Goniophotometer graph,candelas

Cardiff E.T.T. Goniophotometer seen here ready for testing prior to shipping to Hong Kong Polytechnic University for installation. Similar to Photometer 1, this is an Angular Photometer, providing directional light emission data. During use, the light fitting (luminaire) is mounted on the top circular plate, and revolves slowly while the optical measurements are made. The photometer system with this configuration is a calibrated silicon cell and amplifier mounted ten meters away. All apparatus is in a darkened, black-painted room in the final installation, to keep out stray light. The movement and the measurement device are under computer control, with microcontrollers performing the local instructions for all the hardware. The microcontroller systems are custom built by Cardiff ETT.

An output graph is shown here, representing the angular and intensity data for a standard domestic lamp in terms of altitude, azimuth and the luminous intensity in units of candelas. The software can be customised for the user.

The goniophotometer complies with CIE standards (Commission Internationale de l'Eclairage) and British Standards. In this context it is known as a 'C-Gamma goniophotometer', which refers to the orientation of the readings taken. The data are used in the characterisation of lighting assemblies.

(Facilities acknowledgement: BM Cross. )