Lens Degree and mounting height

piranhaman00 · Mar 14, 2022

Hi, can someone direct me to the math and or rational behind lens angle, mounting height and spread?

Im using this little known led with 107 degree reflectors and I have them mounted 6” off water, I’m wondering what type of spread they are getting?

blaxsun · Mar 14, 2022

A PAR meter would be able to tell you with a fair degree of certainty.

jdmee · Mar 14, 2022

I always thought it was basically TAN(Angle/2)

So and lens with a 107 degree beam angle would produce, at 6" off the water, a circle with a diameter of about 16". With the outer part of the circle being around (I think) 50% of the brightness of the center.

https://www.ies.org/definitions/beam-angle/

piranhaman00 · Mar 14, 2022

jdmee said:
I always thought it was basically TAN(Angle/2)

So and lens with a 107 degree beam angle would produce, at 6" off the water, a circle with a diameter of about 16". With the outer part of the circle being around (I think) 50% of the brightness of the center.

https://www.ies.org/definitions/beam-angle/

That would be at the surface of the water correct? What about 10” down? Can you show the math;)

jdmee · Mar 14, 2022

If your angle is 107,

1/2 * 107 = 53.5

TAN (53.5) = 1.35.

1.35 x 10" (height) = 13.5 (radius)
13.5 x 2 = 27" diameter.

This ignores the refraction of the water, reflection of the glass, etc. Which would take someone smarter than me to figure out.

oreo54 · Mar 14, 2022

piranhaman00 said:
That would be at the surface of the water correct? What about 10” down? Can you show the math;)

https://store.marinebeam.com/beam-angle-calculator-1/
Includes what goes into rating a lens..

Anything past the water surface is complicated by refraction/reflections of the water/glass.

Like BRS does, you just need to minimize spill.
One exception is if you have no way of controlling PAR by dimming and can only raise/lower light to compensate.

10" down the "math" is complicated..
Same with overlapping "cones" with multiple lights at the surface.