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FLOFormlight Optics

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LED beam angle calculator

Relate a round spot on a flat target to the full angle of the beam, or run the same geometry in reverse. An optional estimate turns intensity or flux into on-axis illuminance.

Calculate

Distance along the beam axis to a flat target.

Diameter where intensity is half of the peak. This does not convert to a field angle.

Angle meaning

Beam angle is the full width at half the peak intensity (FWHM). Field angle is the full width at 10% of the peak. The geometry uses the contour you measured. It does not convert one into the other.

Optional. Leave this out if you only need the angle or the spot size.

Result

Full beam angle (FWHM)

53.1301°

Half-angle 26.5651°.

θ = 2 arctan(D / (2 L)), with D and L in the same units.

Assumes a round spot on a plane normal to the beam, and this angle is the full width at half the peak (FWHM), not the 10% field angle.

A published beam-angle lens family for a clustered LED downlight is in the portfolio. For a source that may not fit the receiver, use the etendue calculator.

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Fixed-fee projects. Scope, deliverables, and price are agreed in writing before work starts.

Get a fixed-fee design quote.