LED street light reflector bowl and lens type secondary optics

LED lighting will be widely used in road lighting first. This inference is based on the characteristics of LED such as long life, high efficiency, and high light utilization. Many people have made many attempts to apply LED in road lighting, but it is not difficult to see that LED street lights have not been well developed in the past two or three years. The reasons are: high cost, short life, and poor lighting effect (poor uniformity). Fortunately, the upstream industry has developed rapidly, and the improvement of LED chip light efficiency and the reduction of prices have made LED road lighting closer and closer. Professional optical design has also greatly improved the lighting effect. More manufacturers are also making such attempts. This article proposes a new optical solution-independent unit reflector, aiming to find a new LED road lighting solution for people.

Compared with lenses, reflectors have the following characteristics: low cost, high efficiency and easy assembly.

The common lens material is PMMA. The transmittance of PMMA material with current technology is only 94%. After being made into a lens, there will usually be more additional light loss due to the effect of refraction and reflection. The following example illustrates:

A light source is set up to generate 50,000 rays:

When there is no PMMA transparent plate, the efficiency is 100%. Now set an ideal PMMA transparent plate in front:

The efficiency becomes 94.337%.

(Note: 16808 Rays appear in the figure because a ray passing through the interface between PMMA and air may be refracted and reflected at the same time, thus increasing the number of rays, but causing a certain loss in terms of energy.)

If PMMA material is made into a lens, the loss will be even greater. The following is an example of a common PMMA material lens on the market (considering that there is always light leakage from the back of the lens, and in fact the light leakage cannot be used, a fully absorbing substrate is set at the back of the system to enhance the rigor of the data):

Lens appearance:

Analysis of stray light after light passes through the lens:

The actual efficiency of this lens is only 86%

Reflective optical systems are relatively easy to analyze. By analyzing the light energy distribution of the light source, suitable lenses for road lighting can be designed through redistribution.

The light source has a Lambertian light emission mode (i.e. the common Lumileds, CREE, Edison LED), combined with a designed reflector, with two light emission angles of 50 and 120 degrees respectively. That is, a street lamp placed on a 10-meter pole can form a uniform light spot of about 12×30 meters on the ground. The number of units can be increased/reduced according to the illumination requirements.

1. Light Trajectory:

2. Single 1W lighting effect diagram (illuminance distribution):

3. The following is a simulation of the lighting effect of a section of road:

The road is 15 meters wide, with symmetrical lights, 10 meters high poles, 32 meters pole spacing, 5 degrees installation angle, and 1.5 meters cantilever length. The road surface illumination is uniform, 90% of the light is concentrated on the road, and the roadside illumination gradually decreases. There is no hard light edge, which will not cause visual discomfort to drivers.

Efficiency analysis:

The light irradiated by the reflective system is divided into "direct light" and "reflected light", that is, part of the light does not need to be directly scattered by the reflective wall, while the other part of the light passes through the reflective wall and irradiates to the corresponding position.

Set the reflection wall to "Perfect Absorber", and then based on the emission efficiency, you can get how much light does not need to be directly illuminated by the optical system:

It can be seen that 41.88% of the light in the optical system is directly irradiated without passing through the optical system, that is, the energy loss is 0, and another 58.12% of the light needs to be reflected by the reflective wall. The reflection efficiency depends on the reflective wall material and processing technology. By plating enhanced aluminum film or silver mold, the reflection efficiency can reach more than 90%, so the reflective system efficiency can reach and exceed the following values:

41.88%+58.12%×90%=94.19%

This is much higher than the 86% efficiency of the lens method, that is, we can utilize 94.19 to 98.84 lm of 100 lm of light.

The biggest advantage of this reflective bowl is its high efficiency. The light source used is an LED with the common Lambertian light output mode. This effect is achieved by a single light source rather than an arrangement or combination, so the number of LEDs can be increased or decreased according to the power requirements of the street lamp.