In order to carry out maintenance you need proper illumination. But what do we mean by proper illumination? We can distinguish between natural and artificial light. Both light sources have different light properties. This is clearly illustrated by our perception of color under different light sources. Natural light, for example, is best for recognising colors. If we look at colors in artificial light they can appear falsified. The greatest difference is reached with mercury vapour lamps. In this case, a red object appears as anything from orange to black. Better results are reached with candescent or fluorescent lightning. When the focus is not on color but on light efficiency, this fact changes and mercury vapour lamps do best here. So keep in mind: the proper light source depends on your working task.