When meeting with customers to look at their lighting, I occasionally hear the phrase, “It is too bright over there.” When I hear this, I often follow up with the question, “Can you explain what you mean by 'too bright'? Do you feel you have too much light or is the light ‘too’ white?”
The answers always vary. Sometimes a customer is referring to the quantity of light that is needed or not needed, other times a light source is causing too much glare, and many times, the customer just doesn't like the color temperature of the light.
How Does Traditional Color Temperature Translate for LED?
Color temperature in lighting refers to the tone of “white” light that is emitted from a light source.
An easy way to think about it is to think of all the shades of white a T-shirt may go through in its life. Wash it with your dark blues and the white T-shirt still looks white on its own, but put it up to a new shirt and it may look slightly blue. Wear a T-shirt too long, and when you set it next to a new shirt, you realize the old one is now yellow. White light also looks very different when two different sources with two different color temperatures are put side by side.
In order to differentiate the various hues of white, artificial light sources are labeled with either a color temperature (incandescent and tungsten halogen) or a correlated color temperature (CCT) (nearly everything else). Both color temperature and CCT are measured in degrees Kelvin, derived from “blackbody radiation”.*
Simply put, as an idealized blackbody absorbs radiation, it glows different colors. At a temperature of 2000K, it is a very orange-yellow color. As the temperature increases, the color shifts to yellow, yellowish white, white and then a bluish white.
So in the lighting world, the color of white has traditionally been classified as warm white or cool white, depending on its CCT. When our lighting sources were more limited and LED was not a commercially available item, incandescent, halogen, and fluorescent with a CCT of 2700K or 3000K were known as “warm white”. Fluorescents with a CCT of 3500K were called “neutral” and any source with a CCT of 4100K and above were considered “cool white”.
LEDs have changed that. When LEDs first became commercially viable in “white”, they were least expensive in the bluer spectrum, so nearly all of the early “white” light sources leaned toward a CCT of 6000K and above. Because of that, we now see manufacturers calling 5000K neutral, and I've even seen some call 4000K “warm white”.
That said, the most important tip I can give to LED buyers is to ask what the correlated color temperature of a lamp or fixture is before purchasing it, not whether the color temperature is “warm” or “cool”.
Another very important note is that correlated color temperatures have a chromaticity range. Without going into scientific detail, to an installer and end user, that means that not all 2700K CCT lamps will look the same. So to avoid any issues, it is best not to mix and match manufacturers unless you have tested their products with each other.
Why is Understanding CCT Important?
The reason CCT is important is because of the way light makes a space feel.
Candlelight ranges from 1500–2000K, and to most people it is romantic-feeling. Thus restaurants, hotels, and homeowners who want a cozy feel may want to look toward color temperatures that are 2400–2700K. Transitional spaces moving from cozy to a more productive space (like hallways) may opt for color temperatures in the 3000–3500K range.
Warm CCTs also draw out the warm colors in furniture, art and other objects in the space. So designers will usually recommend 2700–3000K if you want to highlight the reds and yellows in the wood grain of your flooring.
On the other hand, I am seeing a lot of commercial and industrial facilities trending toward 4000–5000K sources because the light more closely matches daylight, and they feel it makes a space “feel” more productive and business-focused.
The other advantage to cooler light is that often people perceive it as “brighter” or producing more light than a source with a warmer color temperature. Because of this increase in perceived light, shifting to cooler color temperatures may also have an energy-saving effect for some businesses, as they can actually use less light than they could with warmer CCT sources.
Understand Your Objective for Lighting in Every Environment
There are pros and cons to both warm and cool color temperatures. The key is understanding the environment you are putting the lights into.
Warm colors can be perceived as “not bright enough” if they are used in an area where people want crisp white light to work under. In areas where naturally cool-colored daylight enters from windows and skylights, warm colors tend to look more yellow or pink, so people may think the lights aren't working properly.
The potential downside of using cool colors is that many people perceive it to be “institutional” or “sterile”. People may complain that their lighting is “too bright” if you change from a warm color to a cool color, even if the measured light output remains the same or decreases slightly.
Evaluating the needs of your environment is key to picking the right color temperature.
Make sure you tell your supplier what type of environment or what type of ambience you are looking to create in a space. Also, if you plan on shifting from one light source to another (fluorescent to LED), or changing the CCT, my recommendation would be to finish entire rooms at the same time. Just like the analogy with the T-shirt, if people don't see two different CCT light sources near each other, it is harder to notice a difference.