When designing a sports field there are certain international and national lighting requirements. Some are what many people already know or heard before however creating the best design is hidden in details. Here we will see take a general look at all of them.
1) Lighting Levels
Light Level or illuminance is the total luminous flux incident on a surface per unit area. In sports fields this area is the playing area and what the lighting designers usually calculate is the horizontal value of the lighting level. But we need to deeper to fully understand sports lighting.
a) Horizontal illuminance(Eh); is the amount of light falling on a horizontal activity plane, this is usually the height of the playing surface (1 meter above pitch for football, 0,75 meter for table tennis).
b) Vertical illuminance(Ev); refers to illuminance towards a fixed or field camera position. however vertical illuminance can also refer to a spectator location. Vertical illuminance directly effects the quality of the camera recording and the spectators eye comfort.
c) Semi-cylindrical illuminance(Esc); is the appropriate descriptive parameter, as shown by experiments carried out under real outdoor conditions. Briefly, Esc is defined as the averaged illuminance on the curved surface Asc of an upright half cylinder. Currently in most sports fields there is no required level for Esc but a lighting designer has to calculate and achieve good uniformity for the best lighting possible. Below image shows Esc and helps better understand it.
In sports area lighting, depending on the class of the field, different classes are set by each federation. These classes have varying lighting levels set for horizontal and vertical illuminance. Televised events, national and international matches and audience number increases these levels. Since all sports fields have different requirements more details will be given in the upcoming posts.
2) Lighting Uniformity & Uniformity gradient
Lighting uniformity has two main components;
U1: Uniformity of illuminance; calculated as E min/E max
U2: Overall uniformity of illuminance; calculated as E min/E ave
*Eave Average illuminance on a grid; Emin Minimum illuminance on a grid; Emax Maximum illuminance on a grid.
These components give us an idea of our lighting designs’ quality however uniformity gradient (Eg) is much more important in my opinion and usually missed in lighting requirements. Ug is the the percentage difference of illuminance between adjacent grid points so even when we have the optimal lighting uniformities we might have low Ug resulting in zebra effect. To avoid this lighting designers should have the lowest Ug values as possible.
3) Shadow Control
Hard line shadowing is one of the biggest problems in any sports field. Also its one of the hardest to avoid too. To minimize the shadows lighting designer needs to multi-zone aim the luminaires while still considering the glare and uniformity effects. Shadow control is a very specific issue itself and will be further explained in the upcoming posts.
4) Glare
Glare is a visual sensation caused by excessive and uncontrolled brightness. It can be disabling or simply uncomfortable. It is subjective, and sensitivity to glare can vary widely. However glare can be calculated and it has a value between 0-100, where 100 is unbearable glare and 0 is unnoticeable. For sports fields we usually need glare below 50 for the players viewing angles.
To avoid glare we need to use special reflectors, baffles and asymmetrical luminaires.
5) Reflection
Reflection is a highly ignored disturbance especially in indoor sports field lighting. Reflected light from the ground or walls can be very disruptive to both spectators and cameras. Since reflection can not be avoided by changing the colour of the playing fields’ ground a lighting designer has to be extra careful and not aim the luminaires towards the camera viewing angles. Luminance values should be checked for each of the camera position.
6) Flicker
Light flicker refers to quick, repeated changes in light intensity – light that appears to flutter and be unsteady. It is caused when the voltage supplied to a light source changes or when the power line voltage itself fluctuates. Flicker is considered a challenge with HD camera broadcasting and slow motion recording. There are several ways to avoid flicker, special flicker free ballasts, 150Hz or higher output ripple drivers, etc. I will explain flicker with more details on specific sports fields in the upcoming posts.