Beam Lux
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Lux, candela, and beam diameter

Enter lumens, the full beam angle, and the distance. Illuminance and beam diameter are shown first.

Theta is the full beam angle, not the half angle. Use the slider or type the distance and angle.

Worked example

beam angle 36°distance 2 mbeam diameter

Illuminance812.9527 lx

E_lux = I / d^2

Beam diameter1.2997 m

D = 2 × d × tan(theta / 2)

These formulas assume the flux is spread evenly inside the cone. A real lamp does not have that ideal distribution.

Solid angle, candela, and throw

Solid angle 0.3075 sr

Omega = 2 × pi × (1 - cos(theta / 2))

Luminous intensity 3251.8107 cd

I = Phi / Omega

Foot-candles 75.5251 fc

E_fc = E_lux / 10.764

Throw to 0.25 lux 114.0493 m

d_throw = 2 × sqrt(I)

Notes only: hallways and stairs 100 lux; office and classroom 300 to 500; drafting 750 to 1000; operating theater 10000 to 50000.

Theta is converted from degrees to radians for cos and tan. The feet form is not applied as a second conversion.

Worked examples

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