By BizLED Bureau
Dec 6, 2015: As LEDs are directional light sources, designers usually require secondary and tertiary optics to meet various requirements as per different applications. Optics are components that are used to control light output. There are three types of LED optics:
Primary optics, which is usually attached directly to an LED; it is a part of the LED package. When lenses are integrated into the LED package, particularly in SMT and power packages, it is called primary optics. These help the luminous flux of the LED to take a specific radiation pattern.
Secondary optics are attached directly onto or around the LED. Secondary optics are usually mounted on a holder which is placed over the LED package. For example, if an LED has a 90-degree viewing angle, and a different beam shape and angle are required for a particular application, the secondary optics are used to get that angle. Here reflectors are used as secondary optics that can manage reflected light. Secondary optics collimates the beam angle to 5°-15°.
Secondary optics deliver light beam that has large optical viewing angle and circular cross-section. Reflectors are usually fitted on lenses to improve the light beam. This gives out focused light.
Tertiary optics are external components. They are used as per the requirements of different applications. Tertiary optics or diffusers usually help to diffuse, direct, and transport light. Some common tertiary optics are light guides, light pipes and total internal reflection (TIR) devices. LEDs can be modulated by controlling the operating current of tertiary optics.
In this article, we will talk about secondary and tertiary optics.
Why secondary and tertiary optics are required?
Secondary and tertiary optics dictate the photometric performance of LED lamps and luminaires. Secondary and tertiary optics are used in different applications like street lighting to direct the LED light beam angle perfectly without wasting any light.
Secondary and tertiary optics are usually required for proper performance of lamps and luminaires?hence, it justifies the cost of the products.
The radiation that falls from an LED with a primary optic is generally as wide as 80°?90°, which is directional if actually compare with an incandescent bulb. In an application, where the target plane of lighting is more than a distance of 0.5 m, LEDs directional light is not sufficient. Here a designer should use a secondary optic such as a total internal reflection (TIR) lens or a reflector to collimate the light beam to a distance of about 3.5°?15°. Designers also use a tertiary optic like a diffuser to improve spatial uniformity , color, and to customize the beam to suit photometric needs.
It is found that if a designer skips the use of secondary and tertiary optics while designing lamps and fixtures, the designer faces many performance and integration issues at the project?s implementation stage.
Benefits of using secondary and tertiary optics
Tertiary optics offer several benefits while designing LED lamps and luminaires. For example, these optics are used GE?s LED PAR38 lamp, where there are secondary optics like reflector and the lens. LED recessed downlights and MR16-lamp also have reflectors as secondary optics which help to collimate the radiation from the LEDs. LED recessed downlights also have diffusers as tertiary optics, which enhances the beam angle of the light. In MR16 lamp, Soraa uses an TIR-based collimator.
In short, the main benefits of using secondary and tertiary optics are flexibility in design, required angle of light, as well as reduced cost.
Some other major benefits are:
If a diffuser is integrated into the product design from the beginning, there will be no need to redesign the secondary optics if a project requires a different beam angle of light.
If just one reflector or TIR secondary optic is required, then only one mold needs to be manufactured, instead of many. This will reduce the inventory costs due to a single stock keeping unit (SKU).
With a diffuser, the same fixture can be used in multiple installations.
Many a times, designers face the issue of non-uniformity in color or intensity at the target plane.
Today, it has become simple to design with secondary and tertiary optics. One of the common tools used by the designers to develop lamps and luminaires is the optical and lighting simulation software. Earlier, it was difficult to model the behavior of tertiary optics in the past. Today packages like TracePro from Lambda Research, LightTools from Synopsys, are now compatible with bi-directional transmittance distribution function data, which describes how a ray of light behaves after entering and exiting a diffuser.
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