Abstract: A light source for providing controllable illumination having the red, green, and blue components in selected intensity proportion, uses a lamp/filter assembly which projects light through a diffusing plate into a mixing chamber from the output end of which mixed light is emitted for illuminating photographic paper through a negative. The chamber is rectilinear, and the red and green lamps project toward opposite corners while the blue lamp projects along the axis of the chamber. A light pipe which has an input end facing the output end of the chamber extends into the chamber and extracts light which is processed in red, green, and blue channels having temperature stabilized phototransducer circuitry and control circuitry wherein signals corresponding to the intensity of the color components are processed in the channels and are modified by control signals which can be produced in the photo printer control computer.

Abstract: A method and apparatus for regulating the RMS voltage applied to a load from an AC source having a peak-to-peak amplitude which varies within a predefined range. The apparatus comprises a waveform generator for producing a predefined periodic waveform, a comparator circuit for comparing such waveform with the sinusoidal waveform of the source whereby a signal is produced each time the algebraic difference between the instantaneous values of the compared waveforms changes sign, and a switching circuit responsive to the comparator circuit output for interrupting the voltage applied to the load at the start of each cycle or half-cycle. The shape of the waveform produced by the waveform generator is such that the desired RMS voltage appearing at the output terminals is produced.

Abstract: An r.m.s. voltage regulating circuit for maintaining substantially constant the r.m.s. output voltage of an A.C. source. The circuit preferably includes a triac and a timing circuit for controlling the non-conduction angle thereof, preferably at the beginning of each half cycle. A function generator compensates for the non-linearity in the relationship between the r.m.s. value of the output voltage and the amplitude of the A.C. voltage source.