Quantum - smallest indivisible unit of radiant energy.
Quarter Wave Plate - a optical element used to convert polarization in between circular and linear.
Quarterplate - negative or print format measuring 3 * x 4 * inches. It's one quarter the size of a full plate (8 * x 6 * inches).
Quartz-iodine lamp - compact tungsten filament lamp designed to maintain its color temperature and light intensity throughout its working life.