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Daylight vs Artificial Light

I mention that 300 lux of artificial lighting was not equal to 300 lux daylight. Here are some of the arguments

to substantiate the case. Daylight has a better light quality than electric lighting.

Light quality is a holistic term which includes attributes like light distribution, colour rendition, flicker,

sparkle, variability and influence on circadian photobiology.

Distribution of light

Daylight in diffused form tends to illuminate surfaces more evenly in all directions. Electric lighting typically

illuminates in a certain direction e.g. horizontal or vertical plane. In other words surfaces are more brightly lit

either in the horizontal or the vertical plane. Daylight tends to illuminate both horizontal and vertical surfaces

more evenly, thus, the roof, the walls and the floor look more evenly lit. Therefore, daylight in diffused form

offers better sense of space.

Discriminating colour

Colours look more natural in daylight than under electrical lighting, as electric light sources are stronger in

some areas of the light spectrum and weaker in others. The human eyes ability to discriminate colours is

dependent on the spectral content of light, and daylight contains light of almost all visible wavelengths,whereas most electric lamps emit most of their light over a limited wavelength range. Daylight thus has a

continuous spectrum and therefore provides better colour rendition. Colours tend to look more vivid in

daylight. It may be added that under daylight human eye can differentiate between 500 000 yes, half a million

different shades, while under normal fluorescent lighting the corresponding figure is 8, yes eight.

Flicker

Daylight does not flicker; fluorescent lights can have a noticeable flicker. People blame this for a multitude of

problems like headache, eye strain and attention deficit problems. Fluorescent lights than run on electronic

ballasts have considerably reduced flicker problems, but only daylight guarantees a total absence of flicker.

SparkleSparkle or highlighting three dimensional objects is enhanced by daylight.

This makes objects more attractive and easier and quicker to understand three dimensionally.

Variability

The inherent variability of daylight as clouds move through the sky, successively obscuring and revealing the

sun. Some studies have shown that this variability of daylight has relaxing effect on the eyes (Sze-Hui Au,

Leony (1999), Innovative lighting systems, Cardiff University: Honours Thesis).

Motivation

Research has shown that people experiencing positive emotional states tend to be more productive (Wright,

TA and Cropanzano, R. (2000). Psychological well-being and job satisfaction as predictors of jobperformance. Journal of Occupational Health), and that positive emotional states can be reinforced by

providing people with their preferred work environment. Since daylight is almost universally preferred to

electric lighting, it is likely that increased use of daylight will support workplace productivity.

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In a study (Figueiro, M.G., Rea, M.S., Stevens, R.G., and Rea, A.C. (2002) Daylight and productivity - a

possible link to circadian regulation, Proceedings of the Fifth Intl LRO Lighting Research Symposium, EPRI:

Palo Alto, CA.) it was found that workers in windowless offices spend a small but statistically significantly

greater amount of time talking to others, either directly or by telephone; and a small but statistically

significantly lesser amount of time working on their computer, relative to the workers in the windowed

offices. It was hypothesized that the people in the windowless offices would not receive sufficient light to

entrain their circadian systems and so would seek to entrain them either by seeking out

exposure to daylight and consequently spending less time in their offices, or by seeking more socialinteractions, a factor that can also be used to entrain the circadian system. An alternative explanation for

these findings would be that the workers in the windowless offices were seeking additional

short-term stimulation, something that was provided by the view out in the windowed offices, and the

differences in behaviour had nothing to do with the circadian system. Regardless of which explanation is

correct, the presence of a window would seem to provide a benefit in terms of desirable behaviour at work.

Preference for daylight

There is no doubt that people find daylight more pleasant than electric lighting as their primary source of

light. Wells (1967), Manning (1967), and Markus (1967) in the UK; Cuttle (1983) in the UK and New

Zealand; Heerwagen and Heerwagen (1986) in the USA; and Veitch (1993) in Canada, have all shown

that high percentages of survey respondents prefer to work by daylight.Similarly, people prefer to sit at desks that are beside windows rather than further back in the room,

especially when those windows have access to direct sunlight (Markus, 1967; Aldworth and Bridgers, 1971;

Collins, 1975; Ludlow, 1976; Cuttle, 1983; and Heerwagen and Heerwagen, 1986).

Mood and satisfaction

Dasgupta (2003) found a small but statistically significant reduction in negative mood for people who worked

for about 20 minutes in a private office with a large window during daytime; but no reduction in negative

mood for the same people in the same office at night. Ruys (1970) also found that occupants of small offices

disliked the absence of windows.

Some studies have suggested that people have an innate desire to be in contact with nature White andHeerwagen, (1998); windows provide a means for establishing visual contract with nature while at work.

Heerwagen and Orians (1986) found that people occupying small windowless offices were much more likely

to have pictures of natural scenes on their wall than were people with easy access to windows, possibly as a

way of compensating for the absence of real natural scenes. An alternative explanation is that, in a small

office, the view out the window may be the only source of environmental stimulation.

Circadian photobiology

A study (Rea, MS, Figueiro, MG, Bullough, JD, Circadian photobiology: An emerging framework for

lighting practice and research, (2002) Lighting Research and Technology 34(3), 177-190.) Lighting can be

used to strengthen the human circadian rhythm, which determines various physiological functions such as

sleep, digestion, alertness, depression, and probably general health. Daylight is much more effective than

electric lighting at entraining the circadian system; this is because the circadian system responds only to

high levels of blue light, such as those found in daylight. Rea et al. calculate circadian efficacies for various

light sources, and find that daylight is three to four times more effective than fluorescent lamps, and twenty

times more effective than incandescent lamps.

They find that ''light levels approaching those found outdoors in daylight are sufficient for regulation of the

circadian clock and the melatonin cycle, but many indoor light levels are too low.

Kalle Hashmi