Lighting Matters: The Scotopic Richness of Artificial Light – Monthly Column featured in EE Publishers’ Vector Magazine

http://www.ee.co.za/article/lighting-matters-the-scotopic-richness-of-artificial-light.html

I feel privileged and excited to have a regular column in Vector. I intend to provide our readers with stimulating, inspirational and interesting content on the science of lighting.

Hopefully, this column will encourage professionals and lighting enthusiasts to learn more about this subject and the equipment and controls which seem to advance at a frenzied pace.

I am concerned over the standard of lighting design in South Africa. I am frequently asked for my opinion or to physically measure illuminance levels at different sites throughout the country. In most cases, lighting designs deliver the average maintained illuminance levels required by outdated regulations, when measured with a standard, seldom-calibrated photometer.

Know that the standard photometer only measures two degrees of the human field of vision. Now, here is the crux: it has no way of measuring the scotopic/mesopic richness of light.

All light sources have a degree of scotopic richness, so a specific light can stimulate the rod photoreceptors in the human eye to work together with the cone photoreceptors. This ability varies from very low stimulation with low-pressure sodium lamps to considerably higher levels with LEDs, depending on the correlated colour temperature of the LED. The only way to measure “LED light” is by means of a spectral irradiance colorimeter.

The aim is to achieve the best and most comfortable light level as perceived by the human eye. It also means that the aim is to illuminate task areas and spaces so that the most comfortable pupil size will result.

This has been known for many years and was propagated by Dr Samuel Berman of the Berkley Institute, but it is not widely-known and is definitely not practised in this country due to lack of understanding and lack of formal teaching of illumination engineering in South Africa.

What are the consequences if we do not pay attention to this phenomenal fact? Well, quite simply, there will continue to be gross over-illumination. This will be even worse where LED is used and workplaces could be over-illuminated by as much as 60 – 80%.

If we over-illuminate, we waste our clients’ money by specifying too much light. This has the knock-on effect of increasing clients’ energy bills, resulting in bad business for all.

I will continue to discuss this subject in the next issue of Vector.


PHILIP HAMMOND

BHA SCHOOL OF LIGHTING – 17 APRIL 2018

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