How much light do we need?

Olympic ring sunglasses with flashing LED lights

Olympic ring sunglasses with flashing LED lights

As electric lighting developed, recommended light levels were raised. This was due to; in part, increased luminous efficacy of lamps, overall national prosperity and the availability of relatively cheap electricity. However, with the oil crisis in the 1970s energy costs suddenly rose steeply and lighting levels became static and are basically the same today.

More recently, many common visual tasks have been made easier by the introduction of electronic visual displays replacing printing and handwriting and many office occupants are satisfied with lighting levels less than the recommended 500 lux.

In future should lighting levels be based, not simply on visual efficiency, but on requirements of good health? Electric lighting originally supplemented daylight but now we are totally dependent upon it and people are rarely reliant on daylight alone whilst indoors. Deep plan offices and shopping malls are illuminated all the time regardless of the amount of daylight available. Traditional outdoor sports are now played in enclosed stadia and at night. Even our cars have tinted windows to reduce the amount of daylight. Lifestyles today spend less time outdoors. A lunchtime kick-about outdoors in the car park is more likely to be a sandwich at your desk these days.

Seasonal affective disorder (SAD) was identified in the 1980s and is considered to be because of the lesser amount of daylight during the winter months (for northern hemisphere). Treatments suggested include exposure to 10,000 lux of white light for at least one hour a day, although more recently 300 lux of green light is considered to be equally effective.

I can remember my grandfather suggesting that time should be found to view the distant green hills, and he offered two reasons. To focus at ‘infinity’ relaxed the eye muscles, and green was a restful colour in the middle of the visual spectrum. He was a countryman at heart and I suspect it also gave him a chance to dream.

Introducing more daylight in our lives must be a benefit. We just don’t know how to quantify its value.

Book Review: Death of a lightbulb, John Otten (2012)

Otten, John. (2012) Death of a light bulb. Blue Ocean Publishing. (ISBN 978-1-907527-08-1)

This book examines electric light, not simply as a technological invention but as the creation of a worldwide industry which has transformed the quality of life for millions of people. The humble domestic light bulb has long been an icon for inventiveness and inspiration. It well deserved this recognition when its impact on civilization in the last century is considered. Much has been written about the early struggles to find suitable materials for filaments and machinery capable of creating a high quality vacuum. Electric light was highly desirable and a great improvement over the flickering and odorous alternatives. It directly led to public electricity generation and distribution. It is difficult for those living in the Western World today to imagine life without electricity.

To meet the demand required investment and speculation on an amazing scale together with mass production of the lamps. It is this story about creating industrial empires and the lengths then taken to protect their profits and assets. Competition and co-operation existed side by side with all the weapons of modern business. These included controlling ownership by shareholders, webs of intermediary companies, and legal contests. The application of patents provided protection and the opportunity to control market penetration. Global transport and distribution had not been fully developed so to reach distant markets could mean agreements with companies considered as direct competito rs nearer to home. Cartels could influence supply and retail pricing. Many of these actions would be considered dubious today with calls for greater transparency and level playing fields.

This story has not been documented for many years and John Otten has provided an insight into the complex web of a modern, highly successful industry. His extensive research into areas not always well documented is to be commended and is augmented by his long career within the lamp making industry. Previous work was written around the first half of twentieth century and information regarding the second half of twentieth century makes a valuable addition to lighting history.

The title makes reference to the final twist in the story. Most products follow a conventional life cycle with sales rising to a peak and slowly going into decline. With many modern devices this life cycle can be a very short period of just a few years, but the light bulb appeared to be almost everlasting. It did not fade away but has been virtually executed by European legislation banning its production and sale. This policy has also been accepted by other countries around the world but is not yet universal with the United States, New Zealand and Canada still fighting in some quarters for its survival. This final phase is still being acted out and the full story behind it may not appear for some time but in the meanwhile the life of the lamp making industry is a worthy model to study of how to turn a simple idea into a life changing experience for millions of people.

Are designers keeping up?

BS EN 12464-1, Light and Lighting, Part 1 indoor workplaces, was first published in 2002. It included a schedule of recommended minimum task illuminances for a range of industrial, institutional and commercial applications. These values were similar to those previously in the Society of Light and Lighting Code. Originally the SLL values were ‘general’ illumination for the complete floor area thus enabling equipment and workers to be positioned anywhere in the space. A convenience when electricity was cheap.

However the BS specifically refers to ‘task’ illumination, normally only a small part of the gross floor area. The rest of the room would require less illuminance and thus considerable capital and operating cost savings can be made. But where are the task areas? Often the client has no idea when the lighting design is carried out. The designer then has to revert to ‘general‘ illumination to guarantee adequate lighting of the task. However the client will pay for the over lighting of the ‘non-task’ areas.

This problem of insufficient information is compounded by the changes included in the revision to BS EN 12464-1 last year. Introduced for the first time is the requirement for mean cylindrical illuminance in the space to provide good visual communication and recognition of objects. This should be no less than 50 lux, and for areas where good visual communication is important like offices, meeting and teaching areas not less than 150 lux. Although the concept of cylindrical illumination is not new it has not been widely considered for the routine lighting of workplaces.

How do many existing lighting schemes meet these new requirements? Very few published photographs of interiors include a full complement of ‘workers’ so there is little subjective evidence of how modern lighting affects the appearance of the human face. Accurate measurement could be a problem. Added to this is the same problem outlined above, the lack of occupational information of the space.

The Standard only considers the requirements of ‘workers’ so places where customers or visitors dominate lighting requirement need to be considered separately.

Are Compact Fluorescent Lamps welcome in your home?

Fluorescent lamp technology is certainly not new and when linear lamps became available after the Second World War their advantages were rapidly recognised by both industry and commerce so that by the 1970s fluorescent lighting had become a standard method of interior lighting for most buildings.

It therefore seemed reasonable that Compact Fluorescent Lamps (CFLs) introduced in the 1980s would be equally well accepted in the home by domestic consumers. However home users were not immediately impressed by the long-term savings, and were deterred by the high initial costs. Indifferent or poor colour rendering, physical incompatibility, mercury hazards, unfulfilled marketing claims and slow warm up were perceived as disadvantages.

 The arguments for and against CFLs became polarised and European governments decided to tip the scales by “banning” domestic filament lamps. Retailers meanwhile adopted “loss leader” pricing of CFLs and the popular national press reacted with health scares from mercury and ultraviolet radiation. The consequence was consumer confusion. However the argument has shifted with rising energy costs having a significant impact on domestic budgets and technological progress has addressed to some extent the earlier quality issues.

 There is now the opportunity to make a more rational judgement. Most information has been biased one way or the other. However there is now an independent and thorough assessment of CFLs that factually examines many of the issues and is well worth reading:

“An examination into the use of CFLs in the domestic environment”. James Thomas Duff (2011) has been published in the new CIBSE SDAR Journal for September. 

 No single lamp type can solve all lighting problems. The choice should be determined by the particular activities and thus the lighting needs of the occupants, rather than the architecture or design of the dwelling. Many building services operate in part to preserve the fabric and environment whereas lighting is only required when the space is occupied. As soon as it is vacated the lighting can, and should be switched off. Lighting is for the people, and the home is where personal character prevails. The choice is yours but hopefully it can now be based on sound facts rather than scare-mongering or “prohibition”.

Taking lighting to task

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 subsequently 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. I think 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 nature of the 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. 

Wasted light

Part of the efforts to improve the energy efficiency of buildings is to set air tightness requirements. At the same time natural ventilation is being considered as a viable option to mechanical air conditioning.

There is a parallel with lighting where the use of daylight has benefits for both energy consumption and occupant well-being. The past age of cheap electricity however encouraged architecture to ignore daylight and to assume electric lighting to be available at all times. This magnanimous use of light continues today, demonstrated by the national press regularly showing large office blocks with all their lights blazing long after the workers have gone home.

This presents two opportunities to save energy. The first is to optimise the use of lighting controls coupled with the education of building users and occupants. If people do not understand the need to switch off when vacating a space then it is likely that any lighting controls installed will change this behaviour.

The second aspect is the amount of now expensively produced electric light that simply goes out the window. After dark this loss could be reduced by blinds provided they are drawn. Perhaps there is a photochromic sensitive glass that becomes opaque and highly reflecting when there is an absence of daylight.

So how about a campaign for “light-tight” buildings? Something to consider for the 2013 edition of Part L?

Richard Forster is a Lighting Expert with over 40 years experience in lighting, both as an engineer and consultant. As a well-respected author and lecturer, his wealth of knowledge is continually used by BSRIA.

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