Earthlight

The Science

Your building runs on light. So does everyone in it.

Light is not decoration — it is the primary signal your occupants’ biology reads to keep time. The evidence is peer-reviewed and measurable. Earthlight turns it into a case your board can defend.

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01 — The mechanism

How light becomes biology

For two decades, science thought the eye had two photoreceptors. It has three — and the third one isn’t for seeing. It’s for keeping time.

A third photoreceptor

Beyond the rods and cones you see with, the eye carries intrinsically photosensitive retinal ganglion cells — ipRGCs, discovered through the melanopsin pigment in 1998–2002. They don't build images. Their job is to tell the brain what time of day it is.[1][2]

Wired to the master clock

ipRGCs run straight to the suprachiasmatic nucleus, the body's central clock, which synchronizes sleep, hormones, metabolism, and alertness to the day. They are most sensitive to blue light near 480 nm — the signature of open sky.[3][4]

Light sets the clock — or disrupts it

Bright morning light advances and steadies the clock; light late in the evening delays it and suppresses melatonin. Even ordinary room light (~200 lux) can blunt melatonin in most people. Timing, intensity, and spectrum are the signal.[5][6][7]

Daylight runs 10,000 to 100,000 lux. Most interiors run 100 to 500. To your biology, an ordinary office is closer to dusk than to day — all day.

02 — The evidence

What the studies actually show

We don’t cherry-pick. The strongest evidence sits in longer-stay and recovery settings; acute-ICU trials have been mixed. Naming the limits is exactly what makes the rest defensible.

−22%post-surgical pain medication

Spinal-surgery patients on the sunnier side of the same ward — 46% more daylight — used 22% less analgesic per hour and had 21% lower drug costs.[8]

Prospective study, n=89

+46 minsleep per night

Office workers with window daylight exposure slept 46 minutes longer and reported better sleep quality than those in windowless offices.[9]

Pilot study, n=49

RCTdementia care

In a 3.5-year randomized trial, all-day bright light slowed cognitive decline ~5% and cut depressive symptoms 19%; paired with evening melatonin it reduced aggression 9%.[10]

Double-blind RCT, n=189

Group 2Athe cost of disruption

The WHO's cancer agency classifies night-shift work involving circadian disruption as “probably carcinogenic.” Sleep-disrupted hospital staff make 36% more serious errors — the stakes of getting light wrong.[11][12]

IARC Monograph 124; NEJM RCT

03 — The standards

The science has been standardized

This is no longer emerging opinion. The field now measures circadian light in melanopic EDI — a melanopsin-weighted metric formalized by the CIE. In 2022, a consensus of the leading circadian scientists set indoor targets: at least 250 melanopic EDI during the day, under 10 in the evening, and near 1 at night.[13][14]

WELL, the IES, UL, and Fitwel have each translated the research into design guidance. The evidence is settled enough to specify against — and, just as importantly, to model.

Grounded inCIE S 026 ↗WELL v2 · L03 ↗IES RP-46 / TM-18 ↗UL DG 24480 ↗Fitwel ↗

Put the evidence to work.

An independent, on-site lighting assessment turns this science into a Facility Report your board can act on — before the specification is written.

See the lighting assessment →Book a 20-minute conversation →

Sources

  1. [1]Provencio I, et al. Melanopsin: an opsin in melanophores, brain, and eye. PNAS, 1998; and A novel human opsin in the inner retina. J Neurosci, 2000.
  2. [2]Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science, 2002.
  3. [3]Hattar S, et al. Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity. Science, 2002.
  4. [4]Brainard GC, et al. Action spectrum for melatonin regulation in humans. J Neurosci, 2001 (peak sensitivity ~464 nm).
  5. [5]Khalsa SBS, Jewett ME, Cajochen C, Czeisler CA. A phase response curve to single bright light pulses in human subjects. J Physiol, 2003.
  6. [6]Lewy AJ, et al. Light suppresses melatonin secretion in humans. Science, 1980.
  7. [7]Gooley JJ, et al. Exposure to room light before bedtime suppresses melatonin onset. J Clin Endocrinol Metab, 2011.
  8. [8]Walch JM, et al. The effect of sunlight on postoperative analgesic medication use. Psychosomatic Medicine, 2005.
  9. [9]Boubekri M, et al. Impact of windows and daylight exposure on sleep quality of office workers. J Clin Sleep Med, 2014 (pilot).
  10. [10]Riemersma-van der Lek RF, et al. Effect of bright light and melatonin on cognitive and noncognitive function in elderly residents. JAMA, 2008.
  11. [11]IARC/WHO. Night shift work classified Group 2A, “probably carcinogenic.” Monographs Vol. 124, 2019 (first classified 2007).
  12. [12]Landrigan CP, et al. Effect of reducing interns’ work hours on serious medical errors in ICUs. NEJM, 2004 (a schedule study, establishing the cost of circadian disruption).
  13. [13]Brown TM, et al. Recommendations for daytime, evening, and nighttime indoor light exposure. PLOS Biology, 2022 (≥250 melanopic EDI day; ≤10 evening; ≤1 night).
  14. [14]CIE S 026:2018 — the metrology standard defining melanopic Equivalent Daylight Illuminance (melanopic EDI).

Effect sizes are drawn from the cited peer-reviewed literature and reflect the conditions of each study; they are not guarantees of outcomes in any specific building. Earthlight’s Facility Report models a defensible range for your site from its measured conditions.