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.