Screen printing exposure units have used a variety of light sources — UV, halogen, metal halides, etc. LED bulbs have now become the standard light source for exposure units. Why the shift? LED bulbs have many advantages due to their wavelength and energy usage. 
purple led lights on with a screen sitting on the exposure unit glass


With any exposure unit, the goal is to have a light source that penetrates the emulsion coating and promotes crosslinking. Lights using the correct wavelengths will positively affect exposure times and proper emulsion cure.
The wavelength of light affects how well light penetrates and crosslinks emulsion. Crosslinking the emulsion with the mesh is important because it produces a robust screen that can withstand the rigor of printing and cleaning on the press. A 405 nm light source has the right wavelengths to cure the entire emulsion surface as well as its layers, which helps the emulsion crosslink with the mesh. But, there’s a way to achieve a better screen. A 405 nm LED light source has a wider exposure latitude, meaning it cures the front, middle, and back of the coating at the same time, resulting in deeper light penetration. The result is an even stronger, more durable screen.
a burned screen that says elevate your darkroom


As stated earlier, LED bulbs have optimal wavelengths, which enhance a screen’s durability. That’s not the only benefit of LED bulbs. They also burn screens faster, capture more detail, and last longer on press. With an LED exposure unit, printers are able to reproduce high-quality burns every time. 
a screen on an exposure unit with its inspection lights on.


An added bonus of LED bulbs is their energy efficiency. Halogen bulbs use about 5x the amount of energy that an LED bulb uses. LED bulbs also use electricity better: 95% of the energy used is for producing light, while only 5% is wasted. Since halogen bulbs rely on heat to produce light, 90% of their energy is wasted. 
On top of energy usage, LEDs have a lifespan of 10,000 hours (the lifespan of a halogen bulb is about 50,000 hours). Halogen bulbs are ineffective. With LED, printers save time, money, and energy.
Printers that do not have an LED exposure unit in their darkroom should plan to upgrade their equipment in the near future. It produces better results while saving time and money. That’s music to a screen printer’s ears.