Characteristics of some dimming system are described.
(1) Dimming by voltage reduction
Light output of fluorescent lamps is controlled by means of variations in line voltage. It is simplest method, but the dimming characteristics are not very excellent.
(2) Dimming by transductor.
Brightness of fluorescent lamps can be controlled in the range of 100 to 1 by this system. It is most useful in future.
(3) Dimming by resonance circuit
Brightness of fluorescent lamps can he dimmed to about 5 percent of normal brightness by the resonance circuit of reactor and capacitor, of which values are selected carefully.

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Colors of the high-pressure mercury-vapor lamp (HL), the super-high-pressure mercury-vapor lamp (SHL), and the color-corrected mercury lamp (FHL) should be named from the colorimetric data greenish white, yellow-toned-greenish white, and yellow-greenish white, respectively. As regards the subjective appearances, however, they change from white to quite saturated green by the observing conditions. These phenomena can be solved by the knowledge of physiological or psychological effects of the eye, especially of glare and small field tritanopia.
Color rendering properties of these lamps and the mixture of these lamps with the incandescent lamps (1L) are evaluated according to Azuma-Mori method. Consequently, it is proved that the color rendition by FHL nearly equals that by the mixture of HL and IL in luminous ratio of 8: 2. If mixture lighting of mercury and incandescent lamps is wanted for desirable color rendition, luminous ratio of 5: 5 for HL and IL mixture or 7: 3 for FHL and IL mixture is recommended, in view of not only color renditions but average color temperatures and luminous efficiencies. The color rendition by these mixtures is as preferable as by standard type fluorescent lamps.

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