Shedding Light: Proper light at the proper time – monthly column featured in Sparks Electrical News (Crown Publications)

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Every morning, I receive the daily release of a science journal. This morning I was absolutely fascinated to read that climate change is making the Earth dimmer. Yes, earth is reflecting less light, here it is natural light being discussed and not artificial light which is also the subject of another topic – Light Pollution. I do not want to delve into this subject now, but I encourage readers to do their own research to find documents relating to this subject.

Now, on with the final episode in this fascinating world of light and lighting design.

On 3rd October 2019, The International Commission on Illumination (CIE) issued a Position Statement on the Non-Visual Effects of Light which recommended the proper light at the proper time. It embraced CIE S 026:2018: CIE System for Metrology of Optical Radiation for ipRGC-influenced Responses to Light.

You may be wondering what ipRGCs (intrinsically photosensitive Retinal Ganglion Cells) are. Well, they are a set of receptors situated in the retina in our eyes together with the rod and cone photo- receptors which are solely for vision. The ipRGCs respond to light and are responsible for the control of our Circadian Rhythms in other words our internal body clocks. The production and release of different hormones and the functioning of our organs as well as the production and release of melatonin by the pineal gland at night, are all down to the ipRGCs.

It is for this reason that we refer to Human Centric Lighting which is exactly what the CIE have explained in their Position Paper. When we wake in the morning, we need more light and stimulation to become alert and tackle our daily tasks, as we become attuned to the day, the intensity and colour of the light can be retuned to lower intensity and less short wavelength radiation of light. Finally, as we prepare to end the working day and return home, the intensity is further reduced and a warmer colour light is introduced so that when we arrive home, we are ready to rest, relax, have dinner, and retire for the night to get a good eight hours of sleep before the start of the next day. We effectively recharge our internal ‘batteries’.

How do we know if our eyes are getting the correct stimulus? What is the desired level of Circadian Stimulus? Well, according to the CIE, leading neurologists, scientists and ophthalmologists, the correct Circadian Stimulus (CS) is 0.3 during the day whilst at work and 0.1 when at home relaxing.

The important measurement in order to be able to calculate the CS, is Circadian Light (CLA). Circadian Light is the measurement of light that enters the human eye when seated at a workstation/desk. So … how do we calculate that? This is where a high level of proficiency is required in the use of Relux Desktop. You have to know and understand how the various calculations are executed within Relux Desktop. You also need to understand how to navigate through the Calculation Manager. The degree of accuracy and the different measurements that you want to produce will depend on this. It is also important to understand that the automatic raster setting in the Relux Desktop calculator will produce results which can be used as accurate light measurement points when verifying the results post installation according to the lighting design using a photometer. You will not need to compile your own measurement grid.

Next, it is important to preferably use the Maintenance factor for each luminaire rather than the classical method where you would simply select 0.9 for LED in accordance with SANS 10114-1:2020.

When using the Maintenance Factor for each luminaire, you are able to select the environment, the correct surface and material reflectances, the maintenance interval i.e., cleaning, etc, whether the luminaire is direct or indirect or direct/indirect, and finally, you can set to calculate manually or automatically. We prefer not to use the Tick Box for manual but rather to enter the L factor which for LED is usually 80, the lifetime of the LED being used i.e., the number of hours and lastly the estimated operating time of the LEDs for the application. Relux Desktop will the calculate the Maintenance Factor for the specific LED Luminaire.

Now it is time to set Expert Mode in the Calculation Manager. Enter the EVE from the tables in IES TM-24-13 in the field luminous flux factor. Now select Reason and type in “EVE factor applied according to IES TM-24-13”. This will now report in the lighting design report when you have completed your lighting design.

For CLA measurement and CS calculation, it is now time to insert observer TI making sure that once inserted, adjust the angle of inclination, viewing direction, observer age and the distance set to 1.2 m which is the average human face height when seated at the desk. Make sure that the cut-off angle is set to zero. Here we are using the measuring object that we would normally use in street lighting designs for Threshold Increment to calculate the vertical measurement of the observers at their desks.

Once again, modern lighting design for LED lighting and taking the well-being of the occupants into account to be compliant with all standards, regulations, CIE directives and WELL Building standards for occupant well-being credits.

For more detail on the subjects covered in this series, about Relux Desktop advanced use and about lighting courses with internationally recognised qualifications, readers are welcome to contact me directly.

Until next month, stay safe!

BHA SCHOOL OF LIGHTING – 23 November 2021

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Copyright © 2021 BHA School of Lighting, All rights reserved.

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