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Defining Photosynthetic Photon Efficacy

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...

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Greenhouses and Light Pollution

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...

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Ultraviolet Disinfection for Consumers

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...

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Far-Red Lighting and the Phytochromes

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...

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The Science of Near-Infrared Lighting

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...

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Melanopic Green

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...

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Solid Angles

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...

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Understanding Mesopic Photometry

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,...

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Thoughts on Color Rendering

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:...

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The Kruithof Curve

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...

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Sports Lighting Regulations

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...

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Solar Illumination

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...

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Seeing Ultraviolet

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...

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Rethinking the Photometric Data File Format

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...

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Phytochrome and PSS

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...

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Photometry and Photosynthesis

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...

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Mobile Light Pollution

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...

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Mesopic Photometry and Statistics

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...

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Light Pollution and Uplight Ratings

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),...

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LICASO and DAYSIM

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...

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Kruithof Revisited

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...

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In the Blood

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...

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In Search of Luminance

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...

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Horticultural Lighting Metrics

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...

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Giving Light

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...

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Filtered LEDs and Light Pollution

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...

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