showstack / glossary / beam-angle
Beam angle / field angle 光束角／場角
Two different measurements of how wide a light source spreads. Beam angle is where intensity has fallen to 50 percent of centre; field angle is where it has fallen to 10 percent. A fixture quoted at one number and compared against the other will look wrong on paper and on stage.
中文
描述光源擴散寬度的兩種不同量測。光束角是強度衰減至中心 50% 之處，場角則是衰減至 10% 之處。以其中一個數字標示的燈具，若拿去和另一個定義比較，紙上與台上都會對不起來。
Regional usage
| Where | Term | Note |
|---|---|---|
| UK / US | Beam angle / field angle | |
| HK / TW | 光束角 / 場角 |
Easy to get wrong
Field angle is always the larger number. A data sheet quoting a single "beam" figure is usually quoting the 50 percent one, which makes the fixture look tighter than it looks in a room.
Next to this
Moving head搖頭燈A fixture whose whole optical head pans and tilts on motorised yokes, as opposed to a fixed fixture or a mirr…Focus對燈Pointing and shaping each lighting fixture: where the beam lands, how hard the edge is, what it has to miss. …
Sources
- ANSI E1.9 reporting photometric performance data — ESTA TSP primary
- Theatrecrafts glossary of technical theatre terms — Theatrecrafts / ABTT heritage primary
Understand the mechanism
Something wrong, or missing?
Every entry here is maintained by people who run shows.
Edit this entry on GitHub — one file, editable in your browser, and your handle goes on it permanently.