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Technical Lighting – Sports Fields – Part 2 Lighting Requirements

On By luksmetrede Uncategorized

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.

Technical Lighting – Sports Fields – Part 1 Light

On By luksmetrede Uncategorized

Lighting is in every aspect of our lives now. With cheap LED’s, neons, discharge lamps, florescent lamps, cold cathodes giving us an endless choice to choose from. We use the best option for our requirement or as our lighting designer suggests or the architect approves.

However there are more technical uses of lighting such as tunnels, roads, sports fields, facades, etc. These kind of lighting require special attention and flawless lighting calculation and site supervision.

In this post I will try to explain general sports lighting and what the project managers should be aware of when selecting the best solution for their project. these will be just the basics and more details will be given in the future posts.

1) What is CRI? How does it help me?

CRI means “colour rendering index” and scales from 0 to 100. The colour change of 14 standard colours is calculated when an object is exposed to a specific light source and then this is compared to a reference illuminant of the same colour temperature (a black body* is used for colour temperatures up to 5000K and daylight above that). The CRI for a pair of light sources can only be compared if they have the same colour temperature.

In general terms, CRI is a measure of a light source’s ability to show object colors “realistically” or “naturally” compared to a familiar reference source, such as daylight. Sunlight has the perfect CRI which is 100. Higher the value better for your eyes therefore CRI>80 is usually chosen in sports fields to achieve good quality lighting however >90 is much better especially in sports fields with HD cameras. After all it helps us to see the “real” colours.

 

2) What is CCT?

Correlated color temperature (CCT) is a measure of light source color appearance defined by the proximity of the light source’s chromaticity coordinates to the blackbody locus, as a single number rather than the two required to specify a chromaticity.

The lighting industry to accept CCT as a shorthand means of reporting the color appearance of “white” light emitted from electric light sources. CCT values of most commercially available light sources usually range from 2700 K to 6500 K. CCT values are intended by the lighting industry to give specifiers a general indication of the apparent “warmth” or “coolness” of the light emitted by the source. According to lighting industry convention, lamps with low CCT values (2700 K to 3000 K) provide light that appears “warm,” while lamps having high CCT values (4000 K to 6500 K) provide light that appears “cool.” This convention may have been established because non-electric light sources with low CCTs, such as fire, connote warmth. However, this industry convention may be confusing to many people because the higher the CCT of the lamp, the “cooler” the light appears.

Current digital camera technology allows the video-produced media to be altered to ‘gain’ colour and contrast, as needed to produce the desired colour quality. Acceptable colour temperature for outdoor stadiums for all classes of competition is Tk ≥ 4,000. Selecting “cool” white colours is better.

3) What About Colour Consistency?

Color consistency refers to the average amount of variation in chromaticity among a batch of supposedly identical lamp sample.

The MacAdam ellipse is a system of colour measurement. It measures how much colour variation is possible around these axes, before the human eye detects a colour change. A series of ellipses can then be drawn around any target colour, and the closer any given lamp is to the target, the less colour deviation will be experienced when these lamps are placed side by side in an installation.

The distance from the target point in each ellipse is measured in SDCM. An SDCM of 1 step means that there is no colour difference between LED chips, 2-3 SDCM means that there is hardly any visible colour difference. Therefore smaller the number is better for our sports fields. MacAdam ellipse is much more popular in LED’s than any other type of light sources.