The lighting industry today is becoming saturated with talk of numerous new technologies, how they will enhance our lives in passive ways, and why we should buy into the hype. One such technology being pushed is selectable color temperature – the ability to program interior lighting fixtures to mimic the way the sun goes from a warm red in the morning to a cooler blue in the middle of the day and back to the warm red at sunset. Research dollars are being spent to better understand our circadian rhythms and how lighting affects these natural flows; marketing dollars are in turn being spent to tell us that it’s all about the lighting.
The questions being asked, and the answers they provide, will impact the generations to come. How has the shift to cooler fluorescent interior lighting affected our well-being? Is there a better way to light our interior spaces? Where should we be mimicking nature in order to regulate our natural rhythms? What are the lighting design best practices for well-being?
First let us dispel some potential confusion. There are two types of adjustable color temperature LEDs on the market today: those that shift to the lower temperatures when you dim, referred to as “warm glow” or “warm dim,” and those that are adjustable at any intensity, which are referred to as “selectable color temperature.” The difference comes down to complexity. Do you want your LEDs to dim in a fashion similar to what you experienced with incandescent lights without having to worry about more nobs and dials? If so, pick a warm dim LED. However, if you want complete control over when the light is warm and when the light is cool, add a second dimmer or control module and go with the selectable color temperature.
Why is this even a thing?
The most efficient LEDs, in terms of lumens per watt, are a solid blue. Over the past few decades, manufacturers have been creating ways to adjust this color to emit more white through the addition of phosphors. However, when you add this layer of phosphor, the amount of light that comes out of the LED decreases. The balance has always been adding just enough to get the right color.
Incandescents were created and function in an entirely different capacity. They take a current and pass it through a thin metal string, called a filament, which glows as it heats up to produce light. When we reduce the current being sent through this metal its glow dims but, as with all fires, this dim fades towards the red spectrum.
This is one of the fundamental disconnects between LED and incandescent lights. Dim an LED and the light temperature remains constant. Dim an incandescent and you get this nice rich, red glow. Manufacturers wanted the efficiencies of LEDs, but didn’t want to give up this feature, so they created selectable color temperature lighting.
How it works
An LED light fixture typically comprises multiple LEDs on a single board. The light from these LEDs is usually mixed either with a lens or with a remote phosphor – or through the lighting fixture construction – to soften the individual pinpoints of light. To produce selectable color temperature lighting, manufacturers have added two or more colors of LEDs onto a single board. For example, cool and warm light. Then, depending on the requested temperature, one set of colors dims as the other set intensifies in order for the mix of the two colors to produce the requested temperature.
This method doesn’t come without its drawbacks. The first limitation is light output. Twice the number of LEDs are required on a board in order to allow the range of options, with one group either completely off or the two groups dimmed in such a way that the light’s intensity doesn’t fluctuate. Another limitation is a loss of efficiency. The lower color temperature lighting requires more phosphor, leading to less lumens out per watt. Finally, there is an increase of control complexity, with each control station requiring two dimmer switches: one for color and one for intensity.
Where they should be used
I have had clients ask for LEDs to be retrofitted into their existing spaces, only to come to hate the cold feel the LEDs provide. When I hear this feedback, it is really the clients commenting on how they enjoyed the warmer temperatures when the lights were dimmed. Warm dim or selectable color temperature should be used where a client desires to maintain that ‘incandescent’ feel and doesn’t mind spending a few additional dollars on their electric bill.
Another application for selectable color temperature is where specific colors must be created, such as when highlighting a business logo or displaying clothing or fabrics for sale. The eye sees colors differently depending on the conditions, such as source lighting, which provides flexibility in the commissioning of these highlight lighting fixtures to avoid any future headaches. Dialing in the color temperature to get that exact shade of red can be very satisfying. Note that selecting a lighting fixture with a high color rendering index (CRI) improves how all colors will look and should be seriously considered when used in this application.
Lastly, selectable color temperature can be used in spaces where human productivity and well-being is of the highest priority. Hospitals, care facilities, even office space with an aligning corporate culture are ideal areas to upgrade the lighting package and dial in the specific color temperatures. Commissioning is important in these applications. If the shifts in color temperature are fixed throughout the day, such as to mimic the outdoor environment, they should be programmed properly to get the most out of the system. If the client wishes to tweak the settings, training is a must so that they use the system properly – now and in the future.
Selectable color temperature lighting fixtures are important tools for a lighting designer but should be used for the proper application. When they are combined with natural daylight, holistic facility management strategies, and functional lighting design, they can transform our interior spaces into comfortable, healthy environments for all.