How important is the distance of my UV light source from my substrate?

The output power of your light source does not change with distance, but "Irradiance" or how much energy your substrate sees, does change.

Shine your flashlight on the wall in front of you and move it away from the wall, and you will see the intensity of the light drop. The irradiated area grows but becomes less intense. This is essentially de-focusing and or reducing the intensity of the available light at the surface you are illuminating. (The power output of the flashlight didn't change, how you chose to use the available light is what changed)

How reactive your UV curable adhesive, coating, ink, or whatever it is you are curing will be a factor in how much power you need to complete the cure within your desired processing time. Some UV light sources have a fixed output, and the only way you can change the power that's delivered to your substrate is to move the light closer to increase irradiance, or move it further away to decrease irradiance. Some UV light sources have variable power supplies allowing you to change the irradiance value the same way a dimmer switch works.

If you are using a special fill bulb, or "doped" bulb such as a bulb with iron in it to produce more long wavelength UV, lowering the output power of the light source can cause a wavelength shift, so be aware of this potential and consult with your light source and chemistry experts to be sure you have considered this when developing your process.

All UV light sources will have a characteristic focus or distance where the light produces the most energy. Knowing this distance will help you select the appropriate power lamp for the chemistry you intend to cure, and help you determine the speed you will be able to run your process. Pay close attention to the distance of your light source to your substrate, as energy from UV light sources drops significantly with even small changes in distance!

Ask TTG for more information on the specifics of power and distance for your light source!