Grafica News - Aug 2015
Grafica participates in SPAI's Cross Country Table Top Exhibitions : Pune/Solapur
All types of exposure lamps lose UV intensity or level of actinic light as they age. While a lamp may seem bright, UV light output needed for exposure cannot be seen with the human eye. UV intensity will steadily decline and eventually lose the ability to adequately expose the stencil.
The best option to address these progressive changes is to use a light integrator for exposure instead of a timer. Light integrators measure the quantity of UV light reaching the screen using a photocell, and automatically adjust the exposure length to ensure the light dose is the same each time[Figure 1]. This effectively compensates for lamp decline and minor voltage fluctuations.
Integrators use 'units' of light instead of minutes and seconds (although most integrator controllers allow you to set actual time if you wish.) Initially when a new lamp is installed the integrator photocell is calibrated so 60 units equals approximately 60 seconds of time at a specified distance. This provides an easily understood unit equivalent for entering/determining exposure times.
Figures 2 & 3 Figure 4 To actually quantify the intensity and quantity of UV light arriving at the exposure surface, an integrating radiometer is needed. A radiometer is a portable device designed to provide independent readings of UV light emissions through the use of a photo sensor. There are two main configurations offered, self-contained designs and types including a remote photo sensor attached with a wire .