A telescope calibration method for type Ia supernovae photometry is proposed. It is based on the direct illumination of a telescope with a calibrated multi-LED light source. Its description includes traceability of the calibration process and check standard to maintain 0.2% accuracy over years period. Although opto-electronics read-out and control could be built from commercial off-the-shelf components, we report on developments relevant for large systems. Their requirements are tailored on a proposal for the SNLS experiment performed on the Megaprime instrument installed in CFHT for which our R&D is performed. Similar LED systems of larger size are working in high-energy physics optical calorimeters
