Month: December 2018

For photosynthesis, plants use more red  and blue wavelength light than green light within RGB full spectrum.  LED technology enables the delivery of only the wavelengths that are needed most, resulting in reduced electricity operating cost to “feed” the plants and increased ROI of plant harvests.

The next decade offers many opportunities for LED manufacturers, distributors, installers, and the whole host of energy professionals and solution providers. Saving energy and money is the key driver in the adoption of LED lights with high ROI and low Total Cost of Ownership (TCO). Low operating costs and low equipment costs move the needle.  For LED grow lights, the market is about making more of something vs less of something. More plant growth often trumps energy savings!

While LEDs can reduce the operating expense over metal halide and fluorescent grow lights, the real win is when the LED grow lights can shave 10 percent or more off of the grow time to harvest. As an example with lettuce or basil, the average grow time is about 30 days, and LED lights can accelerate the growth to deliver the same harvest weight in 27 days. Over a year, the farmer can deliver 13 harvest cycles vs just 12. One more harvest is meaningful. A 20,000 sq. ft. grow operation (about half an acre and half the size of a football field) can yield over $1.5 million in basil every year. Now, LED lights are about production vs reduction.

Here are some insights about the 21^st century that provide perspective on why the LED Grow Light market is poised for dramatic market growth:

The Challenges:

• Global population has doubled to over 7 billion since the first Earth Day in 1970.
• Humankind may deplete fresh water resources before running out of fossil fuels.
• In America, food travels hundreds and thousands of miles to its destination in many areas.
• America faces increasing health challenges from childhood obesity and an overweight population.
• Low-income households are at the highest risk, given limited access to affordable fresh produce.
• The developing world faces increasing food challenges, given droughts and extreme weather.

The Solutions:

• Leverage the advantages of Light Emitting Diode (LED) technology to provide cost-effective, fresh and organic produce at local levels.

Results:

• Fresh and Cost-Effective Food for the World.

LED Grow Lights = $ Money. The available LED technology and “Smart Controls” enable next generation farmers to grow indoors during the day and at night. They also reduce shipping costs to increase net profit. LEDs will reshape agriculture, because a new generation of urban farmers will use abandoned and un-leased industrial buildings to grow organic food close to the communities that will eat it. This reduces the farm to table distance and cuts the pesticides out of the process.

Not all LED Grow Light are created equal.
If you are in the market to use LED grow lights or seek to expand your sales offerings through a strategic relationship, look for grow lights that meet certain standards. Specifically, look for LED Grow Lights with highest Photosynthetic Active Radiation (PAR) per dollar for vegetation and flowering.

In addition to LED vegetation and flowering fixtures, look for manufacturers that offer custom solutions to meet growers’ needs. Modular design can deliver Photosynthetic Photon Flux Density (PPFD) at varying wavelengths to give growers a competitive advantage.

Look for external driver technology with the ability to program, through smart controls, the cycles to optimize plant growth over multiple growth sessions within a 24 hour period, based on the different types of plants.

Look for fixtures with dimming capabilities to simulate sunrise and sunset and/or to optimize plant growth over multiple growth sessions.

Look for adjustable suspension systems so that the elevation of the light source above the plants is optimized for plant growth.

Look for opportunities to integrate hydroponic and also aquaponics systems into the LED grow operations.  A pound of feed may only yield an ounce of protein from livestock, while a pound of feed for fish will yield closer to a one-to-one pound of protein from a fish, such as tilapia.  Plus, vegetables such as kale are nutrient rich “superfoods” with numerous health benefits: http://advancingyourhealth.org/highlights/2013/09/17/health-benefits-of-kale/

Top Tip on LED Grow Lights:
Choose a commercial LED lighting manufacturer or solutions provider that has the highest Photosynthetic Active Radiation (PAR) per dollar of fixture cost. While higher watts are a negative in building illumination, they are typically a positive with grow lights (all things equal in the wavelengths), because more watts translate into more light for plant growth. The $/watt analysis is also relevant in comparing LED fixtures if the light of the different fixtures is distributed across the grow surface rather than creating hot spots. You can look at the cost per watt as a way to short list LED Grow Lights. Just divide the fixture cost by the wattage and this is a great first line of comparison.

In last month’s blog post, I kicked off a series of about glass in lighting by providing a brief history and mentioned possible ways in which glass could effectively be used to increase lighting performance.  In particular, how it can be modified through glass chemistries (low iron), applied coatings (anti-reflective, conductive, etc.) and surface treatments (acid-etching, patterning, etc.) to optimize optical performance.  In this blog post, I want to continue the series by reviewing and discussing each of these areas in more detail to provide a more comprehensive understanding on how glass can be wisely used to optimize lighting efficiency in lighting applications.

The first major challenge of using glass as a material in lighting is with its inherent material properties.  Glass, as a material, loses 9 to 10 percent of lighting efficiency through reflection and absorption losses as shown in the graphic below.

 

 

Diagram courtesy of Guardian Industries

 

As you can see, 4 percent of light is lost through reflecting off of the first surface, another 2 percent lost through absorption from the FeOx content (0.11 to 0.08 percent) in standard soda lime glass chemistry, and still another 4 percent lost through reflecting off of the second surface.  In today’s world of high-efficiency and high-efficacy luminaire requirements, this is an unacceptable sacrifice and has unfortunately caused glass to be designed out of many lighting fixtures.  However, there are innovative and readily available ways to address this problem with glass and reduce reflection and absorption losses and increase overall light transmission and efficiency. These include using:

• Low Iron Soda Lime Glass;
• Anti-Reflective (AR) Coatings; and
• Surface Treatments and Textures.

The use of low iron soda lime glass attacks the 1 to 2 percent absorption losses mentioned above by reducing the FeOx content of the glass chemistry down to 0.2 to 0.3 percent and all but eliminates absorption losses.  The spectral graph below compares the transmission curves at NADIR (0 degree incident angle) of standard soda lime glass and low iron glass with special attention given to the visible range where luminaires perform in:

 

 

Diagram courtesy of Guardian Industries

 

You can clearly see a boost of 1 to 2 percent of light transmission gained just from the replacement of the substrate material itself with low iron glass.  However, that still leaves 8 percent of lost light transmission due to reflectance losses to recover to gain optimum luminaire efficiency.  How can that be undone?

Anti-Reflective (AR) coatings can be effectively used to reduce reflection losses and increase light transmission in lighting as well as many other commercial applications.  In fact, they are already commonly used in eyeglasses, picture frames, and photovoltaics.  The principle of AR coatings is to minimize the interference of light traveling through a given material’s surface versus that of its immediate surrounding environment (in this case, air).  Therefore, the goal of an AR coating with a glass lens in lighting is to create this interference layer with a refractive index (n) as close as possible to air (n = 1) and the glass surface (n = 1.52) to filter the reflection losses and bridge that optical gap.

Adding a 3-layer AR coating (medium, high, and low index gradient) to a low iron substrate, mentioned above, allows most of the 8 percent reflection losses to be recovered in light transmission and efficiency.  The spectral graph below compares the transmission curves at NADIR (0 degree incident angle) of standard soda lime glass and low iron glass as well as application of an AR coating on one (singled sided or SS AR) and both (double sided or DS AR) sides of the low iron glass (again with special attention given to the visible range where luminaires perform in):

 

Diagram courtesy of Guardian Industries

 

A reduction of reflection losses from 4 percent down to 0.5 percent per surface can clearly be seen and allows a Low Iron substrate with Double-Sided Anti-Reflective coatings to reach 99 percent light transmission (efficiency) in the visible range.  The absorption and refection losses seen earlier with using standard soda lime glass have been all but removed at the 0 degree incident angle.

But what about angular losses in light transmission? Since most LED-based luminaires are dispersing light in very aggressive light distribution patterns there is limited value in maximizing light transmission at a 0 degree incident angle only.

The combination of Low Iron glass and AR coatings also help with the reduction of angular losses as shown in the material output files from LTI Optics of standard soda lime glass, low iron glass, and Single-Sided and Double-Sided AR coatings on low iron glass:

 

Diagram courtesy of Guardian Industries

Where:  τ = Transmission, α = Absorption, and ρ = Reflection

As these plots show, the average light transmission achieved with standard soda lime glass from 0 to 75 degree incident angles is only 86 percent whereas low iron reaches 88 percent, SS AR on low iron 90 percent, and DS AR 94 percent and holds > 90 percent light transmission up to 55 degrees (when standard glass only reaches that at 0 degrees).  Clearly, the combination of low iron glass and AR coatings help reduce angular light losses as well.

Finally, another method of reducing reflection losses with glass is by modifying its surface texture.  There are two commercially ready methods of doing this:

• Acid-etching the surface to make the glass “frosted” or “diffuse”; and
• Texturing (or patterning) the surface while the glass is still in its molten form.

Comparing standard clear glass (as a reference) to various acid-etched and textured products combinations (with and without an AR coating), you can clearly see benefits of modifying the glass surface to increase your light capture over angle with all cases providing superior performance versus standard soda lime glass:

 

Chart courtesy of Guardian Industries

In summary, glass indeed has some inherent challenges for effective use in the high-performance and energy-efficient LED luminaires of today.  However, with the use of innovative glass chemistries (low iron), coatings (AR), and surface modifications (acid-etch, texturing) these challenges can not only be removed but also allow for even higher levels of efficiency and efficacy to be achieved.

In my next post, I will provide some case study examples of effectively using these innovative uses of glass lenses, which provide both performance and economic (ROI, TCO, etc.) benefits in selected applications.