I realise as I write this article for the July edition of Sparks Electrical News, that we have passed the halfway mark for the year and from here on it is downhill all the way until the end of 2022.
The next chapter in our series of light is about ‘Standards and Compliance’. It is essential to have a detailed knowledge about this topic, so much so that Joseph Rey-Barreau, a New York lighting designer and architect said: “It’s a new world of lighting. People must think about it more than ever.” Albert Hanley, another architect, said: “Design is defined by light and shade and appropriate lighting is enormously important.”
Introduction
We learned that the eye responds to the stimulation of light. The light is converted on the retina into electric signals which are transmitted to the brain where the picture is formed. The object or scene is seen in shades of grey when the illumination level is low, but as the illumination level increases, we are able to distinguish colours and enjoy better acuity. This is typical for an observer with normal, or near normal, sight. People who have alternative colour vision will see the object or scene differently. This is not covered in this course but in later courses as it is a specialist topic.
The object or scene is seen subjectively by the observer because of the eye’s ability to adapt to different illumination levels. This subjectivity of illumination levels must be converted into an objective assessment so standards can be applied and standard meters can be used to measure the light levels. The illumination level suitable for one person to work efficiently, may not be suitable for another, for example, the age of the observers may be different.
Research has been carried out over many years to recommend the illumination level that would most likely please most people who perform a particular task. In these studies, the tasks were made independent of the literacy of the worker and one such study was the use of the ‘Landolts Ring’ which is a ring with a small break in its circumference similar to a ‘C’. The rings were grouped in arrays of 5 by 5, with the opening in the rings pointing in different directions. Some of the rings had their openings pointing to twelve o’clock and the observers were asked to count or mark these within a specified time. The sheets of rings were changed and so the illumination level changed, and the exercise was repeated. The new sheet of rings may have larger or smaller rings or the contrast of the ring to the background was reduced. These changes made the task easier or more difficult for the observer and the performance of each test was recorded. The sheets can be related to various work tasks and this formed one of the bases for the standard illumination levels in codes of practice in many countries. The illumination level recommended satisfied 90% of the users with a 90% performance level.
A number of tests were carried out in this way and many field measurements were taken to establish what the illumination levels should be for the task. The accuracy, safety and the comfort of the performer was considered. These recommended illumination levels have been included in the design guides and codes of practice in many of the participating countries, including South Africa. In 1996, the SABS Code of Practice 10114: The lighting of interiors Part 1 Artificial Lighting was published. The code recommends illumination levels for safety and for productivity.
The SANS (South African National Standards)
SANS recommend illumination levels for productivity at a 90% level of performance for the average worker within an age group up to 25-years of age. The recommended illumination levels listed are for most of the tasks encountered in industry, the hospitality industry, schools and homes. The code describes how the field measurements must be made. In many installations, the task that will be performed in that area may not be known and the tasks were assumed so that the lighting design could be done. The selected illumination level is then provided across the complete area. Later, when the building is occupied, the task actually performed may be different, or many only performed in a small part of the area. In this situation the lighting design should be modified to suit the new layout, so that the lighting design complies with the recommended code of practice.
The standards define how the illumination levels may change near and within the field of vision. This recommendation is for the comfort of the worker and for his or her safety. The code recommends that the illumination levels should be within the ratio of three to one close to the task. The worker’s eye will then be used to working at one illumination level and will not have to adapt to different levels, which will cause eye fatigue. The eye muscles will get tired if they constantly have to change the iris position, due to the light levels and focusing on the detailed task. The recommended variation of the illumination levels within 5 m of the task must be within five to one, so the eye does not have to adapt to new light levels, which may cause temporary blindness and could cause an accident. This is similar to the blindness experienced when one walks into a dark room after being in full sunlight. The eye has to adapt to the lower illumination level. Another example is the blindness experienced after a flash from a camera.
SANS 10114-1:2020: Lighting for Interiors updated in 2020 for the first time in a long time is based on the European Standard EN 12464-1: 2021: Lighting for Interiors. Unfortunately, SANS 10114-1: 2020 is a poor copy of the European Standard EN 12464-1:2021.
I therefore encourage all lighting designers and consulting electrical engineers to purchase their own copy of EN 12464-1: 2021 and to use the highest available international standard. We must not accept mediocrity.
Once again, I am always prepared to assist any readers and give basic advice about lighting to minimise their risk of non-compliance. Next month we will take a closer look at some more standards that are applicable to lighting and lighting design.
Enquiries: phil@bhalighting.co.za
