Related Indicators of LED Street Lighting Design Guide
As the main purpose of Road Lighting Design is to provide a safe and comfortable visual condition for motor vehicle drivers, all the quality indicators of LED road lighting will be considered from the driver's point of view. The main evaluation indicators of LED street lighting design guide are as follows.
(1) Average brightness and average illuminance of pavement. Considering the driver's visual function, their judgment on the road surface depends largely on these two illumination parameters. Because the human eye is in the intermediate visual state in the night and the sensitivity of the color difference is weakened, the brightness of the road affects the contrast sensitivity of the driver's vision.
(2) The uniformity of the road surface brightness. If the brightness uniformity cannot be guaranteed, the visual area of the higher road surface will be likely to produce glare! And the dark areas will produce dark area of vision so that drivers can’t identify obstacles and security risks occurred.
(3) Glare Restriction. Glare is caused by a very high brightness or luminance contrast within the visual range. Glare is generally divided into the disable glare and discomfort glare. The former affects the human body's visual function, but the human eye does not necessarily feel uncomfortable; The latter does not necessarily affect the visual performance, but make the eye feel uncomfortable.
(4) Surrounding Ratio. Also known as Ambient Illumination Coefficient, is used to evaluate the brightness of road and the surrounding environment. The SR is defined as the ratio between the average illuminance in the 5m wide area of the roadside and the average illuminance of the 5m wide area within the road by the roadside. If the width of the road is less than 10m, the general width of the road is computed. Under normal circumstances, SR>0.5 is required.
The driver's visual state depends mainly on the average brightness of the road, but the ambient light of the road will interfere with the general condition of the eye. When the road environment is brighter, the contrast sensitivity of the eye will decrease, which needs to improve the average brightness of the road. And in the darker environment, the driver adapts to the brighter Road area and its vision is difficult to accept the objects around the dark area. In this case, lighting needs to take into account the adjacent areas of the roadside and reduce glare.
(5) Visual Inductivity. This is a measure for drivers and pedestrians to quickly perceive the direction of the road ahead under the maximum allowable speed of the road and within a certain distance. The visual guidance is limited to the light of the car's headlights on the road that is not illuminated at night. To improve the visual inductivity, the LED street lamp should be tightly arranged along the road.
In order to prevent the wrong guidance, we should pay attention to the following LED street lighting design guides:
• On the road with a central divider and separate lanes, it is advisable to place the lamp-posts on the central divider to facilitate visual guidance.
• At the corners, the lamp poles should be arranged outside the corners to help clear the direction of the road.
• Using different colors of LED light sources on different roads can clearly indicate different paths and thus improve the guidance.