Comparison between LED and traditional tunnel lighting source LED is a solid-state semiconductor device that can directly convert electricity into light. Compared with traditional road tunnel lighting sources (sodium lamps, metal halide lamps, etc.), LED light sources have the following advantages:
(1) Low light decay: If the heat dissipation conditions are good, the LED is positive light decay in the first 10000h, the first 10000h light decay is 3%-10%, and the first 50,000h is basically 30%, which is much lower than ordinary road lighting sources. Luminescence is more stable.
(2) High color rendering: general LED color rendering is about 70 to 80, if three primary color phosphors are used, it is higher; general high pressure sodium lamp is 20 to 35, low pressure sodium lamp is lower, so even the traditional light source brightness Higher than LED, but the visual effect is worse than LED, "not the brightest, but the clearest to see" This should be a direction for the development of LED light source applications.
(3) Lifespan: The lifespan of LEDs is higher than that of general road tunnel lighting sources, and is now generally higher than 50000H.
(4) Price: Although the current price of LED lamp holders is higher than that of traditional lighting fixtures, with the maturity of manufacturing technology, their prices are currently falling sharply. The price of a set of high and low pressure sodium lamps is generally around 2,000 yuan, and its cables and other auxiliary The price of parts is higher than the cost of LED cables.
1 brightness
Because the brightness outside the tunnel during the day is much higher than that inside the tunnel, when the driver enters the tunnel, the vision needs to have a certain adaptation time before being able to see the situation inside the tunnel clearly. This phenomenon is called "adaptive hysteresis" "If there is no proper transition, a black hole phenomenon will occur, causing the driver to temporarily lose normal visual functions, which will bring certain safety hazards. The black hole phenomenon is a visual problem that occurs before entering the tunnel, and it is also the most important problem in tunnel lighting. For this reason, tunnel lighting is usually divided into entrance lighting, interior lighting and exit lighting. The brightness of the tunnel entrance lighting during the daytime should be determined according to the brightness outside the tunnel, the speed of the vehicle, the field of view at the entrance and the length of the tunnel. The threshold period is to eliminate the "black hole" phenomenon, and the lighting level in the transition period further gradually decreases, thereby providing the driver with time for visual dark adaptation.
2 brightness uniformity
Good visual function not only requires a good average brightness, but also requires that the average brightness on the road surface and the minimum brightness cannot be too different. If the brightness difference in the field of view is too large, the bright part will form a dazzling light source, and the change of brightness and darkness will bring a certain stroboscopic effect, and then affect the vision, the visual effect of the human eye will be significantly worse, and the vision Fatigue will also increase.
The overall brightness uniformity U0 refers to the ratio of the minimum brightness to the average brightness on the road surface of the tunnel inner section, and the longitudinal uniformity U1 refers to the ratio of the minimum road brightness to the maximum road brightness on the axis of the lane. If there are continuous and repeated bright and dark bands on the road, the "zebra effect" will be very irritating for road users traveling in this lane. This problem involves human psychology, but it also endangers road safety. The longitudinal uniformity is mainly used to evaluate the size of the "zebra effect".
3 glare
The formation of glare is due to the presence of extremely high brightness or brightness contrast in the field of view, which reduces visual function or makes the eyes feel uncomfortable. The glare in the tunnel lighting can come from the headlights of oncoming vehicles, tunnel lighting fixtures, and the high brightness outside at the exit of the tunnel. Glare will reduce people's ability to recognize obstacles and endanger driving safety. Tunnel lighting fixtures should adopt a cut-off type, and take special technical measures to eliminate direct and reflected glare to form diffuse reflection, so that the light can enter the human eye very softly. The International Commission on Illumination has adopted a relative threshold increment (TI) to account for the decline in visual function caused by glare, which is a measure of disability glare. In the European Standards Committee's tunnel lighting standard (CR 14380: 2003E), the provisions for disabling glare are as follows: The relative threshold increment (TI) must be less than 15% in the tunnel threshold section and internal section during the day and the entire tunnel at night. .
4 stroboscopic effect
Stroboscopic refers to the discontinuity of the arrangement of the illuminators in a long tunnel, so that the driver is constantly stimulated by the change of light and dark, which causes annoyance. It is related to the brightness change of light and dark, the frequency of light and dark changes, and the total time of strobe. These three factors are related to the optical characteristics of the lamps used, the speed of the vehicle, the distance between the luminaires, and the length of the tunnel. Generally speaking, the stroboscopic phenomenon brought by the frequency of stroboscopic less than 2.5 and greater than 15Hz is acceptable.
If the vehicle speed is 60km/h, that is 16.6m/s, and the installation distance of the lamps is 4, the frequency of the strobe is about 4.2Hz. When designing, it should be considered and choose the appropriate installation distance of the luminaire. If the frequency of the strobe is between 4Hz and 11Hz, and the duration exceeds 20s, it will bring obvious discomfort to the driver.
5 lighting control
Advanced lighting control methods are important techniques for reasonable energy conservation while ensuring visual conditions and meeting the requirements of tunnel lighting. The purpose of lighting control is to change the lighting level of the tunnel at any time. Due to cloudy, rainy or dusk, the brightness outside the tunnel entrance is much smaller than usual, so appropriate measures must be taken to reduce the level of illumination at the entrance section to reduce unnecessary energy waste. In tunnel lighting, various dimming equipment or control devices can be used to adjust and control the illumination of the tunnel lighting environment or the turning on and off of lights according to factors such as day, night, and traffic volume. At present, most foreign countries use photosensitive devices and dimmable electronic rectifiers to form intelligent lighting systems to reduce the overall brightness of the lamps in the tunnel and reduce energy consumption; at the same time, the uniformity of the tunnel brightness is maintained.
