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Discussion in 'Landscape Lighting' started by starry night, May 25, 2011.
Stupid question #459. Just curious. How are varying beam spreads engineered into LEDs?
just like on halogen, it is the reflector. dig around on candlepowerforums.com on the homemade and modified flashlight discussion and you'll find folks that build and switch out different reflectors and led's to achieve different beam spreads. manufacturors do the same thing on factory LED's.
Thanks for the answer, David. It just didn't appear that there was a reflector like I would see in a halogen.
it is a somewhat different reflector than halogen. and different LED's have different factory exit beam spreads before it ever hits the reflector. for example, a narrow spot reflector would be nearly mirror smooth, while a floodier reflector would be really faceted. an orange peel finish on a reflector would be somewhere in the middle, some flood and some throw.
I may not use the correct terminology. I am not sure if I read these terms or whether I pulled them out of the depths of my brain but ...........do I understand correctly that each diode (facet?) of the LED luminaire (the array?) would have its own reflector? Or are the facets grouped in front of one reflector?
LED optics are quite different from incandescent due to the way the diode emits light and where it's positioned.
The great majority of LED MR-16's don't use reflectors mainly because they lack precise control over beam pattern; also because of space constraints in multi-chip arrays.
Incandescents work with near-parabolic reflectors because the filament is postioned inside the parabola at its focal point. An LED chip sits on a board so it can't be positioned in a place that takes advantage of parabolic reflection. The LED's that do use mirrored reflectors are likely to have beam patterns quite different from those of incandescents.
Instead, they use Total Internal Reflection (TIR) optics. These are the clear acrylic or polycarbonate lenses that you see in most LED MR-16's. They are precisely engineered to use a combination of internal reflections and columnar optics that result in optimal beam patterns.
Thanks Steve. the TIR is what I was trying to understand by looking at an LED array and not seeing what I would describe as a reflector.