Floodlighting too dark or uneven: causes and remedies

The floodlighting guide from the football associations of Saxony, Saxony-Anhalt and Thuringia describes typical defects in existing systems. Together with licht.wissen 08, this gives the following list:

• Lamps: luminous flux decreases with operating time, individual lamps fail or are unsuitable
• Dirt: dirt and ageing of the luminaire reduce the light that reaches the pitch
• Alignment: if possible, every position on the pitch should receive light from at least two luminaires, otherwise hard shadows are likely
• Masts: according to the association guide, in existing systems they are often only 8 to 12 m high, which favours glare, poor lighting and large shadow areas
• Layout: often only one half of the pitch is lit, and many masts alone do not yet mean good lighting quality
• Trees: tree crowns that have grown too close to the pitch disturb the light distribution
• New need: if running tracks surround the pitch or the team plays at a higher level, the old design may no longer be sufficient

The standard values for average illuminance are maintained values. They must never be undercut, and once they are reached, maintenance is required. So that this does not happen shortly after commissioning, the planning sets the new-installation value higher by a maintenance factor.

The factor takes into account luminous flux depreciation, lamp failures, and dirt and ageing of the luminaire. If it cannot be determined, licht.wissen 08 gives the reference value 0.7 for outdoor facilities. With a maintained value of 75 lx, this would give a calculated new-installation value of about 107 lx.

For your system this means: ask which factor and which maintenance method were agreed in the planning. If there are no documents on this, only a measurement shows how much light still arrives today.

According to the association guide, the area is divided into a uniform grid in accordance with DIN EN 12193. In each grid cell the illuminance is measured with the floodlights switched on, horizontally at ground level. The result should be documented in writing. The measuring points give:

• Average illuminance Em: is the system bright enough overall?
• Lowest value Emin: where is the darkest spot?
• Uniformity Emin / Em: is the light evenly distributed?

For football, the reference values are Class III with 75 lx and 0.5, Class II with 200 lx and 0.6, and Class I with 500 lx and 0.7. A good average with poor uniformity points more to alignment, masts or obstacles than to a system that has aged overall.

The association guide names a drop below 80% of the nominal illuminance as the limit from which repair or maintenance is needed. After that it requires a new measurement report and, before recommissioning, an inspection by a qualified electrician in accordance with DGUV Regulations 3 and 4.

First the measurement, then the intervention. After that, the obvious points can be worked through:

• Replace defective lamps and ballasts as long as they are still available
• Clean the floodlights
• Check alignment against the lighting calculation, if still available
• Deal with tree crowns in the light path

Work on masts and electrics belongs in the hands of specialist companies. The association guide names defects such as unacceptable cables and insulation faults, which are frequently found in existing systems.

There is no fixed limit, but some signs point to switching:

• Spare parts are hardly available any more: the city of Landsberg am Lech found this with its system from 1976 and retrofitted
• The system is due anyway: according to a 2017 reply, the city of Mainz automatically converts to LED when a system has to be replaced because of age or defect
• The measured values stay below the class value even after maintenance
• The class rises, for example from training to competition
• Electricity and maintenance costs are to fall

At the Sportplatz am Nocken, the city of Wuppertal went from six masts with metal halide lamps and 120 lx to four masts with LED and around 200 lx. There, however, the pitch was also rebuilt. Whether this is possible at your facility is only shown by the lighting calculation with the existing mast positions.

Before you retrofit, clarify the structural engineering and funding. According to the association guide, LED floodlights can be heavier than the old luminaires. A pure lamp replacement is not funded under the Kommunalrichtlinie, and no order may be placed before the funding decision.