=Gas-filled Lamps.=--Until 1913 the filaments of all Mazda lamps operated in a vacuum. The vacuum serving the purpose of preventing oxidation and at the same time it reduced the energy loss to the least amount. It was found, however, under some conditions of construction that lamps filled with inert gas gave a higher efficiency and more satisfactory service than those of the vacuum type. In this construction, the filament is operated at a temperature much higher than that of the vacuum lamp and as a consequence gives light at a less cost per candlepower. Mazda vacuum lamps are now designated by the General Electric Co. as Mazda B lamps, Fig. 224, and those of the gas-filled variety, Fig. 225, are designated as Mazda C lamps. [Illustration: FIG. 224.--40-watt Mazda B lamp (1/2 scale).] [Illustration: FIG. 225.--750-watt Mazda C lamp (1/4 scale).] The filaments of the gas-filled lamps are intensely brilliant and where they come within the line of vision should be screened from the eyes. The high efficiency of these lamps permit the use of opal shades to produce a desired illumination at a rate of cost that compares favorably with the unscreened light of the vacuum lamps. =Daylight Lamps.=--The color of the light from an incandescent electric lamp depends on the temperature of the filament. In the case of the gas-filled Mazda lamp the high filament temperature produces a light that differs markedly from the vacuum lamps in that it contains a greater amount of blue and green rays. It is therefore possible to produce light that is the same as average daylight. Gas-filled lamps with globes colored to produce light of noonday quality are produced at an expenditure of 1.2 watts per candlepower. In the matching of colors, it should be kept in mind that the tint of any color is influenced by the kind of light by which it is viewed. Colors matched by ordinary incandescent light containing a large percentage of red rays cannot produce the same effect when the same articles are seen in light of different quality. The daylight lamps are therefore intended to be used under conditions that require daylight quality.