The effects of solar simulator xenon flash lamp ageing and spectral output measurement uncertainty on the spectral mismatch are investigated. Initial measurements demonstrated that the spectrum of an older lamp set has a relatively lower blue and larger red content compared to a new set of bulbs. Measurements over the life-time of several sets of bulbs however, showed large unexpected variations due to measurement uncertainty in the spectral measurements themselves. The main influencing factors are investigated and a faulty temperature control is found to be the main source of uncertainty. It is shown that this alone can affect the mismatch calculation to a larger degree than the MMF would correct in itself
