Beam Angle Calculator

Photometry · Beam

Know the pool size you want and how far the fixture sits? Find the beam angle — the optic — you need to buy. Adjust the sliders and the diagram shows the matching cone.

θ = 2 × arctan( D / (2 × d) )  ·  D = desired pool diameter, d = distance
Presets:




Match the angle to a standard optic
Optic Beam angle Typical use
Narrow spot (NSP) 8–15° Artwork, columns, signage
Spot (SP) 16–24° Retail display, accents
Flood (NFL/MFL) 25–40° General accent, dining
Wide flood (WFL) 45–60° Ambient fill, wall wash
Very wide (VWFL) 70°+ Low ceilings, even fill

Already know your beam angle and want the spread instead? Use the Beam Spread Calculator.

Worked example: to light a 1.2 m pool from 2.4 m away you need 2 × arctan(1.2 / 4.8) = 28° — a spot / narrow-flood optic.

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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.