Errors In Luminous Intensity Measurements And Photometric Performance Of Linear Sources Due To The Length Of The Measuring Distance.

The previous published work in the area of this investigation was completed in 1963 by W Riggs and A Lampert. At that time the main consider was the effect of short distance photometry on efficiency and utilization factors. Since that time other considerations have been introduced into lighting design and the optical control in luminaires has altered significantly. This report considers the requirements for the accurate photometry of linear luminaires equipped with low pressure mercury vapor fluorescent lamps, the design requirements of an intensity distribution photometer, and the effects of errors in the mechanical and optical systems of the photometer. A unique design of variable Light path intensity distribution photometer: vertical angle indicating system have been developed, constructed, and commissioned, and the photometer has been used to measure the intensity distribution of eight types of twins {500mm tubular fluorescent lamp luminaires and the measurements have been performed at both 2.9m and 7.9m. The output of the detector of a photometer is proportional to the flux falling on the cell. The cell output must be converted, using an appropriate calibration factor, to an intensity value. Two methods of calibration have been examined and the photometric data produced using both methods have been compared. A number of computer programmes have been developed to enable the intensity distributions at the above distances to be compared and the complete photometric data for the luminaires to be calculated and the effect of using a short photometric distance evaluated. The effects of the application of the photometric data, which has been derived from both the long and short distance photometry, to the design of lighting installation have been compared for room size from 4m x 4m to lighting installations have been compared for room. 2Um x 20m. The effects of the use of the short distance intensity measurements on the by 5 parallel and perpendicular plane aspect factors and direct illuminance calculations have also been considered. From the measurements and subsequent comparisons of the calculated s installation design data the general conclusion is that the photometry at a 4 photometric distance: luminaire length ratio of 2:1 will produce reliable and acceptable lighting design data and that lighting designs produced sing this data will be virtually identical to those designed using data produced at a 5:1 ratio.