3 circadian design models... from a global perspective

Numerous scientific studies show that the human circadian rhythm is, on average, 24.2 hours. But the earth rotates every 24.0 hours.

It turns out that the only factor that synchronizes (entrains) our rhythm to the earth rotation is bright light during the morning. Without this signal, our sleep quality "wanders", and our immune system is negatively impacted.

Before the 1970s, we used to have a design goal of indoor light achieving 1000 lumens. With the energy crisis we needed to reduce our energy consumption. As a result we lowered the goal of indoor lighting to 350–500 lumens. It turns out that that is too low. We need to increase the signal of "bright days" entering the eye during the morning to return us to the system that we evolved within. We also need to design for "dim nights" during the evening.

What is the impact of not delivering the bright days and dim nights? We are seeing lower alertness during the day. There is also increased incidence of diabetes, depression, cardiovascular disease, and even cancer.

How much is enough?

When it comes to selecting a lighting approach to achieve a health goal, designing for bright days and dim nights just got much easier.

What are the three design approaches?

Lighting industry experts were convened by three lighting bodies to author a design approach so that the lighting industry could deliver circadian effective spaces. Those three bodies were:

• WELL Building Standard, based on Equivalent Melanopic Lux (EML)
• UL Design Guideline 24480, based on Circadian Stimulus (CS)
• DIN/Tech Specification 67760, based on Melanopic-Equivalent Daylight Illuminance (M-EDI)

I had the honor to participate in one of those task forces, the Underwriters Laboratories process.

I learned some things that might be important for you to consider.

#1 All luminaires contribute to circadian effectiveness
In most scenarios even a fixed CCT luminaire can be used to deliver a circadian lighting goal. While I could argue that even candles could, theoretically, achieve the desired goals, the thought of trying to remove the heat from the candles is too difficult to imagine.

But let's look at the published design goals.

In both the WELL Standard and in the UL Design Guideline 24480, this is the case.  The goal is defined by the light hitting the vertical plane of the building occupant's eyes. The amount, the wavelengths (SPD), and the timing are important factors.

The one place where this can be argued is in the European approach defined in DIN/TS 67600. The claim made is that one needs to keep the lux levels in a space constant, even into the evening. This was based on the standard that some say was in existence "before" (even though I can't find it). To maintain the lighting levels and not deliver too much melatonin-reducing light (strong in the 490nm range), one has to use white tunable lighting. The reason for this is that  when the system needs to supply the signal for "bright mornings", one dials in the higher CCTs (more blue light). When the system needs to deliver the same lighting levels at night, one dials in the lower CCTs (more warm light).

While I have argued that this makes the need for a larger budget to accomodate the white tunable luminaires with appropriate controls, I get a strange smile. It makes me wonder.

#2 Ask your client if they have a preference
To meet your customer's needs, ask them if they have a preference. Perhaps the building owner relies on getting WELL Building points to achieve a higher score (Silver, Gold or Platinum). Or your client may rely on UL DG 24480 for circadian effective designs. In just one example, the General Services Administration (GSA) has a P100 document that defines the building system goals.

#3 Know your document's approach
Knowing the document that your using to design by is critical to being able to deliver on the goal. If you have questions, there are plenty of people you can contact to find out more. Circadian Lighting Advisors is just one of your options.

#4 Design your lighting system understanding that for 2–4 hours, you are going to deliver more lighting

Because the process to calculate the required lighting levels is not taught in schools yet, here is where you are going to need an experienced circadian lighting designer. 

#5 What happens after you designed the perfect project

After you deliver the designs to the customer, they often hand the lighting schedule to their contractor. The general contractor is often "in charge" of delivering the quality of the final project. In some cases, there is pressure to lower the price of the project (or increase profit margins).

This can be due to many issues, but imagine that a project for a new building is 3,175 steps, starting with locating the project, getting permits, digging the hole, and pouring the foundation. Now consider that by the time the lights are ready to be purchased and installed, you might be in the 3,055th step, after putting up the dry wall. At this point the project might have gone over budget on schedule and costs, and maybe lighting is one of those things that the contractor can save money on luminaires and controls.

If the last 5 projects you delivered were "value-engineered" (VEd is the term used by contractors and distributors), then there is still some work to do.

To ensure that the building occupants are receiving the benefits of the circadian design process, your job is not necessarily over when you hand off your designs. Your building owner has to involve you in the build out of the project so that you are in contact with the trades that take over the project.

In another blog post, I'll cover what happens when the customer pays for circadian lighting, but the project does not achieve the desired goals due to value engineering.