What is an exposure Unit?
An exposure unit is used to burn artwork into a screen using ultra-violet light. The screen exposure process revolves around taking artwork printed on a film positive, taping it to the print side of the screen, placing it on top of the glass portion of the equipment, and then turning on the light that exposes/burns the artwork into the screen. Once the exposure process is complete, the artwork must be washed out of the screen using water to create the end stencil that will be used for printing. A good way to think about it is that it is a big light box filled with light bulbs. The quality of the exposure unit is one of several variables that will affect the success or failure of exposing a screen. While the unit itself is important to be high quality, it is also very important that you are working in a light safe area, you are using the right emulsion, the exposure times for different mesh screens is dialed in, and the film positive is very opaque. If any of these variables are less than ideal, then you might have problems and need to know which one needs to be fixed to solve the problem.
How to Select the Right Exposure Unit
There are many manufactures of exposure units, and thus several on the market to choose from. When selecting an exposure unit to purchase it is very important that you buy something that will deliver the results you need. The first factor to think about when selecting an exposure unit is the largest potential screen you might have to burn. Most exposure units are built with a hinged top typically made some type of rubber material that sits on top of the screen while it is being burned and typically contain a vacuum. The top is made up of rubber material and contains a vacuum so that the screen can be compressed as much as possible to prevent light slipping in between the film and the screen, which leads to problems. So any screen that is smaller than the glass top area should have no problems with being exposed as it is not like the screen has to sit in a jig of any kind.
The second primary factor to consider is how detailed of artwork you plan on printing. The more detailed the artwork is the higher mesh screen will be used and potentially halftone dots for process printing. In order to hold all of the detail in a high mesh screen, you must have a high quality exposure unit that can deliver the perfect amount of light to burn the artwork into the screen. The last factor to think about is the actual type of bulb that is being used within the unit. Most exposure units are now built using LED bulbs, which last a lot longer and thus don’t have to be replaced as often as often as old school halogen bulbs. However, not every LED bulb is the same. LED bulbs can come in strips that look nothing like a bulb. The type of LED bulb can often determine the success of exposing higher mesh screens with a lot of detail.