Abstract : Type Ia supernovae used as cosmic distance indicators are one of the pillars of the current cosmological concordance model. The instrumenting work in the first part of this thesis was done in the framework of a project using these objects, the SNAP satellite, for which it is necessary to build a space-worthy large focal plane including CCD detectors for the visible range and APS for the infra-red. To test the readout of these detectors at very low noise levels, we have built two cryogenic test benches and studied an analogic ASIC. The second part shows the analysis of existing data within the framework of our "calorimeter" model to improve the use of SN Ia as standard candles. GRATIS is a programm designed to calculate the decay energy deposition within the supernova. Comparison with the measured luminosities is satisfactory. Other possible improvements come from the evolution of spectra at late times and from the color jump we call "green ray".