CLC Human Centric Lighting & Wellness 2 — Questions and Answers
Question 1: Which photoreceptor cell in the human eye is primarily responsible for circadian photoentrainment?
- Rod cells
- Cone cells
- Intrinsically photosensitive retinal ganglion cells (ipRGCs) (Correct answer)
- Bipolar cells
Correct answer: Intrinsically photosensitive retinal ganglion cells (ipRGCs)
ipRGCs contain melanopsin and project to the suprachiasmatic nucleus (SCN), making them the primary drivers of circadian photoentrainment.
Question 2: What is the approximate peak sensitivity wavelength of the melanopsin photopigment?
- 480 nm (Correct answer)
- 555 nm
- 620 nm
- 440 nm
Correct answer: 480 nm
Melanopsin has a peak spectral sensitivity at approximately 480 nm, in the blue-cyan range of the visible spectrum.
Question 3: A hospital patient room is being designed for post-surgical recovery. Which daytime CCT range best supports alertness and circadian health?
- 2700K–3000K
- 3500K–4000K
- 5000K–6500K (Correct answer)
- 1800K–2200K
Correct answer: 5000K–6500K
Higher CCTs (5000K–6500K) provide more blue-enriched light that suppresses melatonin and promotes daytime alertness, supporting circadian health.
Question 4: Which metric is used by the WELL Building Standard to quantify the circadian stimulus potential of a lighting environment?
- Equivalent Melanopic Lux (EML) (Correct answer)
- Color Rendering Index (CRI)
- Unified Glare Rating (UGR)
- Daylight Factor (DF)
Correct answer: Equivalent Melanopic Lux (EML)
The WELL Building Standard uses Equivalent Melanopic Lux (EML) to measure the non-visual, circadian-effective component of a lighting environment.
Question 5: Evening exposure to high melanopic illuminance primarily causes which physiological effect?
- Early onset of melatonin secretion
- Phase delay of the circadian clock (Correct answer)
- Increased cortisol production the next morning
- Accelerated sleep pressure build-up
Correct answer: Phase delay of the circadian clock
Evening bright light exposure suppresses melatonin and shifts the circadian clock later, causing a phase delay.
Question 6: The Circadian Stimulus (CS) metric developed by the Lighting Research Center ranges from 0 to 1. A CS value of 0.3 represents what threshold?
- Onset of visual adaptation
- Threshold for 50% melatonin suppression after 1 hour (Correct answer)
- Maximum achievable alertness
- Minimum for color discrimination
Correct answer: Threshold for 50% melatonin suppression after 1 hour
A CS value of 0.3 corresponds to the threshold for approximately 50% nocturnal melatonin suppression after one hour of exposure.
Question 7: Which environmental factor, when combined with dynamic lighting, most effectively reinforces circadian entrainment in shift workers?
- Acoustic masking
- Temperature cycling synchronized with light
- Scheduled meal timing (Correct answer)
- Passive air circulation
Correct answer: Scheduled meal timing
Scheduled meal timing is a strong non-photic zeitgeber that, combined with dynamic lighting, powerfully reinforces circadian entrainment in shift workers.
CLC Human Centric Lighting & Wellness 2
Which photoreceptor cell in the human eye is primarily responsible for circadian photoentrainment?