IEQ  – Lighting and Circadian Rhythm

Indoor Environmental Quality (IEQ) is affected by many different factors. How light affects our health is in its nascent stages of being explored. Nevertheless, there exists enough evidence to know that artificial lighting can be a boon to one’s daily activities or can be detrimental to one’s health. Lighting and circadian rhythm have been shown to affect blood pleasure, heart rate variability, EEG results, melatonin production, and hormonal balance. These correspondingly affect mood, quality of sleep, alertness, and focus.

So in the built environment where one spends most of his or her time inside, how do we curate light that is good for our health and state of being?

IEQ & Lighting Design

An often overlooked aspect of sustainable design is advanced lighting and circadian rhythm control strategies. Lighting and circadian rhythm affect health and productivity. Light design is complex and there are knowledgeable people who specialize in it that can help. Nevertheless, in order to be empowered it is good to know the basics. There are many instances where lighting can be improved and the more you know the more empowered you are to affect change. Areas that are often ignored include offices and schools.

Indoor Environmental Quality IEQ – Lighting and Circadian Rhythm. Image courtesy of USAI lighting

Lighting Terminology

Some basic lighting terms to understand are CRI, Correlated Color Temperature, and brightness aka. lumens. These three components have a great effect on how a light source is perceived and consequently how it will affect the body.

CRI, abbreviated for Color Rendering Index, refers to a light source’s ability to reveal colors faithfully. It is based on a scale from 0 to 100. A CRI of 100 means that the light source is revealing the color spectrum in the same way that natural light would. The CRI rating is determined by using a radiating black body as a reference point. A black body is an opaque object that emits thermal radiation in the form of light. The higher the CRI the more the light source is able to reveal the full spectrum of light. The higher the CRI the more vibrant the color will seem. Low CRIs produce a washed out look. Whereas higher CRIs, such as those above 90, illuminate with greater accuracy.

Correlated Color Temperature (CCT) has to do with how the spectrum is modified to portray different shades of light. Similar to CRI, its reference point is also a radiating black body. When the black body is heated it will begin to change hue. A numerical value is assigned to the hue that is produced. Lower color temperatures such as 2200-2700K (Kelvin) produce warm colors like red, orange, and yellow, these temperatures are akin to the colors one sees when one looks at a sunset. Higher color temperatures in the 5000-6000K range produce a white/blue light that is akin to the light one experiences at high noon.

Brightness, measured in lumens is the light output a light source produces. A 60 -watt incandescent bulb has a brightness of 800 lumens. Natural light produces more lumens at some times than others. USAI’s helpful chart above shows how lumens and color temperature change over the course of the day. For instance, at dawn lumen levels are approximately 1700 whereas mid afternoon light produces an estimated 1900 lumens. A light source putting out higher lumens requires more current.

Lighting and Circadian Rhythm Studies

Studies have suggested that the beneficial effects of lighting are situation, task, and time dependent. Light can be complementary to our daily activities or it can add stress to them. The determining factors for a lighting design’s success is how closely it aligns with our circadian rhythm, also known as our internal clock, as well as how well we schedule our activities to fit into this rhythm. The three terms explained above contribute to how lighting design can mirror the passing of a 24-hour day. This is important because different types of light trigger different physiological affects. Blue/white light akin to bright midday light, suppresses melatonin and increases serotonin, this light is great for activity. Conversely red/orange light triggers melatonin in preparation for going to sleep. If everything is in balance the body will generate dopamine, serotonin, cortisol and melatonin in the right quantities at the right time of day. When circadian rhythms are off, a cascade of hormonal imbalances can result, leading to sleepless nights, poor concentration, irritation, stress, and illness.

Fortunately, companies and studies are exploring how dynamic lighting and circadian rhythm are intertwined – so intentional changes to color temperature and luminosity throughout the day can cater to both circadian rhythm and activity. For more research on this topic, please refer to USAI’s website, which lists a number of insightful studies having to do with lighting’s effect on circadian rhythms. The one titled “Lighting Affects Students’ Concentration Positively: Findings from Three Dutch Studies” is particularly compelling. Additionally, the company’s website provides useful charts that suggest different color temperature and intensity for different tasks done throughout the day.

Lighting and Circadian Rhythm Affects Students’ Concentration Positively:

Findings from Three Dutch Studies

The following study examines Light studies and circadian rhythms: