The National Census of Sports Facilities in Italy carried out by CONI in collaboration with the National Institute of Statistics and the Credito Sportivo shows that in Italy there are around 119,000 sports facilities of various kinds, 61% located in the north. More than half are artificially lit but only 28% are indoors (Antonelli 1986). The lighting of these facilities has an important social purpose as it allows for a longer period of use and no one can reasonably cast doubts on the importance that sports education has in the development of an individual’s personality. It is estimated that a plant located in Milan has a 40% higher utilization rate if lit.
The lighting of sports facilities is bound by specific needs which cannot be ignored. Unfortunately, these leave little room for modifications in the projects that could lead to a lower level of light pollution, unlike what happens for other external lighting systems such as street lighting which can be easily improved from this point of view. Therefore, if not suitably and carefully designed, the lighting of sports facilities can constitute a significant source of light and optical pollution.
Let’s see how the main needs are reflected in light pollution bearing in mind that each sport should be examined individually.
We can assume that athletes and players primarily want to win the game and put on a show. To achieve this, they require an excellent visual performance from the lighting system, i.e. that it allows them to see well and have perceptions in a short time. They also need the best possible visual comfort. This means that a rather high level of illuminance is required and consequently the amount of light scattered into the sky by the ground is high. The speed of perception increases proportionally to the illuminance and reaches the maximum regime with a few hundred lux. The level of illumination required therefore depends on the type of sport. In fact, to see fast moving or small objects well, greater than for larger or slower moving objects. Stadiums with large numbers of spectators where the outermost stands have a considerable distance from the field require a greater quantity of light because as the distances increase, the objects observed decrease in size and therefore it becomes more difficult for the judges to identify them by contrast with respect to the background, referees and spectators. Sponsors also want advertising messages on the sides of the field well lit and public safety authorities also want public areas well lit. In large stadiums, the level must allow for the use of surveillance cameras.
Performance and visual comfort also require that the lamps have good color rendering so as to allow good color reproduction (for example, players must be able to easily distinguish the opponents’ shirts). Therefore monochromatic lamps such as low pressure sodium lamps cannot be used but metal halide type lamps are usually used instead which allow to obtain a more homogeneous distribution of the light emitted at the various wavelengths even if at the expense of a lower efficiency and of a shorter duration. High pressure sodium lamps sometimes accompany the previous ones but only in order to produce a warmer overall light. As we shall see, the spectrum of a metal halide lamp extends almost continuously from red to blue. Therefore, lighting with lamps of this type is excellent from a sporting point of view but must have the minimum dispersion possible, under penalty of heavy disturbance in the observation of the sky which cannot be eliminated with any filter.
The type of sport also imposes heavy conditions on the arrangement of lighting fixtures (projectors and lamps). For example, soccer players need lateral lighting (called vertical) to see the ball from the sides and from below: lighting from above (called horizontal) would not allow them to see the ball except on the ground. Furthermore, it is necessary to guarantee safety in use, which places further constraints on the arrangement of the lighting fixtures which must be located outside the playing area to avoid collisions and breakages. Therefore, in stadiums, lighting generally comes from not too high light towers located on the sides of the field where, in general, from 6 to 24 floodlights are installed which, in order to illuminate the field, must have inclinations with respect to the vertical from 50degree to 68degree(maximum value prescribed to avoid dazzling the players). If the projectors, despite being of the narrow beam type, radiate a far from small amount of light even beyond the 30-40 degree from their axis, as often happens, it is clear that the light towers end up illuminating directly above the horizon disturbing motorists and polluting the sky.
Television shooting requires a quality visual performance. This means particularly high levels of illumination especially in the case of high definition TV shooting which also require 2500 lx of illuminance on the ground, compared to the 100 lx which are generally considered sufficient for training and the 12 lx which the Commission Internationale de l’EclairageCIE ) is recommended on roads with medium traffic intensity. It turns out that the Italian stadiums built for the 1990 World Cup, where high-definition filming was planned, they were the most illuminated on our planet with powers used ranging from 920 kW (kilowatt) (Meazza-Milan) to 1270 kW (Florence) for ground illuminances from 1500 lx to 2800 lx against the 25-300 kW of the usual football fields which are illuminated with 100-1000 lx. Luckily some of them such as the Meazza in Milan have been designed in a modern way by inserting the lighting in the side cover of the stadium, which should limit the dispersion of light.
In this complex and heavily conditioned framework there are some spaces to achieve a decrease in light pollution. First of all, it should be remembered that the sports clubs are interested in a low cost of the system and management and therefore have common interests in energy saving and in the elimination of light dispersion. Furthermore, the architects seek the best possible visual impact and advanced technology. Therefore, if on the one hand the search for the effect can be a source of light pollution, on the other hand the interest in the search for new, less polluting solutions can be a source of interest and satisfaction for them.
The technical possibilities for limiting the dispersion of light are based on the fact that what is achieved today with watts should be achieved with technology. In particular, projectors capable of avoiding glare and upward light radiation, such as asymmetrical ones or those with an internal screen, should be used. A useful design expedient consists in offering the possibility of scaling the level of illumination in cases of high competition, ordinary competition and training. For example, at the Olympic Coliseum in Calgary there are 12 different combinations ranging from 160 lux for training to 1400 lux for TV shooting.
Installers are often interested in ease of installation and compliance with current legislation which should therefore also take this problem into account. In Italy the task of elaborating and publishing standards in this field is entrusted to the CNR (Commission for lighting) which avails itself by delegation of the Italian National Unification Body UNI (Commission for sports and recreational facilities and equipment) which collaborates in the preparation of the rules with CONI through a UNI/CONI Sport Commission. The main standard in this sector is UNI 9316 (Sports facilities – Lighting for color shooting – Requirements) in which it is expressly prescribed that “The light pollution produced by the lighting system outside the sports facility.