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Effects of Light on Humans – This survey of the complex effects of light on human biology and physiology, by Joseph Brennan of Dublin Institute of Technology, won the ILE’s ‘Best Written Paper’ award in the Society of Light & Lighting Young Lighters of the Year 2007. This is an abridged version of the original paper.

Introduction
The right artificial lighting design for a working/living/learning environment can not be determined by illuminance levels alone. Humans are complex physiological beings who respond to their environment. Without the optimum lighting environment we can not operate as efficiently as possible — lighting conditions can affect our well-being and productivity. While lighting designers and engineers are constantly urged to reduce energy and limit CO2 emissions, this would be counter-productive if it had a detrimental affect on the ergonomics of the end user’s environment.

1.1 The Eye
The eye is a complex organ and is responsible for regulating more biological functions than is commonly known. In addition to enabling humans to see, it is also regulates our internal body clock. This section offers a very simplified account of the key parts of the eye which play a role in our overall sight and well-being.

1.1.1 The Visual System
This organ shapes our perception of reality. Without it, lux levels, colour temperature and colour rendering would be meaningless words. It is common knowledge that we use our eyes to see the world around us, but their other functions are not commonly recognised. To understand this we must look at the biology of the eye.

Fig. 1.2 shows how the light enters the eye through the cornea, is limited by the pupil and focused by the lens onto the retina at the back of the eye.

As Fig 1.3 shows, the retina is divided into three groups: a layer of photo-receptors, a layer of collector cells and a layer of ganglions. Light filters through the layers of ganglions and collector cells and is absorbed by the layer of photo-receptors.

The photo-receptors are divided into two groups: cones and rods. All the rod receptors are the same and are distributed over the surface of the retina. The rods work best in low level lighting and do not determine colour. Cones are divided up into three groups: short wave (S), medium wave (M) and long wave (L), according to the wavelengths they are most sensitive to. The cones are mostly concentrated in the area of the eye called the fovea (Fig. 1.2). These cones determine colour rather like a projector in reverse – in other words the S, M and L cones are sensitive to different radiation levels in the light spectrum and dissect the colour and transmit the electrical discharges to the visual cortex.

Light is absorbed by the photo-receptors and converted into electrical signals, which are then transmitted to the visual cortex of the brain for processing.

1.1.2 The Circadian System
Circadian rhythms occur naturally in the human body over a 24-hour period and regulate body temperature, alertness, secretion of hormones like melatonin (which regulates sleep patterns) and cortisol (which regulates stress levels). Our circadian clock (biological clock) is located in

the suprachiasmatic nucleus (SCN) in the brain and is synchronised by light transmitted through the eye to the circadian system. (Brainard and Bernecker, 1995)

Like the visual system the circadian system’s point of influence is through the eye. In 2003, Peter Boyce wrote ‘The photo-receptor, or photo-receptors, used to influence the human circadian system have not yet been identified until now’. Recent research has shown that about 3% of the ganglion cells, mentioned earlier, contain a photo-pigment called melaopsin (David Berson, 2002). These nerve cells pass light messages directly to the hypothalamus and from there to the pineal gland, inhibiting the secretion of melatonin.

Light enters the eye and is absorbed by the photo-receptors in the ganglion cells and is converted into electrical discharges which are transmitted through the retinahypothalamic tract (RHT) to the SCN and then, by way of the paraventricular nucleus (PVN) and the superior cervical ganglion, to the pineal gland (Boyce, 2003). This route is called the Retinahypothalamic-pineal axis (RHP axis) — shown in Fig 1.5.

The pineal gland is where melatonin is secreted during periods when insufficient light reaches the eye – principally at night. Melatonin can be thought of as a messenger hormone. Melatonin detectors have been found throughout the body and melatonin itself has the purpose of transmitting messages from the SCN (the master clock) to these parts of the body to synchronise their physiological functions to start at their appropriate time in the 24-hour period (Cagnacci et al., 1997b). It is important that these hormones hit their targets on time to create healthy circadian rhythms.

It is not enough for light to be present to suppress the secretion of melatonin effectively. ‘Brainard et al. found that radiation at 505nm was four times as effective in suppressing melatonin as radiation at 555nm’ (Boyce 2003). It can be seen in Fig. 1.6 that radiation peaks at this level in natural daylight.

Humans need to receive this radiation during the day to suppress melatonin. However, for humans working in artificial environments, such as offices, where access to direct daylight may be limited, melatonin levels may not be suppressed sufficiently. This will affect the rhythms of the circadian system.

In some cases, the effect on the circadian rhythm and the circannual rhythms (yearly cycles) may be even more severe. Seasonally Affected Disorder (SAD) occurs as a symptom of these disruptions in circadian rhythms and manifests itself as depression, lack of libido, difficulty using problem-solving skills, insomnia and irritability. Light therapy has proven very effective in combating these forms of depression (Rosenthal et al., 1985; Kasper et al., 1989; Terman et al., 1989; Tam et al., 1995). People undergoing light therapy are exposed to high levels of light for short periods of time (e.g. 10,000 lux for 30 minutes). This has the effect or re-setting their circadian clocks. Milder forms of SAD are commonly referred to as the ‘winter blues’ and are thought to affect 13-18% of the North American population (Hill, 1992; Kasper, Rogers, Yancey, Skwerer, Schulz and Rosenthal, 1989). The number of cases has been shown to increase with latitude (Wehr and Rosenthal, 1989; Kasper et al 1989b).

However, is it a good idea to suppress the secretion of melatonin altogether during the day? ‘Bright artificial light, in excess of 2500lux, blocks the production of melatonin. Consequently, it awakens the organism and increases body temperature, which influences, in turn, our efficiency – especially when performing tasks that require complex cognitive activity. These effects, which are positive over the short run, can become a source of stress when prolonged.’ (iGuzzini,2006)

1.2 Alertness

It is a problem to keep office workers alert and focused — but in an industrial environment it is crucial. Many studies have been carried out on shift workers at night, where workers are fighting against their own biology. It was found that bright light has a direct effect on the alertness of workers. Fig 1.7 shows that over a test period the arousal level of two groups of workers fell steadily but the subject exposed to the brighter levels of light still had a significantly higher arousal level at the end of the test period.

Alertness is not only of key importance to mood and productivity but also to the accident rate. An increase in lighting levels reduces the likelihood of accidents. This can be seen in the graph in Fig 1.8. It shows a general decline in the accident rate with the increase of illuminance. The survey of 347 accidents in an industrial environment in 1995 was conducted by Volker, Ruschenschmidt and Gall.

1.3 Productivity

Many factors, such as skill, education and previous experience can affect productivity. However, lighting is one of the least expensive and the most important influences on human performance in the work environment (Katzev, 1992). It has also been shown that an increase in lighting levels can not only increase alertness, thus reducing accidents, but that lighting has a direct effect on the mental and physical health of humans. This section will demonstrate how increases in lighting levels can improve visual performance, accuracy and production speed.

The level of lighting has to be sufficient to allow the user to perform the visual task with as little effort as possible. Required task lighting levels will depend on the user’s age and degree of visual impairment. Fig 1.9 shows the relationship between age and lighting requirement for reading good print (Fortuin, 1951) and Fig 1.10 shows the lens transmittance within the eye for various age categories. The values are expressed as a % of the 560nm point for a new born baby (adapted from Brainard et al 2001).

It is evident from Figs. 1.9 and 1.10 that age has a bearing on visual ability, with older users requiring more light to perform the same tasks as accurately as younger users. Fig 1.11 (taken from the CIE) shows that to have the same visual performance as a younger person at 300 lux an older person would need approximately 2000 lux.

Providing workers with sufficient light to perform visual tasks improves their accuracy, thus increasing production speed and reducing wasted materials/production time. The key is to take the age of the end users into account and design to their lighting requirements.

As Handbuch fur Beleuchtung illustrates, in Fig 1.12, an increase in lux levels in an industrial environment has a direct effect on the production levels achieved. These results are based on a cross section of workers in these industries, to give unbiased results.

According to Van den Beld and van Bommel (2001), increasing the lighting from the required 300 lux to 500 lux leads to an increase in productivity of 10-25% (based on conservative assumptions) and 10-40% (based on more realistic assumptions) – but the figure is certainly not less than 10%. In addition, increasing day-time production should result in less evening overtime, thus limiting energy consumption.

2. The Use of Artificial Lighting in the Built Environment

Some workers are forced to spend the majority of their day-time hours indoors, with little or no access to daylight. This unnatural situation has been shown to:

  • Reduce well being
  • Increase accidents
  • Reduce productivityGood lighting design must integrate natural daylight as much as possible into the building and provide a suitable alternative, where this is unachievable. This section will focus on the alternatives to natural daylight.

2.1 Artificial Daylight

One example of artificial daylight is the Virtual Daylight system from Clearvision. The designers have tried to break daylight down into its components and replicate or improve upon them. Clearvision claims that ‘Because several of the characteristics of natural daylight are matched by our lamp and lens combination, the appearance is similar to that from a north-facing window.’

Colour Temperature: The colour temperature of the surface of the sun is 5800K, while average office lighting has lamps with a colour temperature of 3000K. Virtual Daylight offers a range of colour temperatures from 5300K to 7000K, with colour rendering in excess of 80Ra (taking the sun as 100Ra).

Ballasts: to reduce flicker in Virtual Daylight lamps and to offer as steady state light as possible, high frequency ballasts are used (<25Khz).

Polarisation: This technology tries to replicate daylight as opposed to sunlight. Sunlight produces glare, whereas daylight is naturally diffused as it passes through the earth’s atmosphere. With the use of polarised lenses and direct/indirect lighting, Virtual Daylight achieves the same results

Diffusion: Another effect of light travelling through the atmosphere is that it is naturally diffused. This ensures that there is no blinding source of light making it uncomfortable to see.

Colour and Intensity: Natural daylight is never constant. The colour or intensity of the light is affected by the atmosphere. The sky can have a red appearance at times or be perfectly blue on a bright summer day. This has an affect on humans’ biological rhythms, so Virtual Daylight tries to mimic this with a dynamic lighting control system (see 2.2 below).

2.2 Dynamic Lighting Daylight is never constant:

  • The sky may be red in the morning or the evening.
  • Illuminance levels change from approx. 5,000 lux up to 100,000 lux, depending ontime of day, season or weather conditions.Conventional artificial lighting remains constant, with the only change in illuminance levels in a room resulting from infiltrated daylight through the window, skylights etc. Any artificial lighting

system that hopes to mimic daylight, therefore, can not be constant. To demonstrate this, a Philips dynamic lighting system will be referred to – however, lighting manufacturers such as iGuzzini, Zumtobel and Targetti market similar systems.

Dynamic lighting control can change the illuminance level and colour temperature of the light produced. This is achieved by combining the spectral radiation of two different types of fluorescent tube. The control of the system can lie in the hands of the end user or in a pre- programmed cycle.

Fig 2.1 shows a pre-programmed cycle which could be utilised in an office environment. Note that in the morning the users are subjected to 900 lux of cool light and the illuminance level never drops below 500 lux. This ties in with the research on light levels and efficiency outlined in section 1.3.

This type of control system would be more practicable in an open-plan office, where no one occupant has access to the control system. In board rooms or private offices, access to daylight will be greater and the occupant can control the lighting scene themselves, by way of an infra-red control. A very basic view of the system can be seen in Fig 2.2.

As mentioned in section 1.1.2, exposure to very bright light for long periods of time puts unnecessary stress on the body. This system counteracts that by varying illuminance levels, giving the body a more natural environment to interact with.

2.3 Personal Control
Boyce et al, (2005) describe the effect of two experiments on work place productivity.

  • Experiment 1 had four experimental situations: an office lit with direct lighting only; one lit with direct/indirect light with no control; one with direct/indirect luminaires and a switchable desk lamp; and workstation-specific direct/indirect luminaires with control over the direct lighting.
  • Experiment 2 had two conditions: a regular array of recessed prismatic lensed luminaires and one with suspended direct/indirect luminaires.The test subjects found the direct/indirect system more comfortable than the direct system only and comfort was increased further with the individual control in Experiment 1. Participants with desk lamps took shorter breaks and the researchers noted that ‘individual control over lighting has performance benefits’ (Boyce et al, 2005).3. Case Studies

3.1 Educational Buildings
School, universities and other institutions of learning pose an interesting challenge for lighting designers. The occupants of these building have to concentrate for long periods of time and to facilitate this, comfort is a key design point. Heschong et al (2002) demonstrated the relationship between lighting and performance in schools. Comparisons where made with classrooms with and without daylight and concluded that classrooms with daylight facilitated a better learning environment. This is due to:

  • Higher illuminance levels
  • Better colour rendering
  • Improved spectral content of daylight
  • Improved 3D modelling with highlights and shadows
  • Reduction in flicker from electric lighting
  • Improved student and/or teacher morale or performance due to mentalstimulation from varying lighting conditions; the calming effect of contact with the natural world; greater mental alertness due to circadian biomechanical responses to daylight (neuro-transmitter levels) (Juslen, H., no date).About 93% of communication is non-verbal, therefore, it is important that the teacher be adequately lit for students to receive the full educational benefits. If the task (i.e. attending to the teacher) is made more difficult, due to inadequate lighting, concentration levels diminish. To ensure the teacher is appropriately illuminated, vertical illuminance has to be considered and not just illuminance levels on the working plane.As discussed, the lit environment will have an effect on the well-being of the students. Adequate access to daylight is essential for the healthy interaction of the students with their surroundings. In the absence of daylight, lighting control systems such as dynamic lighting or virtual lighting should be considered. Inadequate lighting may lead to headaches and eyestrain (Wilkins et al, 2002) and links have been made in recent years between inadequate lighting and myopia (Wolbarsht, 2002).If the lighting environment is stimulating, the end user’s mental and physiological systems, visual performance, alertness and mood will be improved. ‘Important performance-related benefits of a positive mood include a willingness to help others, better memory, more efficient decision making, increased innovation and creative problem solving ability’. (Isen and Baron, 1991).In summation, adequate lighting design for classrooms should provide:

• • • • • •

3.2
Health care buildings have multiple users and functions — patients, nursing staff, porters, catering staff, visitors etc. Depending on the room, the lighting requirements will vary.

Designing for patients, means designing a comfortable environment in which they can relax and recover. In public wards patients have little control over their environment which may add to patient discomfort. Easy-to-use task lighting can give patients some element of control. In addition, ‘patients who have greater access to daylight have shown improved recovery rates, so the provision of windows, or artificial daylight systems, is advisable’. (LJ, 2006).

However patients are not the sole users of their room or ward. Hospital staff have to be taken into account when designing a lighting system — and the needs of night-time nursing staff present the biggest problem. Hospital staff need to stay alert and vigilant throughout the night, which should require high illuminance levels and a high colour temperatures. However, this would make it impossible for patients to sleep and thus affect recovery times.

Adequate illuminance levels (not just the minimum set out in the lighting guides) Adequate luminance levels on the teacher
A stimulating environment for pupils and teacher
The best use of natural daylight

The use of efficient electronic switchgear
The correctg brightness and colour appearance of light at the right time

Health Care Buildings

One possible solution to provide a separate room with a ‘light shower’. This is similar to the treatment of SAD — the shift worker is exposed to blue-enriched light at a level of at least 750 lux (LJ, 2006). This exposure will suppress the production of melatonin and enhance the secretion of cortisol. The outcome being that the shift workers are more alert and the patients enjoy a healthy sleep/wake cycle.

Yet another user of the hospital room or ward is the patients’ visitors, who provide a cheap and possibly more effective way of monitoring patients and also reduce their stress levels. For these reasons, visitors are encouraged to stay with the patients for longer periods. Like the patients they have little to no control over their environment. As patients need more sleep than visitors, visitor task lighting that does not affect the patients should be installed. A separate area where the visitor can relax should also be provided — for example, a café with warm colour temperature lighting.

Other users of the hospital environment are the medical staff (e.g. doctors). They need adequate lighting to examine their patients and this could be as high as 1000lux. As the patient is in a vertical position, this could cause debilitating glare — a problem that may be overcome by the use of indirect light (Henri, no date) enabling the doctor to examine the patient while maintaining patient comfort.

As technology improves, the hospital environment itself should contribute to the patients’ recovery. Lighting can play its part in this process and should be given serious consideration at the design stage by the client, architect and engineer.

Conclusion
Current lighting designs for artificial environments such as offices, schools and so on are not fully catering to human needs. Lighting design should not be based on fixed illuminance levels, colour temperature or colour rendering alone. Humans do not flourish in a maintained environment – viz. the move away from a.c. in today’s offiices. A modifiable lighting environment that occupants can interact with has been proven to increase general well-being, productivity and creativity. So why artificial lighting isn’t being designed to meet these requirements! One simple answer is that with the drive to energy efficiency, a system that increases illuminance levels, and power consumption, is not going to be popular. Until the focus moves from energy efficiency — or better still, until artificial lighting that emulates daylight is more energy-efficient — this technology won’t be utilised to its full potential and millions of people will suffer the ill effects of unnatural lighting environments.

References

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