Solar Lights Manufacturers: Medium Solar Street Lights Designing

By Author: James Mathews
Total Articles: 20
Comment this article

Over the last few years, LED street lights manufacturers have turned solar street lights into real products that can be seen on the road. Solar Lamps make sense for many reasons, such as their compact size, greater efficacy (lumens per watt), durability, and robustness. LED sources have given the flexibility for interesting new designs with slimmer profiles as compared to traditional metal halide arc lamps.

Solar Street lights systems are designed in a manner to enhance the safety for pedestrians and for vehicles both. Visibility of obstacles on the road surface and in potentially dangerous situations where roads are crossed by other vehicles or pedestrian crossings is guaranteed and are in accordance with technical standards and laws.

Pole-mounted solar lamps are the traditional technical solution for solar street lights. This give the advantage of using the best lamps in terms of tone and colour rendering, as well as maximum light efficiency, resulting in big saving in energy consumption.

Application of LED by the LED street lights manufacturers in solar street lights is a response to the need to improve ...
... the light quality and save energy. Best LEDs are selected from the top performing ones in terms of efficiency, durability, energy saving potion, color enhancements and brightness. The distribution of the light depends upon the type of traffic and features of the road. The optics used for street lighting luminaires distribute the light based upon the number of lanes and their sizes, whether it is motorway, major roads, city roads or narrow roads and several other factors.

How Street Lighting Calculations Are Performed:

It is assumed that the solar lamps are far away from the surface of the road that they illuminate. To calculate the test metrics for them, their intensity distributions, positions, and orientations are the data which are required. Summed illuminance at any point on the road for all the installed lamps are calculated by the LED street light manufacturers on the basis of the intensity distribution. The luminance calculations are performed based on the factors such as the angle of light coming from the lamp and striking the roadway as well as the angle of the standard observer. Then, a table of reflectances for those angular coordinates, called the RTable, is interpolated to find the correct reflectance of the roadway and the luminance observed.

Next step is to design the solar street lights geometrically. But before we can design the lamp geometry, we need to define a source model. There are many suitable, high-brightness LEDs on the market, some of which are specifically sold for street lighting applications. In addition to the specifications sheet, the manufacturer provides a CAD model of the LED exterior, as well as ray files, the intensity distribution, and other pertinent information.

Designing the Medium Street Lamp:

Equipped with the perfect model of the LED, next move is to create solar street lights. The IESNA (Illumination Engineering Society of North America) lighting handbook provides classification definitions for different types of street lamps. Though it is not the detailed description of how to create the desired solar lamps but it does gives a brief for understanding the type of layout one might want to work with for a given lamp. In Medium longitudinal classification solar street lights, the term medium refers to how many mounting heights away from the lamp the intersection of the maximum intensity point along the length of the roadway is. We assume that the road is a two lane roadway, with each lane being 3.5 meters in width. The intersection needs to be between 2.25 to 3.75 mounting heights away. The locus of intersection points needs to fit within 1 mounting height in each direction towards the sides of the road. The intensity points directly along the roadway and not the bending.

Designing the Optics:

For a typical LED street light, manufacturers like to have some light directly below the solar lamp, sometimes even if most of the light for the lamp is diminishing at larger angles. Solar street lights in India uses two types of optics- one spreads a small amount of light directly below the lamp and other makes a high angle distribution. TIR optics is the most preferred one because of its higher efficiency and controlling more optical surface. Best material used by most of the manufacturers is the PolycarbonateLED2045 for all the optics. Similarly we work on the wide spread optics to get the peak of the intensity distribution strike the road. We again refer the IES classification and select the angle for the desired lamp post height.

Now since the required wide spread and low spread solutions have been achieved, both of them are clubbed together to form a total luminaire distribution. Both LEDs are placed together on the same circuit board plane. Then a second recessed reflector is added for the low spread optic. This will catch any light that that comes out at high angles and allows the optic to penetrate the metal sheet. Once both the optics are designed, the total flux is optimized for all low spread and high spread optics combined in conjunction with the roadways parameters to meet the design requirements and specifications. Finally a full luminaire is constructed and re-verified that the design meets the specifications.

The article has been published by solar lights manufacturers in interest of the public in order to make public the process how solar street lights are designed. The above designing process given by the LED street light manufacturers is just a glimpse of the process and not the complete details. The intention of this article is to just give a brief overview of solar lamps construction.