In simple terms, Electroluminescence (or EL as its often known) involves the injection of a reverse current into a module or string. This is usually between 3-5 amps depending on the modules. This reverse current flowing through the cells of the module causes a luminescent effect that can be seen at night (or low light levels).
Instead of absorbing light through the cells for power output, the input power shines out through the cells showing itself in a very narrow band of light in the Electroluminescence range. This light is invisible to the human eye, but can be detected by specialist EL cameras (modified DSLR’s).
Images of the luminescing modules are captured by the camera, and this method enables you to clearly see areas of power producing cells (bright white/grey areas) and non-producing parts of the cells (dark grey / black areas, cracks, defects). These dark areas show electrical isolation (grid finger separation) and will negatively effect the power output of the module. Evidence can also be captured of a range of deterioration phenomena and manufacturing quality issues (like PID or flux corrosion for example).
Any questions on this cool technology, please let us know ;o)