General lighting v task lighting
For many years the conventional method of interior lighting for workplaces was by ‘general illumination’. As lighting was not expensive to purchase, install or operate, the principle was to provide illumination over the whole floor area with a high degree of uniformity. This enabled plants or furniture to be positioned anywhere in the space and easily moved without recourse to changing the lighting array.
[Council House 2 - Offices. Spot the five sources of light....]
However, for the past decade UK lighting codes and standards have recommended not ‘general’ but ‘task’ lighting. The significance of this change has either been ignored or gone largely un-noticed as the illumination values were basically the same. The new concept recognised that the main critical visual task is only carried out over a small part of the total floor area.
The rest of the space is used for circulation, storage, filing and similar activities all of which are less demanding in terms of illumination. Lighting the whole area to the highest illumination required can use about a third more energy than matching the illumination to the different activities.
Energy costs are continuing to rise and therefore providing the right amount of light only where it is needed is beneficial both economically and environmentally. Also, variation in illumination can make the space visually more interesting than overall uniformity.
Normally the reason for still providing ‘general’ illumination is because the building is a speculative development and there is no client to determine the furniture layout, or simply that the layout has not been decided yet. Potential tenants need to be aware that for lighting to be visually efficient the equipment should be electrically efficient and the lighting design should suit the activities across the space. Providing light where and when it is not needed is inefficient regardless of lumens per watt performance of the luminaires.
Recommended illumination levels in the past were based upon the need to determine detail in the visual task, together with the amount of contrast critical work and the importance of colour discrimination. Recently there have been massive changes to how we read the written word with print on paper largely being replaced by self-illuminated screens of computers, tablets, telephones, information signs, cash registers, etc. At the same time there has been the move towards ‘hot desking’. No longer does a space have a constant lighting need. The visual task performed at any point will depend upon the occupant at any one time.
Does this mean we should revert to general illumination? Or does the lighting of our buildings require a fundamental rethink so it is more appropriate to today’s sometimes conflicting needs of energy conservation, use of electronic media devices and flexible occupancy of spaces?
Modern lamps have long lives and therefore lighting is only infrequently changed. Installations over twenty years old are not uncommon, a time span when most other electrical equipment will have been replaced several times.
[NB: 'Accent lighting' is the ‘...highlighting of displayed merchandise or the features of a store or building.’ Ref. BRE’s The essential guide to retail lighting.]
This article originally appeared as a --BSRIA blog, Taking lighting to task, published in September 2011 and written by Richard Forster.
--BSRIA
[edit] Related articles on Designing Buildings Wiki
- Artificial lighting.
- Colour Rendering Index CRI.
- Commercial lighting.
- Daylight benefits in healthcare buildings.
- Daylight factor.
- Daylight lighting systems.
- Daylit space.
- Emergency lighting.
- Light pollution.
- Lighting.
- Lighting and offices.
- Lighting control
- Lighting of construction sites.
- People-friendly lighting controls.
- Rights to light.
- Types of lighting.
- Wellbeing.
Featured articles and news
Retrofit 25 – What's Stopping Us?
Exhibition Opens at The Building Centre.
Types of work to existing buildings
A simple circular economy wiki breakdown with further links.
A threat to the creativity that makes London special.
How can digital twins boost profitability within construction?
The smart construction dashboard, as-built data and site changes forming an accurate digital twin.
Unlocking surplus public defence land and more to speed up the delivery of housing.
The Planning and Infrastructure Bill
An outline of the bill with a mix of reactions on potential impacts from IHBC, CIEEM, CIC, ACE and EIC.
Farnborough College Unveils its Half-house for Sustainable Construction Training.
Spring Statement 2025 with reactions from industry
Confirming previously announced funding, and welfare changes amid adjusted growth forecast.
Scottish Government responds to Grenfell report
As fund for unsafe cladding assessments is launched.
CLC and BSR process map for HRB approvals
One of the initial outputs of their weekly BSR meetings.
Architects Academy at an insulation manufacturing facility
Programme of technical engagement for aspiring designers.
Building Safety Levy technical consultation response
Details of the planned levy now due in 2026.
Great British Energy install solar on school and NHS sites
200 schools and 200 NHS sites to get solar systems, as first project of the newly formed government initiative.
600 million for 60,000 more skilled construction workers
Announced by Treasury ahead of the Spring Statement.
The restoration of the novelist’s birthplace in Eastwood.
Life Critical Fire Safety External Wall System LCFS EWS
Breaking down what is meant by this now often used term.
PAC report on the Remediation of Dangerous Cladding
Recommendations on workforce, transparency, support, insurance, funding, fraud and mismanagement.
New towns, expanded settlements and housing delivery
Modular inquiry asks if new towns and expanded settlements are an effective means of delivering housing.