The CX Mazda lamp is a 115-volt 500-watt tungsten filament housed in a Corex-D glass bulb of 1 mm. thickness, which has been frosted on the inside and which transmits light waves down to 2,800 angstrom units. The color temperature of the filament is 3035° K, the designed life of the lamp is 500 hours, and its luminous efficiency is 21.5 lumens per watt. Its spectrum is continuous and in this respect is like that of sunlight. Its spectral energy distribution, however, is somewhat dissimilar in that its maximum energy output is more in the infra-red part (fig. 1). The energy emitted in wavelengths from 2,800 to 3,200 angstroms, i. e., the antirachitic regions, is only 0.023 per cent of the total or 0.1 watt of the total 500 watts and represents an average daily amount, as used by us in this study, which is equivalent to approximately one seventh