Daily Light Integral: Measuring Light for Plants

This graph illustrates the year-round variability of global horizontal irradiance at Apogee Instruments in Logan, Utah.

 

 

As the winter solstice fast approaches, so do the shortened days and lengthy nights. In fact, I've already begun to notice that I'm coming and going from work each day in darkness. Here in Logan, Utah our latitude of 41.7° N means that by the time the solstice arrives on December 22, 2011 we'll have a solar zenith angle of 65.2°, or an angle above the horizon of 24.8°. The following graph illustrates the difference in solar radiation that northern Utah receives from winter to summer.

This time of year tends to bring a renewed challenge to my own circadian rhythm, so for me it's not hard to imagine that certain greenhouse crops and even our own nonnative houseplants are experiencing a similar effect during the winter months. Many greenhouses will provide supplemental lighting to better control the photoperiod that each crop receives. Since growth is determined by the total integrated amount of photons that a plant receives each day, this daily light integral must be measured to accurately predict plant growth. A basic quantum meter can be used to measure the instantaneous photosynthetic photon flux (PPF) in micromoles of photons per meter squared per second (µmol m^-2 s^-1), but ultimately it is the sum total of moles of photons per meter squared per day (mol m^-2 d^-1) that must be quantified.

Under constant electric lights the conversion from µmol m^-2 s^-1 to mol m^-2 d^-1 is straightforward. It is determined by multiplying the instantaneous PPF by the number of seconds in the photoperiod. One of the most highly used section of our website shows examples of this calculation: http://www.apogeeinstruments.com/conversions/daily.html.

It’s not possible to use a constant multiplier with variable lighting, so a quantum meter that has an integrating capability is necessary to determine the daily light integral under variable lighting. The Apogee MQ series meter is designed to measure and store this value each day.

{Impatiens Walleriana Photo by http://www.hear.org/starr/}

Once an accurate measurement is made it is important to interpret that measurement – it's nice to know that those impatiens are getting 10 mol m^-2 d^-1, but is this enough to grow healthy plants? There are a number of online resources available that will provide optimal lighting levels for various plants and food crops. One was developed by Jim Faust’s group at Clemson University: http://www.clemson.edu/hort/peach/pdfs/FaustHortScience2005.pdf. Another was developed by Purdue University: http://www.extension.purdue.edu/extmedia/HO/HO-238-W.pdf. Pages 5-7 include a table listing species of plants and the associated range of acceptable daily light integral values.

In the end, measuring daily light integral will help to determine the need to manipulate our environment to get high quality plant growth in the winter. It’s just too bad that I can’t walk around with my own supplemental lighting to help alleviate the long, dark winter nights.

 

Jacob Bingham
Applications Engineer

AGU 2011 Fall Meeting

Apogee is going to be at booth # 1717 at the AGU Fall Meeting 2011 in San Francisco. Please stop by and visit! You will be able to talk to our general manager, Devin Overly, or our product scientist, Seth Humphries. If you are really lucky you might even catch our company president, Bruce Bugbee, to ask any questions you might have about new products we’re developing or even our current offering.

We have been attending the AGU Fall Meeting as an exhibitor for five years. According to http://www.agu.org/meetings The AGU Fall Meeting is the largest worldwide conference in the geophysical sciences, attracting nearly 20,000 Earth and space scientists, educators, students, and policy makers. This meeting showcases current scientific theory focused on discoveries that will benefit humanity and ensure a sustainable future for our planet.

AGU was established in 1919 and officially incorporated in 1972. It now has over 60,000 members all focused toward the goal of “promoting discovery in Earth and space science for the benefit of humanity.” Our goals at Apogee have always been focused on creating innovative instrumentation for measuring climate change, improving sustainable food production and developing renewable energy. We enjoy being part of such an important work and providing the tools necessary for today’s scientists to build a better future for our world.

At this year’s show we will be exhibiting some new products. We are very excited about our new Infrared Radiometer Meter. Come over to our booth to try it out for yourself. This meter is great for everything, from monitoring canopies, to spot checking permanent infrared radiometer installations. We also are going to be showing our new product prototype of our Aspirated Radiation Shield. This product will be on sale in a few short months. The shield is designed to run on low power and will provide accurate air temperature readings in crosswinds. Come and see it for yourself, and watch for a product announcement on our Apogee blog when it is available for sale.

We will be at booth #1717 in San Francisco. See you there!

 

Whitney Mortensen
Marketing & Graphic Design

Specifications

Several years ago when our specification sheets did not include the same information they do now, a customer looked at a close-up photo of our pyranometer (with a diameter of 23.50 mm) and concluded that the sensor was the size of a dinner plate! Initially we were shocked at how someone could imagine something so preposterous. Upon closer introspection and self-examination we realized that the fault was ours in not effectively communicating information about our product.

What information should be on our specification sheets? This issue has come up repeatedly through the years at Apogee. In considering this it is helpful to keep in mind the purpose of a specification sheet. Foremost is that they are a means of communication to potential users what the product is, what it does and how it performs. Three concerns are preeminent in developing an effective specification, 1) what information should be included, 2) who is the intended audience and 3) how should the information be structured.

What information should be included? Many companies are concerned that if they are giving away too much information it could allow a competitor to reverse engineer their product. If the geometry of the product plays a role in performance, how much information should be included to communicate the dimensions of the product for a customer without releasing critical information? Additionally, what are the key parameters that are critical to potential users? We have addressed this by focusing on a detailed breakdown of how our products perform while we strive to produce the best quality products possible. While some of our products have been knocked-off, a quick examination demonstrates the difference in quality between the original and the imitation.

Who is the audience? For scientific instruments, your audience frequently ranges from Ph.D. level scientists to elementary teachers looking for tools to get students excited about science. How do you communicate the detailed information a researcher seeks without losing the interest of a more casual customer? Our specification sheets have evolved to include a photograph of the product with several brief paragraphs that describe what the product is and how it is used. This is then followed by a table, which contains detailed information on the product’s performance. Following the table is generally an illustration that shows the dimensions. This format allows someone unfamiliar with the product to first learn about the sensor. Those more concerned with detail performance can easily find that information in the table.

How should the information be presented? In 2006 Apogee advertised for a Calibration Technician/Technical Writer. We decided upon a recent psychology graduate that was looking to work while his wife finished her degree before he pursued a graduate degree in law. Ray was with Apogee for a little over a year but in that time had far reaching impacts on how Apogee communicated complex scientific ideas. Unknown to us at the time of hiring, Ray had an eye for solid design layout and composition, accompanied with detailed familiarity using Adobe Illustrator, as well as a strong work ethic. When not occupied with calibrating sensors, Ray would look over our documentation and then propose ways to communicate complex ideas with an illustration. These became integrated into specification sheets, owner’s manuals and general product information on our website and are still in use today.

Specification sheets are one more tool in effective communication between manufacturers and customers. I am excited about the direction of future communication options as advances in technology facilitate two-way communication between parties. Apogee has always sought feedback from customers and as Apogee expands marketing efforts to include social media avenues such as this blog, Facebook, and online surveys, it is our hope that our customers feel their voice is heard. Making better measurements is dependent on common understanding of what researchers are trying to measure and how Apogee can help address those needs. Effective communication, whatever the medium, can only help that process.

 

Devin Overly

General Manager

Better Know a Distributor - Campbell Scientific

The ‘Better Know a Distributor’ series highlights other companies that distribute and re-sell Apogee products.

Apogee Instruments and Campbell Scientific are more than just neighbors on the same street. Campbell Scientific has helped Apogee develop and grow in many ways. Campbell Scientific re-sells and supports most of our sensors in their weather stations. Having Apogee products included on Campbell Scientific’s price list is a testament to the quality of the products Apogee manufactures. For anyone who has wanted to know more about our great neighbor, Campbell Scientific, here is a brief history.

Campbell Scientific was organized in 1974 by Eric and Evan Campbell with initial capital from themselves, six brothers, and their father.

Eric had an interest in science at an early age. His high school science project (class of 1964) consisted of measuring the surface temperature of the moon by using an infrared sensor that he designed and built from scratch. He was introduced to making field measurements while working part time as a student at Utah State University. The research farm at the University provided an excellent environment for testing new ideas. Soon he had his own business, Logan Scientific Instruments, which produced soil psychrometers and the electronics to read them. He eventually sold his company, allowing him to finance his degree in physics with a minor in electrical engineering.

Evan became a strong asset during this time because of his interest and involvement in mechanical systems. He loved mechanical design and was pursuing a degree in manufacturing engineering.

The Campbell brothers combined their experience and education, focusing their efforts on establishing an emerging company, Campbell Scientific. Dr. Gaylon Campbell, the oldest brother and a professor at Washington State University, provided direction and help.

Campbell Scientific now employs over 200 people in their Logan offices. They sell product all over the world and have offices in Canada, France, Spain, Germany, Australia, Africa and Brazil.

Being neighbors and sister-companies with Campbell Scientific has allowed us to work together on various projects, from marketing to product development. Campbell Scientific has helped mentor Apogee through numerous growing pains and has provided valuable insight directly though formal representation on our Board of Directors as well as informally through such things as including us in their company-wide breakfasts. This way, the customers of both companies can benefit from our shared experience. Campbell Scientific is a great company to work with, and we are definitely glad that they are our neighbors.

Sources:
www.campbellsci.ca/Download/CorpProf.pdf

 

Whitney Mortensen
Marketing & Graphic Design

Accelerated Aging

I work hard and take pride in doing good work: to always do my best. As I have come to be part of the Apogee family, I have noticed that my feelings of hard work and pride are commonly shared. I have seen others work on weekends, or late into the evenings to ensure that our products are both accurate, rugged and ship on time. Collectively, we want Apogee to sell the best products and have the best reputation.

One type of product in which we at Apogee take particular pride is our short-wave sensors; i.e. pyranometer and quantum sensors. These rugged, optical sensors can withstand harsh outdoor environments, submersion in salt water, and are vibration tolerant. Yet, this is not enough for us.

We perform accelerated aging tests on our sensors to provide confidence in their long-term stability. Accelerated aging tests cannot directly predict the product lifetime in the field, but they do provide assurance that the product is rugged enough to withstand expected operating conditions. Accelerated aging tests often involve high levels of UV light, high temperature and humidity, high vibration, or some combination of extreme conditions. In this case we used extreme temperature cycling. We cycled a group of sensors every three hours from -20 to 60 C (-4 to 140 F). After 3 months, and more than 350 temperature cycles, the sensors did not fail.


Although our sensors are rugged, we recommend periodically, minimally every year, checking the output of radiation sensors against the sun on clear days using our free Clearsky Calculator. The user enters the location of the sensor (longitude, latitude, time zone) as well as day of year and environmental conditions and an expected output of the sensor is calculated. The sky must be clear. Our experience is that the calculated radiation intensity is within 2% of the actual solar intensity. If it does not match, the user should re-clean and inspect the sensor and again check against the Clearsky Calculator. If it still does not match then please give us a call and we can help resolve issues and, if necessary, help you get it recalibrated.

We want to ensure that we have a sensor that will continue to operate whether continuously submerged, frozen in arctic conditions or heated under the tropical sun.

Seth Humphries
Product Development Scientist