LIGHT SCIENCE

Considerations when Considering LED

Compared to HID, fluorescent and other light source technologies, LED fixtures are relatively easy to build. Source some reputable LED chips and an electronic driver, provide proper heat-syncing, and one can produce an operational LED light source as easily as building an electric crane with an erector set.

This ease of LED fixture assembly is extremely enabling. Whereas twenty years ago the lighting industry had been dominated by the ‘big three’ brands (Philips, Osram Sylvania and GE), today there are literally hundreds of LED brands sold into the horticultural, residential and C&I markets. These many brands are produced by varying companies with associated capabilities ranging from reputable/global lighting companies to local garage-shop operations to ‘knock-offs’ sourced from China.

Likewise LED fixtures continue to decline in price and increase in performance, they still require a significant investment, typically having a payback of five years or more. Furthermore, digging deeper into the technology, better-performing, high-quality LED fixtures require a thorough understanding of plant response to light intensity and spectrum coupled with a significant amount of engineering know-how and proper manufacturing practices. Therefore one should consider a number of factors when investing $500 to $1,500 on an LED system.

Light Output

• Fixture Intensity: Assure that the fixture delivers adequate light output for the area being illuminated. See ‘Day Light Interval . . . . Simply Explained’ in the December issue of The Scoop.
• Photosynthetic photon flux (ppf): Confirm that advertised/rated ppf (µmol/s) is measured between 400nm and 700nm. Note that this range is the sweet spot for photosynthetic active radiation (PAR) and does not include UV or IR output.
• Efficiency: Fixture efficiency (light output in µmol per energy consumed in Joules or watts) should be 2.2 µmol/Joule or higher. Expect this bar to continue to rise over the coming years.

Spectral Quality

• Consider white LEDs over blue/red LEDs. While early LED horticultural fixtures focused on red/blue chips, full-spectrum white LED’s are becoming more prevalent due to the more-balanced spectral qualities of white light over monochromatic blue and red.
• In some cases, vary the spectral output of the light source depending on the grow cycle (e.g. veg vs. bloom). Understand the spectral needs of your particular crop.
• Consider the merits of other areas of the spectrum including UV (bug control, favorable plant response) and far red (promoting larger leaf area). LED fixtures can incorporate a percent of chips that deliver wavelengths specific to these spectral regions.

Warranty

• Rated fixture life: Life testing a 50,000-hour fixture to half of its life would involve 3 years of life testing which is not practical and not practiced by manufacturers. Be somewhat skeptical of fixtures with life ratings of 100.000 hours or more.
• Avoid moving parts on fixtures like fans: LEDs operated under their rated thermal limitation should operate for years. On the other hand, the life of fan-cooled fixtures will likely be limited by the life of the fan, not the LED.
• Assure that fixtures are produced by a reputable company. Confirm that the fixture brand provides a satisfactory warranty, covering all components. Make sure that the brand has North American presence.

Other factors to consider

• Is the fixture water tight? Note – fixtures with IP65 ratings can withstand direct water (e.g. from a hose)
• Is the fixture dust resistant? Note – fixtures with IP50 prevent the ingress of dust sufficient to cause harm to the fixture
• How many fixtures do you wish to load per circuit? More fixtures with lower current draw can be connected to a single circuit, thereby reducing related installation costs.
• How easy is the fixture to assemble (if needed) and install?

Visit Sunmaster’s Square Root page for more info on LED grow lights