The black curve shows the spectral distribution of the Sun above the Earths atmosphere (called Air Mass Zero).

The coloured curves (red, green, blue) show the external quantum efficiencies of a standard triple-junction solar cell of Azur Space GmbH, Heilbronn, Germany.

The external quantum efficiency (simplified) is a physical measure to express which percentage of the incoming light on to a specific solar cell can be translated into electrical power i.e. Numbers of electrons out per photon in.

The bright light blue curve represents the simulated Sun spectral distribution achieved with the sun simulator equipment.