Photographers working with historical processes use a variety of artificial light sources when printing, many of which emit ultraviolet (UV) light. Exposing the print to a precise amount of light energy is critical for successful printing. Most often this control is achieved by measuring time: switch on the light source, start a clock, and then switch off the light source when the desired time has passed.
This is good enough for most purposes, but it is not ideal because the amount of light emitted by all light sources varies over time. This is common when light sources are warming up, but it may also happen in other circumstances such as if the electrical supply is unstable.
The chart below shows the change in power output over time for a typical ultraviolet (UV) fluorescent tube light source. The chart shows that when switched on, the UV light produced by these tubes is a little bit less than two thirds of peak output. It takes about two minutes to reach a steady state output, but even then, the power continues to fluctuate.
When printing with time-based exposures, the photographer cannot help but ask, “Was this three-minute exposure the same as my last three-minute exposure?”
For the ultimate in control, it is better to base exposure upon the total amount of light produced by the light source, rather than elapsed time. A properly calibrated light integrator allows the printer to do this with ease.
A light integrator continually monitors the intensity of light from the light source. It allows the printer to make exposures based upon the total amount of light emitted, rather than the amount of time that has passed. Fluctuations in the light intensity are thereby factored into the overall exposure. If the intensity dips, then the exposure time automatically increases to allow for this; and if the intensity rises, then the exposure time automatically decreases.
Up until now, fully functional light integrators have been prohibitively expensive; the preserve of professional printers who can afford thousands of dollars of capital equipment. But no longer – the Light Counter LC2 light integrator system bring this control within reach of all photographers.
Got a question? If so then just send me an email using the address at the bottom of this page, or leave a comment. I will reply as quickly as I am able.