Learn ways to increase your production while reducing cost, heat, and wasted energy.
Equipment manufacturers can theoretically pack lots of elements together to get a very high watt density, but with bulbs costing more than $80 each, it makes sense to use as few as possible to get the job done. (Not to mention that energy costs would be doubled with such a design and the life of the bulbs could potentially be shortened due to the close proximity of the lamps to one other.) As with most things in screen printing, the challenge comes down to balancing cost and effectiveness.
To improve the efficiency of the bulbs, manufacturers commonly back them with parabolic reflectors that help focus the energy evenly across the printing platen. In order to get maximum uniformity and heat distribution, each manufacturer has designed their reflectors based on the target watt density of their flash unit. (See Figure 4.) Each design has a specific focal distance. If you set your lamps higher, you will still get even heat, but the intensity will drop off quickly and your flash times will skyrocket. If you set them too close, the surface temperature will be very uneven and you will have heat banding in areas where the energy is being concentrated.
How far should you set the panel or lamp head from the print surface and what happens when you change this distance? This is a very important question, because small changes can make enormous differences in surface temperature.
Energy drop-off follows the inverse square law, the same formula used in screenrooms to calculate changes in exposure as the light source is moved closer to or farther away from the emulsion. Shops with fixed-distance LED exposure units no longer need this calculation to burn their screens, but for calculating surface energy, it is still very important.
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