The quantum efficiencies of CRT and FL tubes that use a phosphor screen as transducer of invisible particles to light in visible spectrum wavelengths were calculated in this study. The phosphor screens in CRT tubes have quantum efficiencies greater than 3,000, which give the luminance of comfortable images on phosphor devices for the observation by the eyes. The established FL tubes have the amazing quantum efficiency of $3{ imes}10^{10}$ photons per moving electron per FL tube, which allows the illumination of a $5{ imes}5;m^2$ room by three FL tubes, with heating at $40^{circ}C$. Thus, FL tubes, including for backlighting of LCD displays, have a superior over other illumination sources.