Since an LED emits light roughly in the shape of a cone, we can use triangle math to predict the amount of area an LED in a particular installation will light up.

After the calculator has any three parts (not only the ones I entered) of the triangle, it will calculate the rest of the parts.

In the calculator pictured, I’ve entered the three values that are depicted in green – the calculator figured out the rest.

For this example, I know:

I have 90° lenses

I have to cover a 20″+ diameter of surface area

I need to know how high to mount the fixture to get 20″ in diameter of coverage.

Here’s how I filled out the calculator:

Divide the 90º lens by two to get angle 1: 90° / 2 = 45°

The light is perpendicular to the water, so angle 2 is 90°

Divide the diameter by two for the radius you need to cover, for side 1: 20″ / 2 = 10“

From this, the calculator tells us (side 2) that the light should be mounted 10″ above the water.

Here’s a simple diagram I created based on some similar calculations: