it is expected that in 2010, the overall scale of my country's semiconductor lighting market will reach about 100 billion yuan, the market scale of LED backlight sources will exceed landscape decorative lighting, becoming the largest application field, and the market scale of functional and general lighting will also grow rapidly. It is expected that the average annual compound growth rate from 2010 to 2015 will reach 40%, and the industry scale will reach more than 500 billion yuan in 2015.

Forecast of major application markets of semiconductor lighting in my country in 2010

2. Performance and characteristics of LED

2.1 Low energy consumption and small size As a solid light-emitting device, LED has low power per piece. Currently, the most widely used ones are less than 0.5W, and the power type is also between 0.5W and 1.0W. In addition to the advantages of LED in terms of size, its small size, light weight and thin thickness have greatly expanded its application space. It is very suitable for backlight and display system applications. In the field of traditional lighting, it also makes the design more flexible and diverse, and the light easier to control.

2.2 Energy-saving LEDs have been developing rapidly since their birth in the 1960s, following the "Haitz Law" that brightness increases 30 times and price drops 10 times every 10 years. It is reported that the current laboratory data of white light LED luminous efficiency has exceeded 160lm/W, and the power type white light LEDs entering the commercial field have also reached 100lm/W. With the breakthrough of key technologies, the luminous efficiency of power type LEDs will still have a lot of room for improvement in the future, and may reach up to 200lm/W.

2.3 Rich and lifelike colors, varied graphics Different chip materials can produce different monochromatic LEDs; and the same chip material can produce different light colors of LEDs grown in different epitaxial wafers. As long as there is a slight change in the chip alloy composition, the light color of the LED will change significantly. In theory, various monochromatic and white light LEDs can be obtained within the visible light range.

2.4 Long life The solid-state LED is different from the general thermal radiation light source or gas discharge light source, which has a fragile bulb and a filament that is easy to break. Its structure is firm and generally will not break or burst during use. It has safety protection and a long life. The life of a general LED can theoretically exceed 50,000 hours, which is an order of magnitude lower than that of traditional light sources. Its application in lighting projects can greatly reduce maintenance costs.

2.5 Good shock resistance The structure of LED is mainly composed of PN junction chip, electrode and optical system. It is an electroluminescent light source. Its structural characteristics determine that the impact of vibration on it is relatively small.

2.6 Safety LED is a low-voltage device. The voltage to drive a single LED is only 2.5~3V, and the driving current is tens of milliamperes. It will not cause electric shock accidents, so it is relatively safe. It is also suitable for places with low-voltage power supply, such as car compartment lighting in cars and trains, and can be used in conjunction with solar power generation devices.

2.7 Environmentally friendly LED lighting devices are different from high-intensity gas discharge lamps, such as fluorescent lamps, fluorescent high-pressure mercury lamps, etc. The inner wall is coated with fluorescent coating, including the post-use treatment of fluorescent powder, which causes pollution to people and the environment. LED lighting devices do not add mercury, so pollution is reduced.

2.8 Fast response The principle of electroluminescence gives LED a response time of only a few milliseconds, allowing LED to reach full light output in an instant, which has a strong advantage as a signal lighting. Combined with its color diversity, LED products are easier to control color and brightness, so they can be used in many fields that require control.

3. Design standards for lighting engineering applications in my country

Saving energy, protecting the environment, and improving lighting quality are the purposes of our implementation of green lighting. The premise of energy saving is to meet people's normal visual needs, that is, to meet the requirements of lighting design standards. We should not blindly emphasize energy saving and reduce the requirements for the quantity and quality of lighting. The standard system for engineering construction in my country is relatively well established, and different lighting places have formulated or are formulating corresponding design standards. These standards are formulated for people's visual work needs, have certain scientificity and feasibility, and try to be close to international standards, and have certain advancement.

Table 2 my country's lighting design standards

4. Classification of lighting and applicability of LED

In my country's lighting design standards, different lighting methods are classified according to their characteristics in different lighting places.

Table 3 Lighting classification and LED applicability standards

5. Requirements for lighting devices in different lighting locations

The lighting evaluation indicators specified in this standard include: maintaining average illuminance value on the working surface or reference plane, illuminance uniformity, unified glare value, color rendering index of the lighting source, and correlated color temperature.

In addition to the above requirements, other requirements for lighting devices are:

Requirements for the shading angle of lamps:

Table 4 Shading angle of direct type lamps

The lighting of workplaces with visual display terminals should limit the brightness at an altitude angle equal to or greater than 65° above the mid-perpendicular line of the lamp. The average brightness limit of the lamp at this angle should comply with the provisions of Table 5.

Table 5 Average brightness limit of lamps

The color table of indoor lighting sources can be divided into three groups according to their correlated color temperature. The recommended values ​​of correlated color temperature are shown in Table 6:

Table 6 Recommended values ​​of correlated color temperature

5.2 Urban Road Lighting Design Standards

Evaluation indicators of urban road lighting: The evaluation indicators of motor vehicle traffic road lighting should be the average road surface brightness, total road surface brightness uniformity and longitudinal uniformity, glare limit, ambient ratio and induction; the evaluation indicators of pedestrian road lighting should be the average road surface illuminance, minimum road surface illuminance and vertical illuminance.

Table 7 Standard values ​​of road lighting for motor vehicle traffic

In addition to the above requirements, other requirements for lighting devices are:

Expressways and trunk roads must use cut-off or half-cut-off lamps; secondary trunk roads should use half-cut-off lamps; and branch roads should use half-cut-off lamps.

5.3 Technical Specifications for Urban Night Lighting

Evaluation index of urban night scene lighting: The evaluation index of lighting for buildings, structures and other landscape elements adopts brightness or a combination of illuminance. The evaluation index of lighting for outdoor public spaces such as trails and squares adopts ground horizontal illuminance and semi-cylindrical illuminance at 1.5m above the ground.

Evaluation of advertising and sign lighting: The maximum allowable value of the average brightness of advertising and sign lighting in different environmental areas and different areas shall comply with the provisions of Table 8; the illumination uniformity U1 of external projection advertising and sign lighting should be 0.6~0.8; when advertising and signs are illuminated by external projection, the projection range should be controlled, and the scattered light outside the advertisements and signs should not exceed 20%; the light pollution of the surrounding environment caused by advertising and sign lighting should be limited, and should comply with the provisions of Article 7.0.2 of this specification.

Table 8 Maximum allowable average brightness of advertising sign lighting in different areas and different areas

The restrictions on light pollution shall comply with the following provisions: the vertical illuminance generated by night lighting facilities on the outer surface of residential building windows shall not be greater than the value specified in Table 9; the luminous intensity of night lighting fixtures in the direction of the living room shall not be greater than the value specified in Table 10; the threshold increment of glare generated by non-road lighting facilities on urban roads to car drivers shall not be greater than 15%; night lighting facilities in residential and pedestrian areas shall avoid causing glare to pedestrians and non-motorized vehicles. The glare limit value of night lighting fixtures shall meet the provisions of Table 11; the maximum value of the upward luminous flux ratio of the fixture shall not be greater than the value specified in Table 12; the average brightness generated by night lighting on the building facade and sign surface shall not be greater than the value specified in Table 13.

Table 9 Maximum allowable vertical illuminance on the exterior surface of windows in residential buildings

Table 10 Maximum permissible values ​​of luminous intensity of night scene lighting fixtures facing the direction of the room

Table 11 Glare limit values ​​for night scene lighting fixtures in residential and pedestrian areas

Table 12 Maximum permissible values ​​of upward luminous flux ratio of lamps

Table 13 Maximum allowable average brightness of building facades and sign surfaces

6. Conclusion

In summary, LED has the advantages of energy saving and long life, and has been widely used in backlighting, display lighting and landscape lighting. When LED is used as a lighting device for general lighting, it must also meet the requirements of lighting design standards for general lighting. In fact, people tend to pay too much attention to the characteristics of LED energy saving and long life, but ignore other comprehensive requirements of general lighting in terms of lighting quantity and lighting quality, especially some performance and characteristics of LED, such as: concentrated light and high peak light intensity, which will become weak points in general lighting, because concentrated light and peak light intensity will bring serious glare and damage people's vision if they are not solved well. Therefore, in order to make LED widely used in general lighting, it is necessary to meet the comprehensive requirements of lighting design standards for lighting objects. Only by meeting the comprehensive requirements of lighting design standards can the development of LED be better promoted.