Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
RESEARCH NOTE: DAYLIGHT AND LIGHTING
Editor’s note:
Significant elements of this research note were originally produced (by the same author) for
the American National Standard Practice for Office Lighting and we are grateful to IES for
allowing that to be reproduced in this format (http://www.ies.org/store/product/americannational-standard-practice-for-office-lighting-ansi-approved-1290.cfm).
We are particularly grateful to Paul Appleby, Guy Newsham, Derek Clements-Croome and
Ashak Nathwani for their efforts in leading the production of this research note.
Introduction
Office lighting must satisfy a variety of human needs. Visibility is paramount to be able to see
the task and its surroundings, but lighting affects many other aspects of wellbeing, including
comfort, social communication, mood, health, safety, and aesthetic judgment.
The key relationships at the heart of this section are those that are dependent upon:
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occupants and their access to windows and a view of the outside;
The balance of daylight and artificial lighting and the consequent implications for
control, energy consumption, solar protection, glare and veiling reflections.
The quality of artificial light where it is required
Numerous studies link access to windows with increased well-being and productivity, although
methodologies vary and it is difficult to separate the benefits of view to outside from the
availability of daylight.
Impact on occupants
Poor visibility, glare, flicker and lack of control of the visual environment can all affect task
performance, whilst visual discomfort may lead to headaches and eyestrain. Good lighting
design requires the selection and layout of appropriate luminaires and their integration and
operation in conjunction with windows and shading.
The amount of light emitted from a source, such as a lamp, is known as luminance, expressed
in candelas per square metre (cd/m2), which is a function of luminous flux (lumens), whilst
the amount of light falling on a surface is called illuminance, measured in lux. The human eye
responds to the light emitted from surfaces leading to a sensation of brightness. If this is
excessive then it is defined as glare, which may be either uncomfortable, or disabling.
Disability glare is a luminous veil cast across the retinal image making it impossible to see, like
looking into oncoming car headlights at night. Veiling reflections are high luminance patches
reflected by specular surfaces such as glossy reading materials and computer screens, and are
a common source of complaint.
Newsham et al (2008a) conducted measurements of VDT screen glare and occupant satisfaction
in 779 workstations in 9 buildings; results showed that the presence of veiling reflections was a
risk factor for dissatisfaction with lighting. Veitch and Newsham (1998) exposed participants to
both lensed and louvered direct luminaires during a full day of simulated office tasks and
questionnaires. The louvered systems were judged as having lower glare, and also yielded
Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
judgments of better self-reported productivity and lower overall task difficulty. In one field
study dating from 1996 77% of occupants reported bothersome glare on computer screens, this
was reduced to 29% with the installation of a glare filter (Hedge et al, 1996). This earlier work
was conducted on CRT screens, whereas LCD screens, which in general have lower reflectivity,
are rapidly becoming the norm. Work with laptop LCD screens of 1999 vintage (Miller et al,
2001), showed acceptability of lighting conditions was inversely proportional to the perceived
brightness of computer screen reflections. Diffuse reflections on LCD screens have been shown
to reduce the average viewing distance between observer and screen, and result in higher
reported visual fatigue (Shieh, 2000).
Some objects are self-luminous, that is, they generate light; lamps and computer screens, for
example. Other objects simply reflect light from other sources, office walls, for example. In
the latter case, the surface luminance is a function of the surface illuminance and the
reflective properties of the surface. For example, a dark grey and a light grey surface can be
lit with the same illuminance yet will have very different luminances. This also exemplifies
why room surface finishes should also be considered as an integral part of the lighting design.
Office occupants generally prefer higher luminance surfaces over lower luminance surfaces,
provided there is no glare. Studies suggest a minimum wall luminance in offices of at least 30
cd/m2. (van Ooyen, 1987; Veitch & Newsham, 2000b).
Some luminance variation among the major surfaces in the field of view may provide interest
and important visual cues. However, variations that are too great will create adaptation
difficulties for the eye and possible dissatisfaction, even if the surfaces when viewed in
isolation would not be problematic. Studies suggest the following upper limits on luminance
ratios for offices:
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Between a paper task and an adjacent Visual Display Terminal (VDT) screen: 3:1
Between a task and immediately adjacent surroundings: 3:1
Between a task and remote (non-adjacent) surfaces: 10:1
In general, variable light patterns create more desirable visual interest than more uniform
distributions, provided the luminance ratio limits and other recommendations above are
respected. For example, seminal studies by Flynn et al from the 1970’s concluded that
relaxation and pleasantness are cued by non-uniformity, particularly non-uniform wall lighting;
spaciousness is cued by uniform lighting and bright walls (Flynn et al, 1973, 1979).
The colour appearance of objects that are not self-luminous depends on the spectral
properties of the illuminating source, and the spectral reflectivity of the object. For example,
a dress which is said to be red reflects light that is predominantly at red wavelengths. When
red light is present to illuminate the dress, as in high-colour-rendering light sources, the dress
appears to be a rich vibrant red. When red light is less present, as in lower-colour-rendering
light sources, the dress does not reflect as much red light and therefore appears muted in
colour and dull in appearance.
Two distinct common metrics are used with respect to colour and light sources: the
chromaticity (correlated colour temperature - CCT) and the colour rendering properties of the
source.
Somewhat counter-intuitively, the higher the chromaticity of the light source the cooler its
appearance, hence a ‘cool white’ lamp will have a CCT of around 4,100 Kelvin (K) whilst a
Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
‘warm white’ source will be between 2,700 and 3,200 K. As the name implies the Colour
Rendering Index (CRI) indicates the colour shift that occurs to a set of reference colours when
exposed to a given light source. Relatively speaking the higher the CRI of a light source the
more vibrant the colour appearance of an object will be.
There is considerable debate in the research community regarding the importance of light
colour on office workers. There is consistent evidence that higher CCT sources, such as natural
light or daylight lamps, with the same CRI and at the same desktop illuminance, will make a
room appear brighter. Similarly, the evidence suggests that for very difficult achromatic tasks
(without colour), higher CCT sources improve performance. Based on this evidence some have
suggested that higher CCT sources at lower illuminances will provide equivalent performance,
and that energy savings can thus be achieved. However, it is important to note that modern
office tasks are generally visually easy, and that task performance effects of higher CCT
sources are not experimentally observed in such conditions. Further in some cultures, such as
North America, higher perceived brightness at higher CCTs is not generally preferred by
observers, who sometimes describe such conditions as “like a hospital”. This highlights the
importance of matching light source spectrum to task and cultural norms.
A common problem with some older high intensity discharge (HID) and fluorescent lighting
installations is flicker, which is associated with increased incidence of headaches and
eyestrain, and reduced task performance. Flicker in such sources occurs only with
electromagnetically-ballasted systems, which cause light from the lamps to fluctuate at twice
the frequency of AC electricity supply, or 100/120 Hz for a 50/60 Hz electrical system. Some
people may detect this oscillation directly; for others who do not perceive the flickering
visually, there is evidence that the neurological system does detect it, which may cause
problems. Flicker may be greatly reduced or eliminated by the use of high-frequency
fluorescent electronic ballasts (which operate at frequencies of 20-60 kHz) and low-frequency
square wave HID electronic ballasts.
Wilkins et al. (1989) changed fluorescent ballasts from magnetic to electronic (and vice versa)
in a real office without informing the occupants. The average incidence of headaches and
eyestrain was more than halved under high-frequency lighting. Veitch and Newsham (1998)
exposed participants to a variety of luminaire types during a full day of simulated office tasks
and questionnaires. Luminaires on some testing days had magnetic ballasts, on other testing
days electronic ballasts were used. Visual performance for low contrast targets was 2.2%
better under electronic ballasts than magnetic ballasts. Performance on reading and writing
tasks, and on a reaction time task, was also improved.
Light emitting diode (LED) or solid state lamps may also exhibit flicker, depending on the
driver technology used. While some LED sources can be almost flicker free, others may have a
‘flicker index’ some five times higher than a typical fluorescent lamp with a magnetic ballast.
High frequency switching power supplies have been developed in an attempt to address this
problem (Grather, 2009). Flicker during dimming is a particular issue, hence it is important to
use a dimmer switch that has been specifically developed for use with LED technology.
Typical recommendations for task illuminances in offices are 300-500 lux, although specific
tasks or populations may require different levels. Newsham et al. (2008b) conducted
measurements of illuminance and occupant satisfaction in 779 workstations in 9 buildings;
results suggested that illuminance in the range 300-500 lux reduced the risk of dissatisfaction
with lighting.
Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
In addition to this experimental evidence, skilled lighting designers report that in their
experience a desktop illuminance of 300 lux is acceptable, if carefully designed. Successful
elements may include a luminaire that delivers light to vertical as well as horizontal surfaces
(e.g. a good direct-indirect luminaire), light-coloured surfaces that keep luminance and
luminance ratio at recommended levels, and a controllable task light.
Nevertheless, studies consistently show that higher light levels are generally preferred, with
diminishing returns at around 1000 lux, provided these higher levels are not accompanied by
glare. Further, studies of the health effects of lighting have concluded that people in
developed countries are generally receiving a light dose too low for optimum health; higher
light doses have been associated with better alertness, mood, and vitality.
A recent study by a Chinese team based at universities in Australia and China illustrates this.
From a laboratory based study using a lighting perception questionnaire they found that level
of light perceived as stimulating by the majority of the 69 undergraduate subjects was 900 lux
or higher compared with a comfort level of between 400 and 500 lux. The stimulating level can
negate fatigue, increase alertness and hence performance. They found that stimulating levels
can have a restorative effect by replenishing cognitive function and this can apply to other
environmental factors too.
However, supplying higher light levels while meeting a desire for lower energy use is
challenging. More use of daylighting is the obvious answer, although solid-state lighting using
some form of light emitting diode (LED) does promise great advances in the efficacy of electric
lighting.
However the evidence is unequivocal; office occupants should have access to windows and
daylight. There are consistent benefits to the occupants in terms of satisfaction and health,
particularly if windows offer views of nature. Daylight (during the main part of the day)
exhibits excellent colour rendering, and may improve object modelling by delivering light from
supplementary directions. Further, appropriate controls over electric lighting allow for electric
lighting to be reduced when daylight is available, thus saving energy (see below).
In the 2008 study by Newsham et al referred to above, the team also conducted measurements
of the physical environment and occupant satisfaction for the 779 workstations visited. Results
suggested that lack of access to a window was the biggest risk factor for dissatisfaction with
lighting. Leather et al. (1998) surveyed 100 workers in a wine producing facility. They were
asked to assess the degree of sunlight penetration in their work area, as well as several
aspects of their job. Higher perceived sunlight penetration was associated with higher job
satisfaction, lower intention to quit, and better well-being. Another study found that those in
proximity to external windows spent 15% more time on productive work than those in internal
offices (Figueiro, 2002). Whilst an analysis of studies reported by the Lighting Research Centre
in 2004 indicates a significant improvement in performance with memory tasks (10-16% better)
for those with a view to outside, but no significant correlation between performance and
daylight levels (Boyce, 2004).
Nevertheless, daylight should be provided within the bounds of the lighting quality criteria
used in the design of artificial lighting. For example, inadequate shading at certain times of
the day or year may cause direct or reflected glare and excessive luminance ratios.
Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
Elevated productivity has also been linked to lighting design, such as the use of ‘workstationspecific direct-indirect luminaires (uplighters with a downward component) with individual
control’ compared with general lighting with no upward component (Galasiu et al, 2007).
Benefits for the employer
Achieving quality lighting involves more than simply specifying the illuminance level to make a
given task visible. Design issues such as glare, shadows, light patterns, light distribution,
flicker, and colour appearance may all affect the office worker’s comfort, social interactions,
aesthetic perceptions, environmental and job satisfaction, and task performance. This should
be of great interest to employers, as these effects can all be linked, directly or indirectly, to
organizational productivity.
Lighting may affect the productivity of organizations via effects on both the cost of inputs and
the value of outputs. Poor visibility may directly affect task performance, and uncomfortable
lighting conditions may lead to headaches and eyestrain, which may elevate absenteeism.
There are also indirect effects, which might be at least as important. Satisfaction with lighting
is one component of overall environmental satisfaction in offices. As demonstrated in field
studies in offices by Veitch et al. (2007), Veitch et al. (2010), and Newsham et al. (2009)
overall environmental satisfaction may be correlated with job satisfaction and organizational
commitment
Reducing energy use for lighting also affects organizational productivity by reducing
operational costs. Of course, if these costs are reduced at the expense of occupant visibility,
health or satisfaction, the overall effect on productivity may be negative. This further
emphasizes the importance of taking a holistic approach to office lighting design.
Control and energy/resource use
Lighting is responsible for 22% of electrical energy use in office buildings. The key principle of
energy-efficient lighting is to provide light only when and where it is needed, in the quantity it
is needed. Clock-based controls may be used to ensure lighting is only on for expected periods
of occupancy. Occupancy sensors may be used to further ensure lighting is only on when and
where people are present during normal periods of occupancy. Daylight harvesting systems
may be used to ensure lighting is only on when and where daylighting cannot provide necessary
lighting. Manual switching or dimming may also be used by occupants to ensure lighting is only
on when and where needed, and may also provide a means of controlling the quantity of light
to the personally preferred level.
The starting point for sustainable lighting is an energy-efficient system. Due to the demands of
energy codes, there is a tendency to select luminaires based solely on fixture efficiency
(overall light output for the number of watts input expressed as lumens/watt). However, it is
worth reinforcing that light source and luminaire selection should be based on providing the
recommended illuminance and quality of light for the office task. In other words, the best
luminaire for a specific condition or function may not be the most energy-efficient. It is better
to take a holistic approach to the overall design to determine how the total allowable project
wattage (which is often limited by energy codes) is achieved by prioritizing the project areas
and tasks.
Controls of various kinds are available to manipulate the output of luminaires in various ways.
Controls may use switching or dimming, and may be manual or automatic. Traditionally, office
lighting has been centrally-controlled, with all luminaires switched on in the morning before
Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
the earliest arrivals, and off in the evening after the last person was expected to leave. Such
schemes can be found in many large, open-plan areas. However, most lighting in small,
distinct areas such as private offices and meeting rooms is manually controlled. Compared to
the traditional, on-all-day schedule, manually switching in individual rooms provides
substantial savings. Although maximum savings may never be guaranteed, most people do use
manual controls in ways that save some energy (Pigg et al, 1996). Therefore, for these room
types, simple manual switching should be the baseline against which automatic switching
performance is compared.
Individuals can have widely different preferences for illumination levels even when doing the
same tasks. Providing individuals with personal control over lighting allows them to select their
own preferred level, which leads to improvements in satisfaction, health, organizational
commitment and energy savings.
Dimming control provides occupants with even finer control of light output, and if occupants
prefer a lower level of illumination, this represents even more energy savings. Further, there
is strong evidence that having such personal control over one’s own workspace lighting confers
benefits for occupant comfort, mood, and satisfaction. The benefits of manual control may
pertain to open-plan office occupants too. However, this only applies if the lighting design
features luminaires that are clearly associated with specific workstations and their occupants.
For example systems have been developed that allow individual control of environment,
including lighting levels, from a computer or screen phone at each workstation or via
smartphones.
Newsham & Veitch (2001) showed that when occupants received a desktop illuminance within
100 lux of their own individual preference they exhibited improved mood, and satisfaction.
Newsham et al. (2004) added comfort to this list of benefits. Boyce et al. (2000) found that
office workers with dimming control had higher ratings of lighting quality and comfort, and
tasks were rated as less difficult. Boyce et al. (2006ab) found personal dimming control was
associated with improved comfort and more sustained motivation.
Energy savings with automated lighting controls, such as daylight harvesting and occupancy
detection, compared to a prevailing fixed system on a timer delivering 500 lux are typically 1025%, when measured in both laboratory (Veitch & Newsham, 2000a; Boyce et al., 2006ab;
Newsham et al., 2008) and during field studies (Maniccia et al., 1999; Jennings et al, 2000;
Galasiu et al., 2007). This latter study demonstrated that when absence detection is combined
with daylight controls (photoelectric sensing) and dimming the saving can be as high as 69%.
Hence energy-efficient lighting and control provide the opportunity to downsize an airconditioning system. By using actual lighting load design values and the expected diversity of
these loads due to automatic controls (occupancy sensors, dimming to compensate for
daylight), the size and cost of an air-conditioning system may be minimized.
Geographical and cultural differences
We have seen that lack of access to windows is the biggest risk factor for dissatisfaction with
the visual environment. Indeed some European countries have laws that require office workers
to have access to windows (Danish Building Regulations) or that lighting be provided by natural
means ‘as far as practicable’ (UK Workplace Regulations).
When electric lighting is on it introduces heat into the space. A building design that admits
daylight and has elevations that are oriented towards the sun also admits solar heat for
Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
significant periods. If natural ventilation cannot be used to prevent temperatures from
reaching unacceptable levels for prolonged periods then mechanical cooling will be required to
remove this heat. If the building is in heating mode, the heat from lighting offsets the heating
provided by the building’s main heating system. Many office buildings experience both heating
and cooling regimes over the course of a year, so the overall effect of lighting on thermal
loads is building and climate dependent.
Newsham et al. (1998) conducted a simulation study for a typical office floor plate in six North
American climates. For each kWh of lighting energy saved, the additional saving in cooling was
about 0.50 kWh in Washington DC, 0.15 in Edmonton, 0.80 in Houston, 0.30 in Montreal, 0.70
in Phoenix, and 0.20 in Seattle. Conversely, the additional requirement for Heating was about
0.25 kWh in Washington DC, 0.40 in Edmonton, 0.10 in Houston, 0.35 in Montreal, 0.00 in
Phoenix, and 0.35 in Seattle. These values are in agreement with a similar study by Rundquist
et al. (1993). The overall effect on cost will depend on the fuels used for cooling and heating
and their pricing, and the efficiencies of the thermal systems.
Seasonal Affective Disorder (SAD) is a depressive illness caused by a biochemical imbalance in
the hypothalamus associated with lack of daylight and sunlight impacting on the human
circadian system. It is generally associated with winter months in the higher latitudes when
days shorten and there is very little exposure to daylight. The symptoms are very similar to
depression and, as with depression, the performance and productivity at work of those
affected can be impacted. A 2011 US study of 771 subjects found a 29.6% drop in productivity
when using a standard test for those reporting symptoms associated with minor depression
(Beck et al, 2011). It has been found that access to broad spectrum lighting that simulates
daylight but without the ultraviolet component is effective in alleviating symptoms associated
with SAD.
Innovations
Demand for electricity over a region is not constant, but follows daily and seasonal cycles.
Typically, to meet peak demand utilities start up peak-capacity generators, or import
additional power from other jurisdictions. A third option is for end users to temporarily reduce
their demand; this is termed “demand response” or “load shedding”. While the initial industry
focus for demand response was on HVAC adjustments, the potential for lighting systems to
contribute is increasingly recognized. In both domains it is important that these temporary
adjustments in building services be designed to minimize discomfort and distraction for
occupants.
For the purposes of demand response to fulfil a utility request to reduce electrical load to
assist in the preservation of grid stability, electric light level may be reduced temporarily from
normally recommended levels. The reduction should be no more than 20%, and should be
achieved by smooth dimming enacted over a period of at least 10 seconds. This reduced light
level may be maintained for no longer than 3 hours. At the conclusion of this demand response
period, the light level must be restored to normally recommended levels.
Amongst a number of studies of occupant reaction to load shedding, Newsham et al. (2009) in
particular demonstrates the importance of a gradual reduction in illuminance. Participants
conducted tasks over a typical workday in an office laboratory with little daylight. Participants
in the morning had a desktop illuminance of 500 lx but after lunch the lights were dimmed by
2% every minute, to a minimum desktop illuminance of 200 lx. Unlike most studies,
participants had no prior expectation of lighting changes. In general, occupants did not detect
this 60% reduction in light level, and there was no overall net effect on task performance.
Health,
Wellbeing and Productivity in Offices
Research Note: Daylight and Lighting
Advances in wireless technology and smart phone application (app) development have been
used to enhance the functionality of general lighting installations. One manufacturer has
developed a system that employs wireless sensors within each luminaire that allow
communication with smart phones via a dedicated ‘app’. This allows occupants to adjust
lighting levels via their smart phones whilst the lighting grid can be used as a pathway for
temperature and humidity controls, whilst also acting as an indoor positioning grid so that
occupants can, for example, find vacant meeting rooms via their smart phone (see Philips,
2014).
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Research Note: Daylight and Lighting
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