At American Screen Printing Association, we get lots of inquiries about using LED light from people who are building their own exposure units.
Since traditional 'high UV' light sources (metal halide and mercury vapor lamps) for 'home made' exposure units are becoming harder to find, LED lights sources are available that are affordable, safe to use and will work effectively for exposing screens.
Before we discuss LED light sources, we need to discuss some important details regarding light sources in general when building your own exposure unit.
The ideal light for screen exposures is one that is rich in ultra-violet (UV) light. Fluorescent, halogen lights and most LED lights are low in ultra-violet (UV) light. But they have a low purchase price and are readily available. This is why most low cost exposure units have them as a light source. On the other hand, a light source high in UV, e.g. metal halide or mercury vapor lamps are more costly, not as easy to source, and more difficult to implement into a typical home-made exposure unit. As a result, you don't see them used as often.
As we have written in a previous article on light sources for exposure units, most people who want to build their own exposure unit mistakenly think that the light source is the most important consideration. It isn't. While the light source will determine what kind of art you can use to make a stencil, the type of emulsion or capillary film that you use is actually more important. If you think of emulsion (or capillary film) as the 'photographic film' used to make your stencil, think in terms of speed and light sensitivity.
Photopolymer emulsion is very sensitive to light. It exposes very quickly and has a wide exposure time range. Manufacturers developed photopolymer emulsion products because they know that many screen printers use an exposure light source that is less than ideal. Photopolymer liquid emulsions (and photopolymer capillary film) work well even with poor light sources. Using a photopolymer emulsion (compared to a diazo-based emulsion) when you have a low UV light source will make a huge difference toward success or failure when making a stencil.
LED lights are becoming more and more popular and are becoming the lighting standard in USA. As prices are becoming par with fluorescent lamps, LED lights are becoming more widely available.
For exposing exposing screens, LED lights have several distinct advantages:
LED light sources that have a high lumen output work best for exposing screens. Assuming you are using a photopolymer emulsion, high output LED lights should work well as a light source when you are building your exposure unit.
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