Beam width

[jawnn]

If the beam is 20 degrees the width at 20ft would be about 7ft wide...but does that include the spill? I need some width at the hot spot.

So is there any lights that can do this....?????
and with out the dark spot????

 

[Steve K]

your math is correct, but the tough part is understanding some descriptions of beams. When I pick out an optic for a light, I look at the manufacturer's datasheet. These usually show a plot of intensity at different angles. This gets me in the ballpark. I'm using some Ledil optics with a 8 degree beam that work well for me on the road. For examples of datasheets, you can poke around Ledil's website:
http://www.ledil.fi/

A 20 degree beam sounds pretty wide for road use (a big assumption on my part), and 20 feet is pretty close. I'm usually more concerned about what is 100 feet ahead.
... but anyway.. if you are trying to use info from a light manufacturer, you really need to know what they mean when they say 20 degrees. Without proper measurement of intensity over a 180 degree (or at least 90 degree) arc, there's no way to really know what the beam is like.

regards,
Steve K.