Investigation of Calculation Method for Total Luminous Flux with Goniophotometry

As variation of light sources such as Solid State Lighting (SSL) increases, it is becoming more important to evaluate luminous intensity distribution and total luminous flux with goniophotometry. To reduce uncertainty and increase efficiency of total luminous flux evaluation with goniophotometry, we compare several existing calculation methods for total luminous flux evaluation. For the comparison, some incandescent lamps and LED lamps that differ with regard to luminous intensity distribution have been measured by a goniophotometer, and those total luminous flux values have been evaluated using the existing methods. The comparison results show that optimization for the angular measurement step taking into account not only beam spread angle but also details of luminous intensity distribution is required for reducing the measurement time and the measurement uncertainty simultaneously. To optimize the angular measurement step, modulation of the step in accordance with the 2nd derivative of the luminous intensity distribution is required.