What’s the right choice of colour temperature for airport apron lighting?

Good lighting isn’t all about visibility and uniformity, and that’s particularly true in commercial environments such as airports. One of the questions that we’re often asked in relation to aviation lighting—specifically lighting around the apron—is which choice of colour temperature is best. 

In this post, we’re going to take an in-depth look at the principles of colour temperature as it relates to light-emitting diodes (LEDs). We’ll discuss what colour temperature is, why it matters, and how aviation professionals can ensure that they make the correct choice for their own apron lighting needs.

What is correlated colour temperature?

Correlated colour temperature (CCT) is the term we use to describe the hue of a light source. CCT is measured in Kelvins (K), and the higher the number of Kelvins, the “colder” a light appears.

For instance:

• At 3000K, a light source will produce warm white light, similar to an incandescent bulb
• At 4000K, the warmer and cooler tones are balanced, creating a neutral white light.
• And at 5000K, you get a cool white that resembles natural daylight.

As a term, CCT originates from the fields of physics and colour science. CCT describes the colour of light from a specific source (like a luminaire) as it compares to that produced by a theoretical reference body. In this case, that theoretical reference is what’s known as a “blackbody radiator”. 

A blackbody radiator is an idealised physical body that absorbs all incident electromagnetic radiation and re-emits it as a spectrum of light. As the blackbody is heated, it emits light that changes colour depending on its temperature.

For example:

• At lower temperatures, the light emitted is red or orange (resembling the colour of a candle flame).
• As the temperature increases, the light shifts to white and then to bluish tones (like daylight).

The concept of CCT is rooted in Planck's law of blackbody radiation, and its practical application in lighting design comes from the need to describe the appearance of light in a simple, standardised way.

Different CCTs are typically used in different environments, and you can see this in action in a typical home. In a lounge or bedroom, for instance, lights tend to sit around the 2700-3000K mark. In a kitchen or bathroom, they’re more likely to be closer to 4000K. So, why is that the case?

Why are different CCTs used in different environments?

To understand why different CCTs may be selected for different environments, it’s first important to understand that different colour temperatures have a significant impact on our bodies. The greatest impact is felt in our eyes (specifically our retinas) and our brains. 

• The retina
  Our retinas contain photoreceptors—cells that transform light into electrical signals that can be processed by the brain. The three main photoreceptor cells are rods, cones, and what’s known as “Intrinsically Photosensitive Retinal Ganglion Cells”, or ipRGCs.
  
  
  •  Rods are sensitive to low light levels, but aren’t capable of perceiving colour.
  • Cones are responsible for colour vision and function best under bright light.
  • ipRGCs help to control “non-visual” responses to light, like circadian rhythms.

• The brain
  Exposure to different CCTs can impact the secretion of brain hormones. Blue light suppresses the production of melatonin, for instance, which can lead to increased alertness. It can also help to enhance serotonin production, which can improve our moods and focus. And the production of cortisol—sometimes known as the “stress hormone”—is also triggered by blue light.
  
  

Because different CCTs impact the production of hormones in this way, it tends to make warm, neutral, and cool white more appropriate for specific airport environments. In this second table, you can see where lights at different colour temperatures are best applied.

For apron lighting, then, cool light is the clear and correct choice. Cool light can help to keep pilots and ground staff alert, productive, and motivated, while simultaneously fending off the need to sleep. This isn’t the only reason that cool light is the most appropriate choice, however.

Where else can CCT have an impact at an airport?

The use of cool light on an apron can also have a major impact on safety and security. This is because cooler CCTs enable security cameras to perform better, and make it easier to recognise human faces.

•  Camera performance
  White light improves image quality by providing better illumination, colour fidelity, sharpness, and contrast. This can be particularly important for cameras used for facial recognition purposes, as the richer image enhances the algorithm's ability to detect and analyse faces correctly.
  
  
• Face recognition
  The same principles apply to human face recognition, too. White light enhances the visibility of facial details, making it easier for people to identify key features. That means it not only improves security as a whole, but the feeling of safety, too.

How do lighting manufacturers create different CCTs?

We now know which CCTs are best for aviation environments. But how exactly do LED Chip OEM Manufactures create specific colour temperatures?

The answer lies primarily in the makeup of the LED chips that sit within a luminaire, and the way in which those chips interact with different coatings. 

• LED chip materials
  An LED chip is the part of a luminaire that converts electrical energy into light. Different materials can be used in the creation of an LED chip, and these materials emit different wavelengths of light. Most “white” LEDs are actually blue, for instance, using a phosphor coating to convert parts of the blue light into other colours. 
  
  
• Phosphor coatings
  A phosphor coating is a layer of luminescent material that emits light when exposed to radiation or other kinds of energy. To create white light, a phosphor coating can be applied over a blue or ultraviolet LED chip. That coating absorbs some of the blue light, and re-emits it as yellow or red light. This combination then creates white light. 
  
  Different types and thickness of coating can influence the CCT. A thicker or more red-emitting phosphor produces warmer white light, while a thinner or more yellow-emitting phosphor produces cooler white light. By controlling the blue light in this way, manufacturers can essentially “finetune” the CCT.
  
  
• Multiple phosphors
  In some cases, multiple types of phosphor coating can be used to adjust both the light spectrum and the CCT. The right balance between red, green, and blue components in the emitted light determines the overall warmth or coolness.
  
  By employing these techniques, manufacturers can produce LEDs with CCTs that vary from warm to cool. This is important—not just because cooler CCTs are better suited for the needs of airports, but because luminaires in that temperature range also tend to be more efficient to run.

Why are luminaires with cooler temperatures more efficient?

A luminaire running at 5000K is more efficient than one running at 3000K, and there are four main reasons for this:

1. The human eye tends to be more sensitive to cooler lights
   Our eyes are more sensitive to certain parts of the visible spectrum. The blue light emitted by higher CCT LEDs tends to have more in energy in the part of the spectrum where our eyes are most sensitive, meaning that we tend to perceive it as being brighter.
   
   
2.  Converting cool light to warm uses up energy
   As noted above, to convert cool light (blue) into warm (red or yellow) light, you need to filter it through a phosphor coating. This conversion process isn’t perfect, and some of the energy produced is then lost as heat. The blue light emitted by an LED chip in a higher CCT LED requires less conversion, so less energy is then lost as a result.
   
   
3. It takes less energy to create cool light
   Different coloured light has different wavelengths. Blue light, for instance, has a shorter wavelength. Red light has a longer one. Why does this matter? Because shorter wavelengths are also associated with higher energy photons, and longer wavelengths with lower energy photons. That means that it takes fewer photons (i.e. less energy) to create the same level of perceived brightness with blue light than it does with red.
   
   
4. Creating cool light generates less heat
   Higher CCT LEDs often generate less heat during the conversion process compared to lower CCT LEDs. The more heat an LED generates, the less efficient it becomes—with  a portion of the electrical energy wasted as heat rather than being converted into visible light.
   
   

And why does efficiency matter when it comes to airport lighting?

Efficient lighting delivers three key benefits for airports—it reduces the amount of energy they use, can lower their carbon footprint, and minimise the number of luminaires that are required.

• Energy savings
  Greater efficiency means that LEDs produce more lumens per watt. Essentially, that means that an airport can use less energy to create the same levels of brightness. That can lead to significant savings on energy bills.
  
  
•  Lower carbon emissions
  Less energy means lower emissions. At a time when the vast majority of airports have a defined sustainability strategy, that means that higher CCT luminaires can help to support those wider environmental goals.
  
  
• Fewer fixtures
  The more efficient a luminaire is, the more brightness it provides per watt. In turn, that can mean that an airport requires fewer fixtures to achieve the same illumination levels. As well as reducing the overall cost, that can save on maintenance too.

Would you like to know more about CCTs, or have a specific question that’s not addressed here? Please get in touch!

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