Defining Photosynthetic Photon Efficacy
There has been some discussion online and in presentations recently about the issue of photosynthetic photon flux. The argument goes as follows: Photosynthetically Active Radiation (PAR) is somewhat arbitrarily defined as optical radiation within the spectral range of...
Designing an Ultraviolet-C Disinfection System
Published 2020/05/29 by the Illuminating Engineering Society as https://www.ies.org/fires/designing-a-uv-c-germicidal-system/. Germicidal lamps emitting ultraviolet-C (UV-C) radiation have been in use since the 1930s (Wells and Wells 1936). These are most commonly...
Climate-based Annual Daylight Modelling for Greenhouses with Supplemental Electric Lighting
This is a preprint of a paper presented by the author at the International Society for Horticultural Lighting (ISHS)'s GreenSys 2019 conference in Angers, France in June 2019, and scheduled for publication in Acta Horticulturae . Abstract Recent advances in LED-based...
Greenhouses and Light Pollution
Supplemental electric lighting for greenhouses may be essential for extending the growing season in northern climates, but it comes with a not-so-hidden cost: environmental light pollution. The consequences of this pollution may range from irate neighbours in rural...
Ultraviolet Disinfection for Consumers
In these unfortunate times, it seems that everyone is looking for ways to help with the COVID-19 crisis. From a lighting designer’s perspective, one solution is obvious: ultraviolet radiation. We have known about the disinfectant properties of ultraviolet radiation...
Circadian Lighting – An Engineer’s Perspective
Ian Ashdown, P. Eng, FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 19/11/14. Whether you call it “circadian lighting,” “biologically effective lighting” or some other name, the principle is the same: the color and intensity of light can be used to...
Light Transmittance through Greenhouse Glazing
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 18/10/01. Look at a greenhouse manufacturer’s product specifications and you will see that the light transmittance of single-pane clear glass is typically 88 to 91 percent. Compared...
Far-Red Lighting and the Phytochromes
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published 18/06/04. Most LED grow lights feature blue and red LEDs whose peak wavelengths – approximately 450 nm for blue and 660 nm for red – have been chosen to coincide with the spectral...
The Science of Near-Infrared Lighting
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 18/07/13 There is a common-sense argument being presented in the popular media that since humans evolved under sunlight, our bodies must surely make use of all the solar energy...
Melanopic Green
Ian Ashdown, P. Eng. FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 18/09/03 Numerous medical studies have shown that exposure to blue light at night suppresses the production of melatonin by the pineal gland in our brains and so disrupts our...
Solid Angles
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2014/07/26 Do you suffer from math anxiety? A surprising number of us do (e.g., Wigfield 1988). I would tell you the exact numbers, but you would need to understand...
Understanding Mesopic Photometry
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2013/10/08 If you are involved with outdoor area or roadway lighting design, you will undoubtedly encounter such terms as mesopic multipliers, scotopic lumens, and S/P ratios,...
Thoughts on Color Rendering
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2014/01/05 UPDATE 14/10/06 - LightingEurope, the "Voice of the Lighting Industry," has just published their LightingEurope Position Paper on Color Quality. To summarize:...
The Kruithof Curve
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2015/01/12 UPDATE 16/04/09 - This metastudy: Fotois, S. 2106. "A Revised Kruithof Graph Based on Empirical Data," Leukos. (Published online 08 April 2016, DOI...
Sports Lighting Regulations
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2016/04/30 This blog article has a somewhat frustrating history. About a year ago, I was asked to volunteer my time to write a primer of light and color as it...
Solar Illumination
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2015/01/21 Lighting design is based in part on the reasonable assumption that photometric units have precise definitions. The candela, for example, has a precise...
Seeing Ultraviolet
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2015/10/26 UPDATE 15/11/08 - The following text briefly notes that some people can see near-ultraviolet radiation following cataract surgery due to the UV transmittance of...
Rethinking the Photometric Data File Format
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2017/03/01 If you perform lighting design calculations today, you can thank the efforts of the IES Computer Committee (IESCC) some thirty years ago. Its members recognized an...
Phytochrome and PSS
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2016/12/09 Horticultural lighting is currently one of the fastest-expanding markets in commercial lighting, with projected revenues of several billion dollars in less than a...
Photometry and Photosynthesis
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2014/12/10 UPDATE 15/04/13 -- This article was first published on December 10, 2014. A revised version was published as "LED Lighting for Horticulture" in the Mar/Apr 2015...
Mobile Light Pollution
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2016/01/21 At first glance, this appears to be an innocuous question: How much light pollution is attributable to automotive headlights? It is also a good question in that if...
Mesopic Photometry and Statistics
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2014/04/21 One of the joys of statistics is that you can never be proven wrong ... In a previous All Things Lighting article titled "Understanding Mesopic Photometry" (October...
Light Pollution and Uplight Ratings
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2015/07/20 "Oh, East is East, and West is West, and never the twain shall meet." When Rudyard Kipling wrote this line in his poem The Ballad of East and West (Kipling 1892),...
LICASO and DAYSIM
Ian Ashdown1, Chris Jackson2, Joel Spahn3, Todd Saemisch3 1. SunTracker Technologies Ltd., Victoria, Canada. 2. Lighting Analysts Ltd., London, UK. 3. Lighting Analysts Inc., Littleton, CO. Published: 2017/02/11 LICASO and DAYSIM are daylighting analysis...
Kruithof Revisited
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2015/11/24 A previous blog article -- The Kruithof Curve -- examined the history of the Kruithof curve (Kruithof 1941]) shown in FIG. 1: FIG. 1 – Kruithof curve, modern version...
In the Blood
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2014/06/25 We most often think of lighting design in terms of lumens, color temperature, and CRI, but there are occasional situations where a deeper analysis is required. One...
In Search of Luminance
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2014/11/18 The IES Lighting Handbook, Tenth Edition (IES 2010), describes luminance as "perhaps the most important quantity in lighting design and illuminating engineering." This is...
Horticultural Lighting Metrics
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 08/04/2017 UPDATE 17/08/26 - This article was first published on August 25th, 2017 in Urban Ag News. It was all so easy until recently. Plants require light in...
Giving Light
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2014/05/12 Giving light ... this phrase symbolizes a new philosophy of lighting design, a philosophy in the sense of how we think about the lighting design process. Much like the...
Filtered LEDs and Light Pollution
Ian Ashdown, P. Eng., FIES, Senior Scientist, SunTracker Technologies Ltd. Published: 2016/03/03 UPDATE 2016/03/03 - Revised Figure 6. The problem is astronomical -- the blue light emitted by LED roadway luminaires has been shown to contribute to light...