LIGHT- a Friend or Foe?

Day light or Artificial Light?


Recently I have been researching on the non-visual effects of lights (NVEL) and found some scary stuff which I had to share with my readers. However the findings are either theoretical or based on laboratory experiments, informed mostly from epidemiological researches. This post is a extract from of my academic research solely posted with an intention to make my readers aware of the devastating effects lights can create and possible ways to ameliorate them!

Natural day-night-cycle promotes human wellbeing. Daylight exposure is essential to conduct several physiological functions (Roberts 2010). However practically we spend 90% of the time indoors (SynthLight 2004) under static artificial illumination resulting in elongated days and poor day-night contrast (Blask et al 2012). This leads to disruption of human-circadian-rhythm. The finding that breast cancer incidence is highest in industrialized regions where night-light is ubiquitous directed the research of NVEL in buildings (Rea 2002). Considering that natural-lighting modulations are unavoidable within buildings it is necessary to study the NVEL on human-health to avert any negative effects.


Eye detects electromagnetic solar radiations in the range of 380-740nm (Thompson and Hill 2010) called visible radiation or light. Hitherto it was considered that brain receives signals (mostly visual) through ‘rods and cones’. During 1990’s third photoreceptor ‘Intrinsic photosensitive retinal ganglion cell (ipRGC)’was discovered (Graham 2011; Duffy and Czeisler 2009). ipRGC contains ‘melospin’ photo-pigment that conveys non-visual signals via ‘retinohypothalamic-path’ to ‘Suprachiasmatic-nuclei (SCN)’ located in brain. SCN is considered the ‘biological-clock’ and relays information to nervous system that regulates production of different neurohormones and neuropeptides mainly depending on the day-night-cycle and the timing of light-exposure (Roberts 2010).


Circadian-system controls daily and seasonal rhythms (CIE 2003; Roberts 2010; SynthLight 2004). Circadian-rhythm is endogenous. Natural-light aids entrainment of the human-clock which is between 24-25hrs to match with environmental-photoperiod (CIE 2003; Roberts 2010;Duffy and Czeisler 2009; Blask et al 2012; Cromie 1999) hence the presence of daylight or its equivalent within the building is essential for well-being.

Non-visual effects of lights (NVEL) on human-health

Although NVEL is relatively a new study and several areas are still dubious. It is confirmed that light-exposure differing environmental-photoperiod is detrimental to health. For example it causes cancer, cardiovascular disease, metabolic disorders, mental and emotional problems, sleep disorders, depression and mood disorders, gastrointestinal and digestive disorders, affects cognitive functions, immune system and reproductive functions (Blask et al 2012; Bommel 2006; CIE 2003; Circadian-rhythm (2013); Duffy and Czeisler 2009; Lynch 2008a; Morgia et al 2011; Portaluppi et al 2012; Rea 2002; Roberts 2010).

What affects Circadian-response?

Circadian-response is a slow cyclic process (Rea 2002; Blask et al 2012). Phase-shift (delay or advancement) of circadian-rhythm can easily occur if time and intensity of environmental-photoperiod is modified (CIE 2003; Rea 2002; Bieske et al 2012). Bright daylight and low or no nightlight benefits circadian-rhythm. Longer low-level day-time light-exposures due to limited daylight exposure or by use of energy-saving artificial-lighting can suppress melatonin (Rea 2002; Blask et al 2012) while early evening or nightlight-exposure also results in phase-delay (Anderen et al 2012). Constant time-change in light-dark patterns affects circadian-rhythm most (Roberts 2010; Webb 2006).

Such findings imply two things-importance of living in harmony with environmental-photoperiod and influential lighting parameters that affect circadian-response (LPCR). LPCR are interrelated. These include light spectrum, correlated color temperatures, intensity, direction and timing.

Morning daylight has blue-short-wavelength and entrains daily human-circadian-system (Figueiro and Rea 2010). Blue-wavelengths exposure is beneficial at day-time and harmful for night and the opposite is good for night-shift-workers (Roberts 2010). Roberts (2010) pointed at some artificial-lights like incandescent and fluorescent-light that have little or no irradiance at 480nm wavelength and hence safe for night-use. However this reading may be faulty since same lamp type may generate different spectrum reading based on how it is measured (Padfield no-date).

Daylight is uniform, diffused (Zilber 1993; Lynch 2008a; Altomonte 2008) and provides wide spectral irradiance strong at all visible wavelengths (Blask et al (2012). Most artificial-lights are dominated by wavelengths nearing 555nm (Figueiro and Rea 2010). It is hard to mimic natural-light quality even with full-spectrum artificial-light since they have spiky (fluorescent-light) or incremental monotonic irradiance (incandescent-light) wavelengths (Blask et al 2012)

Daylight can achieve best retinal-illumination as compared to artificial-lights (Altomonte 2008 ). Rea (2002); Bieske et al (2012); Roberts (2010) agree that direction of light has an important role in triggering circadian-response. However exact location of non-visual photoreceptors is still not known (CIE 2003).

Daylight is highly dynamic in illuminance as compared to indoor environment (Zilber 1993; CIBSE 2003; Blask et al 2012; Altomonte 2008). Duffy and Czeisler (2009) noted that day-time indoor-lighting is inadequate while Falchi et al (2011) noted that nightlight exposure in an urban setting with artificial-lighting is about 200 times higher compared to environmental-photoperiod, both of which are detrimental to health.

A wide range of illuminance (0.2lux-1000lux) is capable to trigger circadian-response (Bommel 2006; Circadian-rhythm 2013; Rea 2002; Falchi et al 2011; Duffy and Czeisler 2009; Blask et al 2012). Rea (2002) showed time progression also affects sensitivity to nightlight.

Selecting appropriate lights:

Daylight is a sure winner as far as ameliorating NVEL is concerned. Surveys endorse sunlight as a preferred light-source (Lynch 2008a). Benefits of using daylight include substantial energy-saving, low-carbon-emissions, improvement in mood, motivation and productivity (Kjeld Johnsen no-date; Lynch 2008a; SynthLight 2004; Bommel 2006). Daylight in buildings however must be balanced with its visual-effects like uniformity, glare and heat gain. However it is not always possible to use daylight.

Global artificial-light use still comprises of 67% high-energy-consuming incandescent-lamps versus 33% energy-savers within which housing consumes 75% of incandescent-lamps (The Climate group no-date). Compact-fluorescent-lamps and Light-emitting-diodes are thrust globally to reduce energy use and carbon emissions. However these have not been carefully evaluated for NVEL. The research on NVEL is still ongoing and applying partial knowledge can deem incorrect but so is our knowledge of using energy-efficient lamps (for their non-visual effects).

Summary: Lighting aids vision but it can also prove detrimental to human-health if NVEL are ignored. Living in harmony with environmental-photoperiod may leave the circadian-system intact. Daylight is most preferred. Selection of complementary artificial-lights needs consideration of NVEL. The study of NVEL is of special interest while designing spaces for night-shift workers or for people with special needs. Hence application of above learning must result in situational lighting design.