Xenon projector lamp

A xenon short-arc lamp makes light by passing a current through xenon gas held at high pressure between two electrodes. It replaced the carbon arc in film projection and carried over into the first generation of digital projectors. Many cinemas have since replaced lamp projectors with laser light sources, compared on the laser projection page, but lamp projectors are still in service.

Lamps are sold by wattage to match the projector and screen. Ushio's xenon short-arc catalogue, for example, runs from 75 W to 7,500 W, with average rated life between 200 and 3,000 hours depending on the model and burning position. Brightness falls as a lamp ages, which is one reason to measure the screen in foot-lamberts rather than trust the lamp-hour counter.

The same brochure is blunt: lamps used past their rated service life are more likely to break and burst because the glass deteriorates. Running a lamp beyond its hours saves the price of a lamp and risks the projector's optics and a cancelled show.

Spent lamps still hold pressure and must be made safe before disposal. Ushio's procedure is to break the glass inside a protective wrap or case, wearing the same protective gear, and dispose of the remains as industrial waste. Check local rules too.

The lamp also shapes the booth. UNIC's cinema design handbook notes that medium and large xenon projectors need external exhaust ducting of around 800–1,000 m³ per hour; see projection booth. When lamp cost, downtime and ducting are added up, the case for laser often makes itself, as covered in the cinema projector buying guide.