Printer's Resource FAQ

What is the difference between Metal Halide, Mercury Vapor, and Quartz Halogen light sources?

Metal Halide and Mercury Vapor are two similar types of gas discharge lamps that output light in two different areas of the UV spectrum. Both lamps create light by heating up metal additives. Most of today’s emulsions perform best under the spectral output of the metal halide, so it has become the most popular light source. In fact, some modern metal halide lamps are multi-spectrum lamps. Their specialized metal additives cover a wider spectrum in order to match a broader range of emulsions.

Although Quartz Halogen lamps have been used for screen making, they produce a very poor light source. The quartz halogen lamp is basically a high-wattage incandescent lamp that emits a lot of white light but very little of the UV that emulsions require. It's ironic, but some people invest in what they think is a high-quality exposure system and then compromise performance by using the wrong light source.

Metal Halide is the best light source for today’s emulsions, but be aware that not all metal halide lamps are the same. Those designed to light a warehouse or parking lot have additives that give off more visible light. The light source that provides the best results and fastest screen exposures peaks out in the 350-450 nm range.