Mainconsiderations of Sports Lighting

Horizontal illuminance.

The illuminated playing field occupies a major part of the field of vision of anyone in the stadium, whether players, officials or spectators. Horizontal illuminance (Eh) represents the illuminance on the horizontal surface of the ground. It is mainly used to create a stable visual background in which the eye can distinguish between players and objects.

For non-TV lighting classes, average horizontal illuminance between 50-100 lux and 750 lux is required, depending on the motion and lighting classes discussed. For televised games, vertical illuminance is more important than horizontal illuminance; to ensure a balanced brightness of the TV picture, the ratio of average vertical to horizontal illuminance should match as much as possible, but should not exceed 0.5: 2. The horizontal illuminance should not be less than half or more than twice the vertical illuminance.

Vertical illuminance.
Players in any particular sporting event, and the balls they use, can be understood as vertical surfaces. This means that we need to first consider vertical illuminance lighting (Ev) when lighting them. In order to ensure the best field of vision and enable the human eye to identify the player from all directions, we should generally measure the Ev at a height of 1.5m, which roughly corresponds to the player’s face.
Experience shows that there is a close relationship between vertical and horizontal illuminance. For motion without a specific vertical illuminance standard, vertical illuminance is sufficient if the desired horizontal illuminance is achieved and the lighting design rules are followed.
Televised events involve exceptions to this rule of thumb; vertical illuminance has a significant impact on the quality of the final television or film picture. Television broadcasts typically require an average Ev of between 1000 lux and 2000 lux.

Uniformity.

Ensuring consistency is important to avoid adaptation problems for players and spectators. If the uniformity is not enough, it may be difficult to see certain objects or player details from certain positions.
Uniformity is expressed as：
The ratio of minimum illuminance to maximum illuminance (U1 = Emin/Emax).
Ratio of minimum illuminance to average illuminance (U2 = Emin/Eaverage).
In the case of non-television broadcasts, the uniformity of horizontal illuminance is usually specified to be 0.5 to 0.7 (Emin/Eaverage), depending on sports and lighting levels.
In TV scenes, high uniformity is essential for smooth and natural scenes, especially in this era of high-definition television; horizontal illuminance is generally 0.8, while vertical illuminance requires a uniformity value of 0.7 (Emin/Eaverage) in the direction of a fixed camera.
Even if the evenness ratio we define is acceptable, the change in illuminance can be disturbing if it changes too fast. This problem is most likely to occur when the TV camera is panning. Therefore, the illuminance uniformity of the TV / movie coverage of a grid point must be expressed as a percentage change relative to the average adjacent grid points. This is called a uniform gradient.
On a 4-meter computing grid, the common uniformity gradient of horizontal and vertical illuminance of the main camera is less than 20% to ensure smooth translation from one area to another.

Glare controlling.
Glare is a subjective factor. On the basis of extensive field research, CIE has developed a practical outdoor sports application evaluation system (CIE 112 Glare evaluation system for use in outdoor sports and area lighting).
CIE 112 defines a so-called glare rating factor (GR), which ranges from 10 to 90. The lower the glare value, the better the athletes’ glare perception in sports events.
Sports usually specify a maximum GR of 50.

Color properties.
The color properties of lamps and lanterns have two important aspects:
The color appearance of the light. This is the color impression of the overall environment created by the light source.
The color rendering property of the light source used, or the CIE color rendering index (CRI). This describes how the light source faithfully reproduces a series of colors.
The indication of the color appearance of the lamp can be obtained from the relevant color temperature measured in Kelvin (K) degrees, which mainly varies between 2000 and 6500K. The lower the color temperature, the warmer the color impression of light; the higher the color temperature, the colder or bluer the impression of light.
Sports lighting generally requires a color temperature between 4000 and 6500K.

The color rendering of a light source can be expressed by its color rendering index, which is expressed by a numerical value between 0 and 100. A light source with a CRI of 100 will faithfully present the scene color, using daylight as the comparison standard. Color perception is highly relevant to most motion applications.

Although some of the color distortion caused by artificial lighting is acceptable for non-television activities, television broadcasting requires highly accurate color reproduction.

The shift from traditional lighting to LED lighting has triggered a discussion about whether CRI is still the correct color fidelity indicator for television broadcasting. It is developed based on the human eye response curve and a set of soft colors, and is not necessarily suitable for sports broadcast cameras that transmit colorful images.

The European Broadcasting Union (EBU) has developed a television lighting consistency index (TLCI) based on camera response. As a color indicator designed to meet its needs, TLCI is becoming more and more popular among broadcasters. Discussions on this topic are ongoing, but there is a general consideration that it should be easy to get the correct color when TLCI > 80.

Flicker.

Because of the phase of light, a special problem with ultra-slow-motion cameras is the flicker of 50Hz.
Due to the uneven ratio between the scanning frequency of the camera and the alternating amplitude of artificial light powered by the power frequency, the camera will perceive a change in the level of light. .
This effect is visible only during slow motion playback and is called the flicker effect.

Sports federations have begun to incorporate so-called flicker factors into their lighting recommendations. To avoid flickering of any visible slow-motion images, it is recommended that the flicker coefficient be less than 3%.

Spill light controlling.
Stray light from outdoor lighting can disturb people nearby: for example, drivers on adjacent roads and residents of nearby houses. Local or municipal authorities sometimes develop their own guidelines on such issues.

In the absence of guidelines, the European standard EN 12193 has defined interference light limits in accordance with CIE recommendations. The key criteria here are the vertical illuminance of the attribute, the luminaire intensity of each light source in the direction of potential interference, the amount of light emitted above the horizontal plane passing through the center of the luminaire, and the glare level experienced by the driver in the area.