LED Lens solutions

[Hdhuntr01]

There is a ton of information about LEDs out there but I find little on lenses. What I am trying to calculate is:

A CREE XP-G with an 80 degree lense at an elevation of 12" will produce a coverage of XX inch diameter. What does XX equal? How do I determine the spread of any particular lens at any certain height?

Soooooo confused...

 

[nstiesi]

Its a geometry problem. Construct a right triangle. The base is 1/2 the diameter of the light spread. The height is the distance from sand bed to LED. If you solve that triangle for the angle between the height and hypotenuse, you get 1/2 of the lensing angle. So in your case, you know 1/2 lens angle = 40 degrees, and elevation is 12 inches. so tangent(40) = XX/12. Solving gives XX = 10", so your diameter is 20"

 

[nstiesi]

Something to remember, the way optics are rated, is that the angle given (i.e. an 80 degree lens/reflector) is the angle at which the intensity of the light drops to some % of its max value. So, lets say a light with that optic on it measures 100 lux (which is a measure of intensity, so its lumens per unit area, in english units its called footcandles) directly under the light at a given distance, the lux measurement 40 degrees from bottom dead center on either side is 50 lux. There will still be light that falls outside of that cone, its just below 50% intensity.

 

[Hdhuntr01]

Thank you. This is exactly the equation I was seeking. I knew there was one out there just didn't know what it is. Really appreciate the info.

 

[radicaltimes]

Go to reefledlights.com then to their light my tank page. There will be what you need . 60 degree are good for 12" above the tank and 80 are real good for around 8"above it