January 21, 2017 – This topic has been getting a lot of attention for the last 10 years, initially in Europe and now increasingly in the US. It’s a complex topic, so newspaper articles and even policy statements by such notable organizations as the American Medical Association tend to oversimplify the topic. This can lead to generalizations that may not be true. Here’s some examples of what we do and don’t know.
Visual human effects from the color temperature of light have been recognized for a long time, and are partly related to personal preference and partly a result of the intense human visual stimulus to very bright, bluish-white light. Conversely, warm colored light combined with good contrast in an interior environment puts us in a relaxed mood.
For most of our experience, this preference determined what color temperature of light was specified. Warm light from a low 2700°Kelvin (K) has been typical for incandescent, compact fluorescent, and now LED screw base lamps. Most office and academic work environments use a mid-range color temperature between 3500 to 4100° K. Industrial and medical surgical applications frequently use 4000 to 6500° K.
Now, researchers at a range of institutions from Rensselaer’s Lighting Research Center to the Danish Company Chromaviso are demonstrating how the spectral content, ie, the range of colors in the spectrum that make up light color, and the intensity of light can alter biological processes. Studies have so far shown conclusively that blue-rich white light, even at low light intensity, can suppress the sleep-related hormone melatonin. The potential negative impact to normal circadian rhythm of exposure at night are often related to the late evening use of smart phones and computers, but the same blue-rich white light can be beneficial to circadian rhythm cycles when exposure is at a high level of intensity in the late morning.
Not only is the time of exposure important, but the effect of such light can be more pronounced, and beneficial, to people of different ages. Researchers have recognized a positive effect of a blue (570 nanometer spectrum) light presented in direct view for a limited amount of time after dinner to patients with Alzheimers Disease. It helps to normalize sleep patterns in these patients who are prone to wakeful night wandering.
In schools, it is well known that children have a harder time waking up in the morning than adults. Bright white light can have a beneficial effect on attentiveness in morning classes as well as during the early to mid afternoon slump. However, very bright-white light can also exacerbate hyperactivity in children, and may lead to higher stress levels for teachers who appreciate the calming visual effect of warmer light.
As you probably are concluding, bright-white light is better in some situations than others, and warm, lower level light can be beneficial in others. This is the general idea of “human-centric lighting” which posits that using the variability of LED light sources, we can design lighting systems that flexibly allow the right color and intensity of light for a specific application and use of a space at any given time. Time is an important changing variable in the equation. What if we can simulate the changing color temperature of daylight throughout the day. Would changing the color of LED lighting in a space provide the same benefits as daylighting in locations where you don’t get good natural daylight for many months of the year?
To determine the right color and quantity of light to use, you must first understand the building owner’s requirements and expectations. This is accomplished as part of the commissioning process, through the development of the Owners Project Requirements (OPR). The OPR includes information about the building occupants, tasks and visual needs, daylighting access, aesthetics, energy use targets, maintenance staff capability, controls technology, applicable codes and standards, LEED certification, and many other issues.