Screen Exposure Units – Everything You Need To Know

Screen Exposure Units: Everything You Need To Know

A good screen exposure unit is an essential part of every screen printing business. Since setting up a new screen printing business or indeed investing in new equipment for an existing t-shirt printing business is expensive, it is therefore crucial that you invest in equipment that will help your business to grow and operate as cost-effectively as possible. A good choice of equipment will do that, while a poor choice will likely achieve the opposite and cost you more in the long run.

If you want to produce great looking screen printed t-shirts and other products, you have to use a screen exposure unit that is capable of exposing high quality artwork and ultimately produce high quality screens. With a variety of units available, there are some upfront considerations and decisions. If you need any further help and advice, please feel free to contact us.

Review the video below that covers “Everything you need to know about: Screen exposure units

1. How do LED screen exposure units compare with metal halide for exposure speed?

The Vastex range of LED screen exposure units that we supply are comparable in exposure speed to a metal halide unit of 5 kW power. The benefit of LED is of course that it consumes dramatically less energy and offers much longer bulb life, leading to much reduced running costs.

2. How often do I need to replace the lights on my screen exposure unit?

  • UV Fluorescent tubes should be replaced roughly once a year. Always replace all tubes as a set rather than individual lights.
  • Metal halide bulbs should be replaced every 3 – 6 months depending on use.
  • LED lights can last for in excess of 50,000 hours of use. Vastex LED lights are under warranty for 3 years.

Metal Halide Screen Exposure UnitMetal halide bulbs are significantly weaker after only 700 hours of use and the use of a light integrator is important to continue adjusting exposure times automatically as the bulbs weaken over time. Without a light integrator to continually monitor and adjust the exposure times on your metal halide screen exposure unit, regular use of an exposure calculator would be imperative to ensure accurate exposure times.

Keep in mind that although your metal halide screen exposure unit will continue to put out light, this is not an indicator that it is still working effectively.

We highly recommend that if you have a UV fluorescent or metal halide screen exposure unit, you keep a spare set of lights on-hand to avoid downtime.

3. How do the different types of screen exposure units compare on loss of detail?

Multi-source light units will have undercutting and drop the finest of details, while a single point light source such as metal halide preserve more of the finest detail.

  • Vastex UV Fluorescent tubes will suffer a loss of roughly 15 – 17%
  • Vastex LED screen exposure units will suffer a loss of 7 – 9%
  • Metal halide exposure units will lose 2 – 5%

4. What is a vacuum bed exposure unit and why do I need one?

Screen exposure unit with vacuumIn order to create good quality screens from highly detailed artwork, it is always recommended that a vacuum bed screen exposure unit is used. Unlike more basic pressure based uv exposure units that use foam pressure pads or weights to hold the artwork against the screen during exposure, a vacuum bed uses a vacuum pump to pull the artwork tightly together with the screen (or other product being exposed) against a sheet of glass, creating a very close contact during exposure.

Without a vacuum system, the contact between artwork and screen emulsion will be less than optimal and fine definition will be lost. A vacuum bed screen exposure unit is an absolute must for reproducing halftones and highly detailed designs.

5. How does a pressure pad exposure unit work and what applications is it used for?

Pressure pad screen exposure units use foam pressure pads and weights to hold the artwork against the screen during exposure. This method is a much more basic approach than using an exposure unit that utilises vacuum. The contact between the artwork and the screen or other substrate will never be as good, so pressure pad exposure units are best for use with artwork that does not contain a great level of detail. If your artwork contains halftones, this type of unit is not suitable.

6. Are home-made exposure units an option?

If you only print as a hobby, such units may be viable but there are many pitfalls in using a home-made system. The biggest benefit is that they are cheap. An inexpensive halogen work light on a stand is all that is needed, along with something to hold your artwork and screen together during exposure. Halogen lights generate a lot of heat and is extremely inefficient, which means your screen exposure times will be very long indeed. It is therefore not something a business would or should use.

Master screen printer Douglas Grigar explains more about home made screen exposure units in the video below.

7. Is the light from exposure units harmful to the eyes?

All uv light is harmful to the eyes, but the level of danger varies according to the type of light produced. The tubes used in the Vastex fluorescent UV units do not produce the dangerous spectrum of uv light, but, it is advised not to run the unit without the lid being closed. The same is true for the LED models.