Enter a light source's total luminous flux and beam angle to calculate its luminous intensity in candela.
How to Use the Lumens to Candela Calculator
Enter the lumens figure from the bulb's packaging into Luminous Flux, then set Beam Angle to the fixture's published beam spread — the calculator returns the equivalent candela rating instantly.
A light bulb's box lists lumens. A spotlight's spec sheet lists candela. Comparing the two numbers directly is meaningless until one gets converted into the other, since candela measures how concentrated the flux is in a given direction rather than how much of it exists in total.
solid angle (sr) = 2π × (1 − cos(θ ÷ 2))
candela = lumens ÷ solid angleθ is the full beam angle in degrees. Narrow that angle at a fixed lumen output and candela climbs, because the same total light is now concentrated into a smaller solid angle — which is exactly how a flashlight's reflector takes a small, unremarkable bulb and turns it into something that reads as intensely bright in one direction. Widen the beam and the opposite happens: more coverage, lower candela, for the same lumens.
Push 800 lm through a tight 20° beam and candela climbs above 8,300. Spread that identical 800 lm across a wide 120° beam instead and it falls to roughly 255 cd — same bulb, same total light output, wildly different intensity numbers depending entirely on the reflector or lens sitting in front of it.
This is also why two bulbs with identical lumens ratings can post completely different beam-intensity numbers on a comparison chart. The missing variable is never the bulb's total output — it's how tightly the reflector or lens focuses it.