Floodlighting dazzles neighbours: what applies and what helps

Light counts as an emission under the Bundes-Immissionsschutzgesetz (BImSchG, Federal Pollution Control Act). The legislator has not set limit values of its own for light. The LAI guidance therefore gives the authorities benchmarks: if the guideline values are exceeded, there is as a rule a significant nuisance. The guidance expressly mentions floodlights at sports facilities.

Assessment is based on the perception of an average sensitive person. Which values apply follows from the development plan, otherwise from the actual use. Individual states have implemented the guidance in their own regulations, so ask your pollution control authority.

Brightening is measured as the average illuminance in the plane of the window, and for balconies and terraces at their boundary. Guideline values between 6 am and 10 pm and between 10 pm and 6 am:

• Spa areas, hospitals, care homes: 1 lx and 1 lx
• Residential areas, small settlement and recreation areas: 3 lx and 1 lx
• Village and mixed areas: 5 lx and 1 lx
• Core, commercial and industrial areas: 15 lx and 5 lx

The values refer to light that burns several times a week for more than an hour each time. For less frequent or shorter operation, the guidance provides for an assessment of the individual case.

Glare can also be disturbing from a greater distance, even when there is hardly any extra brightness at the window. The eye is drawn again and again to the bright light source. The guidance assesses this with a glare measure based on the luminance of the light source, the ambient luminance and the solid angle.

The guideline value k is graded by time. In a residential area it is 96 from 6 am to 8 pm, 64 from 8 pm to 10 pm and 32 from 10 pm. In village and mixed areas it is 160 until 10 pm and 32 after that as well.

It is best to take the neighbourhood into account in the lighting design from the start. The LAI guidance names these proven measures, among others:

• Direct light only where it is needed, avoid stray light
• Aim lighting from top to bottom; the light source should if possible not be visible from the homes
• Use additional shields and luminaires with a limited beam angle
• On sports grounds, use floodlights with asymmetric light distribution and no light above 80°
• Use higher masts in combination with asymmetric flat-glass floodlights
• Limit operating time, switch off or dim at night
• Retrofit old systems

For an existing system, the authority decides in the individual case. According to the LAI guidance, for sports facilities it takes into account the lighting requirements of the sport, such as regular lighting. If a residential area and a sports ground have long been close together, there may be a duty of mutual consideration.

Sensible first steps are a survey of alignment, mast height and operating times, and a conversation with neighbours and the authority. For a legal assessment of the individual case, consult a specialist.