Instrument consists of three main parts: the illuminometer proper, a controller, and a reference standard. All are stored in a black case, dimensions of which are 42x25x18 cm. Also included in the case are various accessories, including three electrical cords. This device was used as a portable illuminometer. The illuminometer proper is a black tube, 23 cm long and 4.5 cm in diameter. It operates by comparing the brightness of a surface with a translucent lamp of known intensity at a variable distance within the illuminometer. One of the accessories within the case is a white test plate, with essentially constant brightness from all angles of observation. The scale of the instrument, at one end of the illuminometer proper, is calibrated in foot-candles, and the user standardizes it themselves to allow for the absorption of the surface. The controller consists of a battery for operating the lamps, a milliammeter for use with the standard lamps, two close-regulating rheostats, and a double-throw switch. The reference standard consists of a metal housing in which is mounted a standardized lamp. It is used, along with the test plate, to calibrate the illuminometer.
CRM
