The unit is encased in a special aluminium case with standard stem of 9mm dia. It is fitted with high class optics. Light from two different sources falls on either side of a uniform opaque white screen. This light is reflected by side reflectors (Special prisms) and passes through the Lummer Brodhum cube.The field of view can be seen through a telescope and the light intensities are compared directly. The photometer is mounted in a swivel bracket for proper adjustment with two-nose lamp house & electric bulb is in a metal cased with cord & pin finished optical block.