In any lighting application, a reflector is an element that helps to control light that is emitted from a source. For example, to redirect light from directions where it is not useful and focus it on the direction where it is useful.
Since LED COB arrays emit light in a Lambertian pattern, a reflector is required in applications that demand a beam narrower than 120° FWHM. The most common types of reflector geometry used in SSL systems are parabolic, hyperbolic, and elliptical zonal. Each of these geometries is suited for particular illumination patterns.
For example, parabolic reflectors typically generate a narrow beam pattern and hyperbolic reflectors produce a wider beam. Parabolic reflectors are often used for omnidirectional light sources such as incandescent, CFL and HID which are designed to spread light in all directions. A parabolic reflector is an effective way to redirect light down and out of the fixture. But parabolic designs are not well suited for applications requiring unidirectional light or uniform beam spread with minimal glare, such as workplace task lighting.
Elliptical reflectors work by placing the light source at one focus of the ellipse which then concentrates the light down to a point located at the other focus of the ellipse. Elliptical reflectors are widely used in illumination to concentrate the light of a source in a secondary focal plane. In other words, to shape the light into a more focused beam, such as a spotlight.
A hyperbolic shaped reflector causes light from the LED to be reflected and spread more like a convex lens. It produces high lumens with increased efficiency and reduced glare. A hyperbolic reflector design can eliminate the need for a diffusor to soften light output, thus can increase the efficacy of the luminaire by as much as 35 percent.
Reflector Performance
In terms of performance, reflectors are characterized in two ways:
- Beam width – the angular distribution of the light emerging from the source.
- Beam efficiency – how much light from the source is directed into the beam at a particular angle.
Lighting designers specify reflector efficiency in units of candelas per lumen (cd/lm) The candela is the base unit of photometry and is defined as 1 lumen per steradian and quantifies the luminous intensity of beam of light emanating from a source.
The definition of the candela can also be stated as photometric power per solid angle. Thus, a reflector’s efficiency can be thought of as the ratio of how many lumens end up in the beam to how many lumens are provided by the source per degree of solid angle. For this reason, the beam efficiency will change over the angular distribution of the beam. Typically, the beam efficiency is specified at the 0° viewing angle.
Typical categories used in general lighting are spot, flood and medium. These categories are defined by the width of the beam produced by the combination of light source and reflector. Typically, this definition depends on the angular width of the beam at 50% of maximum intensity. Again, the metric of “full width at half maximum” (FWHM) is used however this definition is not to be confused with the FWHM of the intensity vs. wavelength description of the LED’s spectral distribution.
Diffusers and LED COB Performance
To some degree, all materials scatter light in various directions as photons travel through and/or reflect off them. Diffusers are materials used in lighting systems that are particularly suited for scattering light that passes through them. Diffusers help to “soften” lighting by directing light in random directions, which results in a wider dispersion of light and a less defined appearance to the lighting source.
Diffusers can also come at a significant cost to the lumens budget of the lighting system (i.e., they reduce the brightness, and correspondingly reduce efficiency). However, designers of some applications often deem this cost worthwhile due to the improved appearance and visual appeal of the lighting.
Learn more about Design Guidelines for LED COB Arrays
--------------------------------------------------------------------------------------------------------------------
Luminus Website https://www.luminus.com/
Luminus Product Information (datasheets): https://www.luminus.com/products
Luminus Design Support (ray files, calculators, ecosystem items: [power supplies, lenses, heatsinks]): https://www.luminus.com/resources
Luminus Product Information sorted by Applications: https://www.luminus.com/applications
Where to buy Samples of Luminus LEDs: https://www.luminus.com/contact/wheretobuy.
Comments
0 comments
Please sign in to leave a comment.