Page 35 - Energize December 2022

TECHNICAL

Uniformity An indication of a lamp’s colour is its correlated colour
Ensuring uniformity is important in avoiding adaptation problems temperature as measured in degrees Kelvin (K), which varies
for both players and spectators. If uniformity is inadequate, between 2000°K and 6500°K. Sports lighting generally requires
certain objects or player details might be difficult to see from a colour temperature of between 4000°K and 6500°K. The
certain positions. colour rendering properties of a light source can be indicated
by its Colour Rendering Index (CRI), expressed as a numerical
Uniformity is expressed as: value between zero and 100. A light source with a CRI of 100
U 1 - The ratio of the lowest to the highest illuminance will represent scene colours faithfully, with daylight as the
(U 1 = E min/E max) standard of comparison. The transition from conventional
U 2 - The ratio of the lowest to the average illuminance lighting to LED lighting poses the question of whether CRI
(U 2 = E min/E ave) remains the correct colour metric for television broadcasting.
It was developed based on the human eye response curve and
In non-televised situations, the uniformity of the horizontal for a set of pastel colours and isn’t necessarily appropriate for
illuminance is generally specified as between 0,5 and 0,7 sports broadcast cameras that transmit images rich in saturated
(E min/E ave), depending on sport and lighting class. In televised colours.
situations, high uniformity is necessary for smooth and natural-
looking scenes, especially in this era of HDTV; horizontal Lighting the spectator areas
illuminance is generally 0,8, whereas vertical illuminance in the Adequate horizontal illuminance is key to ensuring spectators’
direction of fixed cameras requires a uniformity value of 0,7. safety of movement as they enter or leave the stands and
Even when the uniformity ratios are acceptable, changes in other premises. A TV broadcaster may specify a spectator-area
illuminance can be disturbing if they happen too quickly. This lighting level as a ratio of the field-of-play lighting level to suit
problem is most likely to arise when a television camera pans. its production style. If dedicated luminaires are being used
The illuminance uniformity for TV coverage at a certain grid to illuminate areas for spectators, they should have a colour
point thus has to be expressed as a percentage change from temperature that matches as closely as possible the colour
the average adjacent grid points. This is called the uniformity temperature of the field-of-play’s lighting. The flicker factor
gradient. A common uniformity gradient value for both should also be similar to that of the field-of-play’s lighting.
horizontal and vertical illuminance, in the direction of main
cameras of ≤20% on a 4 m calculation grid, might ensure smooth Spill light
panning between one area and another. Stray light from outdoor lighting installations can disturb drivers
on adjacent roads and inhabitants of nearby houses. Local
Colour properties authorities sometimes maintain their own guidelines on such
The colour properties of luminaires have two important aspects: matters. Where no guidelines exist, European norm EN 12193
• The colour appearance of the light. This is the colour has defined obtrusive light limits based on CIE recommendations.
impression of the total environment that the light source The key criteria here are vertical illuminance on properties, the
creates. luminaire intensity in a potentially obtrusive direction of each
• The colour rendering properties of the light source used, or light source, the quantity of light emitted above the horizontal
the Colour Rendering Index CRI). This describes how faithfully plane that passes through the centre of the luminaire, and the
a light source can reproduce a range of colours. level of glare that drivers might experience.

Sport Illuminance (Lux) Uniformity Glare CRI
Rugby/soccer
I 500 0,7 55 70
II 200 0,6 55 60
III 75 0,5 55 60
Outdoor tennis
I 500 0,7 50 70
II 200 0,7 50 60
III 200 0,6 50 50
Cricket (class I)
Pitch 750 to 1500 0,7
Outfield 500 to 750 0,7
FIFA world cup 2000 (average) >0,7 <50 >80
Table 1: Stadium lighting requirements

energize | December 2022 | 35