Lens Degree and mounting height

[piranhaman00]

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]

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

 

[jdmee]

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.

beam angle - Illuminating Engineering Society

[8.6.4.1] The angle between the two directions for which the intensity is 50% of the maximum intensity as measured in a plane through the nominal beam centerline. For beams that […]

www.ies.org

 

[piranhaman00]

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.

beam angle - Illuminating Engineering Society

[8.6.4.1] The angle between the two directions for which the intensity is 50% of the maximum intensity as measured in a plane through the nominal beam centerline. For beams that […]

www.ies.org

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

 

[jdmee]

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]

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

LED Lighting Beam Angle Calculator

A simple calculator that determines spot size by a light's beam angle

store.marinebeam.com

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.

 

[oreo54]

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

That's what par meters are for..

Index of refraction gives you an estimate till it hits the glass.