Light-bulb packaging in the US lists lumens — 800 lumens for a 60-watt-equivalent LED — but lighting engineers talk about candela, the SI unit of luminous intensity. The relationship is beautifully simple: one candela equals one lumen per steradian, meaning a 1-candela source radiates one lumen into each unit of solid angle. An ordinary candle is roughly 1 candela, which is where the name comes from. Flashlight makers love candela because it captures beam intensity: a tight-beam flashlight can hit thousands of candela from modest lumens, which is why "throw" specs use it.

Type your value in the Candela (cd) box and the Lumen/steradian (lm/sr) readout mirrors it exactly — 1 to 1, the cleanest factor on this page. The Hefnerkerze (hk) column is the historical curiosity: an old German standard candle, where 1 cd equals about 1.107 hk, still cited in vintage optics literature. The 100-candela example gives 100 lm/sr and about 110.7 hk. Stage-lighting designers, automotive engineers aiming headlights to DOT standards, and photographers comparing strobe specs all work in candela when direction matters — lumens tell you total light, candela tells you how intense the beam is where it lands. Remember the pair: lumens measure total output, candela measures intensity in a direction.

With the pre-filled defaults — Candela (cd) 100 — the Luminous Intensity Converter returns Hefnerkerze (hk) 110.7000, Lumen/steradian (lm/sr) 100.00. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.