With the passing of time, luminaires and room surfaces get dirty. In addition the light output from lamps decreases as they age. The illuminance from a lighting installation therefore decreases. Lack of maintenance means that a lighting installation is not performing at its best and energy and money are being wasted. Many installations are poorly maintained and simple cleaning of lamps and luminaires can often substantially improve the lighting of the space so that the benefits of consuming energy to produce light are fully realised.

Maintenance requirements should be considered when installations are designed. Luminaires which are easily accessible are more likely to be cleaned regularly and have their lamps replaced. Some luminaires are designed specifically to reduce the need for maintenance, e.g. self-ventilated luminaire resist the accumulation of dirt on optical surfaces.

Proper cleaning materials and techniques should be used to minimize losses caused by chimical action or scratching of optics and electrostatic dust accumulation.

Plastic diffusers or prismatic controllers discolour with age and reduce the light output from a luminaire. Replacement of these in old installations can produce a significant improvement. Plastics which are UV stabilised should be used, as they also generally have the longest useful life.

Light output of fluorescent lamps decreases over time, so that a lamp may still consume the same power as when new but give perhaps only half as much light or less before actually failing. The bulk replacement of lamps on a planned basis at the end of their useful life, before light output depreciation goes beyond acceptable limits, should be considered, with the spot replacement of any earlier failures. A planned cleaning and relamping, coinciding perhaps with a holiday period to reduce disruption to staff, can ensure that light losses are minimised and the lighting installation is always working efficiently.

The decrease in light output through the life of a lighting installation is usually allowed for in the initial design, so that when new the illuminance can be somewhat above that required unless dimming or constant lux controls are used in the design or fitted. Designing with controls would prolong lamp life and overcome any problem of over-design.

Cleaning luminaires may be dealt with as a separate issue as the degradation of the luminaire will be dependent on the conditions in which they are fitted. For example, retail premises with open-door trading policies operating in a busy traffic way will require higher cleaning ratios that an office with no opening windows which is air-conditioned.