FAQs

Apogee’s customer service is available 8 AM – 5 PM MT, Monday through Friday. View our special closures here.

We recommend sensors be recalibrated every two years for maximum accuracy. That being said, you may wish to wait longer between recalibration cycles depending on your requirements, data accuracy, and usage. The Clear Sky Calculator may be used as a reference to determine if recalibration is necessary for pyranometers and quantum sensors.

Get the full rundown on pricing, process, get started on a recalibration request, and more here.

We have a 30-day return window and a 4-year warranty on most products. Fill out an RMA form to begin the return or repair process, and our RMA team will contact you.

• Visit your product manual; Near the end, there will be a troubleshooting section to help with common errors.
• Visit the product’s specific FAQs on its support page.
• Reach out to our technical support team! They are happy to answer questions, troubleshoot, and brainstorm solutions for your specific situation. Email them at techsupport@apogeeinstruments.com or call them at +1(435)245-8012.

Yes! However, it’s best if you order before coming into our location so that we can have the product ready when you get here. Instead of ordering online, email sales@apogeeinstruments.com or call (435)245-8012 to place your order and arrange its pickup.

We send out an email to alert our customers of product and process updates, lead time changes, and more. Sign up here if you would like to receive those updates.

We attend many tradeshows every year all around the world. View our tradeshow list to see if we will be at one near you or if you’ll be attending the same show as us. Stop by our booth or reach out to our team at techsupport@apogeeinstruments.com to arrange a meeting.

At Apogee, our solar radiation sensors have a specification for accuracy, uniformity, and repeatability. The accuracy compares each sensor’s output to an absolute reference standard. Uniformity is how consistent our sensors are compared to each other. Repeatability refers to how consistently a sensor performs against itself. The numbers in our specifications are based on statistical analysis. Large populations of our sensors are compared to a reference, ISO or NIST traceable where available, and the error is measured. We then calculate the mean and standard deviation of the sample from the reference standard. The specifications listed for accuracy, uniformity and repeatability represent plus or minus two standard deviations from the mean (95% of the population). Click here for a knowledge base article on sensor specifications.

Photosynthesis and plant growth depend on the energy in radiation, but only specific wavelengths of radiation cause photosynthesis. We have known since Einstein that one photon excites one electron (the Stark-Einstein Law), which starts photosynthesis. In 1972, a scientist named Keith McCree showed that a meter that counted the number of photons in radiation would more accurately predict photosynthesis than the previously used foot-candle meters. LI-COR (Lincoln, NE) started making meters to measure this radiation and scientists quickly switched to the new measurement system, which is called Photosynthetic Photon Flux (PPF). The energy in a photon is called a quantum so these meters are called quantum meters. A quarter century later, LI-COR has sold thousands of high quality meters, but their least expensive quantum meter with sensor costs $780. The high cost means that they are used only by scientists and large commercial growers. Smaller growers have continued to use foot-candle meters, which measure light for humans. Footcandle meters have errors of up to 45% when used to measure light for photosynthesis.

Solar radiation is a term used to describe visible and near-visible (ultraviolet and near-infrared) radiation emitted from the sun. The different regions are described by their wavelength range within the broad band range of 200 to 100 000 nm (nanometers).

Terrestrial radiation is a term used to describe infrared radiation emitted from the earth. The components of solar and terrestrial radiation and their wavelength ranges are:

Ultraviolet	250 to 400 nm	UV sensor or spectroradiometer
Visible	400 to 700 nm	Quantum sensor or spectroradiometer
Near Infrared	700 to 3000 nm
Infrared	3000 to 100 000 nm	Infrared radiometer

Approximately 99 percent of solar, or short-wave, radiation at the earth's surface is contained in the region from 300 to 3000 nm while most of terrestrial, or long-wave, radiation is contained in the region from 3500 to 50 000 nm.

Outside the earth's atmosphere, solar radiation has an intensity of approximately 1370 watts per square meter. This is the value at mean earth-sun distance at the top of the atmosphere and is referred to as the Solar Constant. On the surface of the earth on a clear day, at noon, the direct beam radiation will be approximately 1000 watts per square meter for many locations.

The availability of energy is affected by location (including latitude and elevation), season, and time of day. All of which can be readily determined. However, the biggest factors affecting the available energy are cloud cover and other meteorological conditions, which vary with location and time.

Historically, solar measurements have been taken with horizontal instruments over the complete day. In the Northern US, this results in early summer values 4 to 6 times greater than early winter values. In the South, differences would be 2 to 3 times greater. This is due, in part, to the weather and, to a larger degree, the sun angle and the length of daylight.

µmol m^-2 s^-1 to footcandles

µmol m^-2 s^-1 to Lux

µmol m^-2 s^-1 to mol m^-2 d^-1

µmol m^-2 s^-1 to Einsteins

µmol m^-2 s^-1 to Watts m^-2 when measuring UV light in sunlight

PPFD to Illuminance Calculator

External Conversion Sites:
Environmental Growth Chambers (EGC) has a comprehensive table and calculator to approximate conversion values for radiation from 400-700 nm from different lamp types.