Guess you caught me napping on this one. I will not try to go back over all that has been said, but will give a few comments on the integrator and light source.
Concerning the integrator, much like a measuring cup, it is looking for a quantity of light and when the specified amount is seen it shuts the light off. This allows the unit to adjust for the aging of the lamp and also for changes in line voltage coming into the unit. There is a photo cell that looks at the light and sends a small amount of voltage to the integrator. In order to get the most accurate exposures, the lamps are made to output a specific nanometer range to match the emulsion. We put different filters in front of the photo cell depending on what lamp is being used so that we are not just looking at the quantity of light, but the quantity of light within the range of light that the emulsion needs. We all use the term "units of light", and as most of you know that is more of a number than a quantity. Honestly, it does not matter if you are exposing for 20 units or 120 units as long as you are getting the correct exposure and it is consistent. When we set up a unit in the factory, we set up it up so that 30 units is approximately 30 seconds. This gives a good starting point to work from. If you are dealing with a unit that has been in use for a period of time, then it will slowly take longer to reach the same amount of light as when the lamp was new. Other things that can effect it are the voltage tap settings and the age of the lamp. If you are dealing with an older unit and not sure where to start with your exposure tests, try setting the integrator at 60 units and time it to get an idea of the units to time relationship. Then you can usually get a starting point from the emulsion manufacturer for testing.
I will agree with some of the comments about the effect of time and light. In addition to having a good vacuum, the most important thing is to use a lamp that outputs most of its energy within the proper nanometer range. That way most of the light energy is being used for exposing the emulsion. If the lamp is not a good match, then it takes much longer for the correct quantity of light to effect the emulsion and this is when you get unwanted effects by having the wrong wave length working on the emulsion for an extra long period of time. The wattage of the lamp also plays in here. Larger units with the ability to expose multiple or larger screens, require that the lamp to screen distance be increased to get even coverage. As this is done, a more powerful lamp is needed and the wattage is normally increased to compensate for the difference and the fact that these shops are probably making more screens and desire faster exposure times.
Ron Hopkins
NuArc Sales Mgr.
M&R Sales and Service
