all original c. 1930's vintage industrial new old stock mazda c 1000 watt "projection" light bulb or lamp. the mazda brand lamp was manufactured by the westinghouse company. contains a "mogul" threaded base. the packaging contains graphics, specifications, etc., is original and in great condition, considering age. excellent working condition. the mazda "c" lamp resulted from the discovery by dr. irving langmuier that the rate of disintegration or evaporation of the incandescent tungsten filament could be materially reduced by operating it in an atmosphere of chemically inert gas instead of in a vacuum. this discovery was of great importance, as the useful life of a tungsten lamp is determined by the rate at which the filament disintegrates. in the first place the disintegration progresses in time to such an extent that the filament fails, and in the second place the metallic tungsten thrown off from the filament is deposited on the bulb and the deposit eventually becomes so dense that the light output from the lamp is seriously reduced. prior to dr. langmuir's discovery much had been accomplished in the vacuum type of lamp by the use of chemicals known as "getters," which combined with the deposit and changed its color to white or yellowish-white and so reduced the amount of light absorbed. it seemed, however, that the limit had been reached in lamps which operated at an efficiency of about 11 lumens per watt, and the prospects of attaining higher efficiencies with a tungsten filament operating in a vacuum did not seem very promising. the lamp engineers, therefore, foreseeing the possibility of further increasing the efficiency of the tungsten filament lamp by operating the filament in an atmosphere of inert gas instead of in a vacuum, devoted their attention to the production of commercial lamps of the gas-filled type. after much experimental work a satisfactory type of construction was developed, and in the early part of 1914 several sizes of street series lamps and the 750 watt and 1000 watt multiple lamps were placed on the market. in developing these lamps many problems not hitherto encountered in lamp design had to be solved. the most important of these was to reduce the energy losses caused by the presence of the gas in the bulb, and this was accomplished by winding the filament in the form of a helical coil, thus reducing the area exposed to the cooling action of the gas and making the bulb as small as possible and so reducing the radiating surface. since there were now two types of mazda lamps it became necessary to distinguish between them, and the names mazda "b," to describe the vacuum type, and mazda "c," to describe the non-vacuum, or gas-filled type, were adopted. in the course of the development of the mazda "c" lamp, experiments were made with several types of bulbs and, finally, in the early part of 1915, the pear-shaped bulb was adopted. the long neck of the bulb, which acts as a cooling chamber for the heated gas is partially closed in the larger sizes by a mica disc to prevent the heated gas from coming into direct contact with the base. the development of new types of mazda "c" lamps continued, with an increase in the amount of light used for all kinds of work and has had a very marked effect on the design of street, industrial and commercial lighting systems of that time. before the advent of the mazda "c" lamp street lighting installations consisted largely of arc lamps of various types and some mazda"b" lamps. it soon became evident, however, that the mazda "c" lamp offered many advantages in the way of lower initial cost of units, greater flexibility, because of the wider range in sizes of lamps which are available for operation on the same system. in the industrial lighting field there was an increase in the use of artificial lighting, and mazda "c" lamps were being used in great numbers in this class of work. the larger sizes used in properly designed reflectors provided very satisfactory illumination for erecting sheds, foundries, railroad yards, etc., where the units had to be placed high above the work; while the smaller sizes were used in the general illumination of machine shops, textile mills, etc. it is, however, in the field of commercial lighting that the influence of the mazda "c" lamp was most apparent. the use of this type of lamp resulted not only in an increase in the intensity of illumination, but also in greater attention being devoted to the requirements of good lighting. a notable development in the lighting field involved the increased use of various media for modifying the color of the light in order to secure light of a particular spectral quality or to obtain certain desired effects in the lighting of interiors, etc., to which the mazda "c" lamp lent itself particularly well because of its high efficiency and the continuous character of its spectrum. artificial daylight units that employed mazda "c" lamps were being widely used where light of the same spectral quality as daylight is required, as in color matching, etc. formerly those engaged in such work were dependent on daylight, which was available only for a few hours in the day. now, however, work could be done anywhere and at any time by means of daylight units that employed the mazda "c" lamp, the operating cost of which was about the same as that of the carbon incandescent lamp