Radiometry, which is the measurement of electromagnetic radiation, is critically important for various environmental research works and can be applied for developing illumination sources for industrial and commercial use. Photometry is the measurement of radiometric sources as well as their interaction with the human eye. Spectroradiometry is the measurement of absolute radiometric quantities across particular wavelength bands.
.jpg)
The wide range of spectrometers and accessories offered by Avantes support even the most challenging photometric and spectroradiometric measurements. Avantes instruments are trusted globally for their applicability for measurements of radiometric sources such as the sun, commercial and residential lighting, UV germicidal sources, and solar simulator. This article investigates real-world applications for radiometric measurements.
.jpg)
AvaSpec-ULS3648
.jpg)
AvaSpec ULS2048x64
.jpg)
AvaLight-DHc
.jpg)
AvaSpec-SolarXM
*North America only
What is Radiometry?
In principle, radiometry concerns the measurement of the electromagnetic wave or radiations produced when photons oscillate. The amount of energy carried by the photons, and in turn the “color” of the radiation, is determined by the frequency of these waves, or the wavelength. The complete electromagnetic range extends from X-rays to the deep UV, through the visible light spectrum, and to the far infrared (IR) and further into microwaves and radio waves. Radiometric measurements in the UV, visible light, and the near-IR from 250 to 2500 nm are supported by Avantes instruments.
Radiometric data collection is achieved with a detector in a spectrometer collecting photons and converting them to an electrical charge based on a known relationship. Radiometric quantities, such as those specified in the table below, can be determined by calibrating the spectrometer against a reference source from NIST/PTB or other standards body in such a way that the response of the detector is correlated to this absolute standard.
| Radiometric Unit |
Symbol |
Definition |
| Radiant flux |
Φ |
The total optical power emitted from a source. |
| Irradiance |
E |
The flux per unit area striking a surface. |
| Intensity |
I |
The flux per unit solid angle from a source. (often confused with irradiance or radiance) |
| Radiance |
L |
The flux per unit solid angle, per unit projected area from an extended source. |
| Luminous Flux (Lumens) |
Φv |
Perceived power from a source weighted to the sensitivity of the human eye |
What Do Radiometric Units Reveal?
Radiometric units can be used to give a complete account of the power of sources such as the sun, LEDs, light bulbs, and so on. This is vital since the sensitivity of any radiometric measurement system could vary depending on the variations in all the components such as optical components and the detector. The process of calibration enables the absolute standard to be referred to derive calibrated radiometric units. Examples of radiometric measurement applications can be found in quite a few research projects and industries.
Baseline Surface Radiation Network (BSRN)
The Baseline Surface Radiation Network (BSRN) is a project of the World Climate Research Programme (WCRP) — the international body organizing climate research across the planet. BSRN is a network of over 60 manned sites that fulfill program standards, and data from this network is gathered at the World Radiation Monitoring Center, hosted now at the Alfred Wegener Institute in Bremerhaven, Germany.
.png)
NASA Langley Research Center BSRN site
The goal of the BSRN program, which was set up in the late 1980s, is to create a substantial historical record of long-term variability in radiative load across the globe in tandem with internationally agreed-upon standards as well as instrument calibration procedures. This data on surface radiation is used for various applications such as monitoring changes in radiation flux over time, providing validation for satellite-based radiation estimates, and developing high-quality computational models used by scientists to forecast climate response.
A monitoring installation or participating observatory can apply for gaining recognition as a BSRN site by fulfilling various institutional and geographic prerequisites, such as the validation of radiometric instrumentation traceability of calibrations to meet global standards.
The Tartu Observatory in Tartu, Estonia, which was originally set up in 1810, is a recognized BSRN site. For a period of three years, this observatory performed an exploratory investigation of a radiometric system equipped with an Avantes spectrometer for narrow-band continuous computer-assisted spectrometry. The system gathered a spectral measurement once in 15 minutes, recording the ratio of UVA to UVB, radiation spectral irradiance at 306 nm, and erythemal UV Index (UVI). The installation was broadly examined and scientists reported results that were comparable to those achieved by using filter instruments and with LibRatran (Library of Radiative Transfer) codes at the Tartu site.
Recent advancements in CMOS technology have enabled the most recent Avantes instruments for radiometric measurements to achieve better dark noise performance and ultra-low stray light when compared to previous models.
Pandora Spectrometer System
The goal of the Pandora program, which was established in 2005, was to develop a wide range of low-cost, high-quality spectrometers that can be distributed in huge quantities to measure air quality as well as to validate satellite measurements of the atmosphere. One of the exceptional attributes of the Pandora systems is their potential to record total column profiles of the atmosphere, measuring all the layers at the same time.
A Pandora spectrometer unit is comparatively small and portable, enabling these systems to be set up in installations across the globe from Finland and Thessaloniki to the University of Alaska and atop the NOAA station in Boulder, Colorado. A specially designed version can also be set up on a marine vessel even under moderate seas with the help of software that corrects for motion to maintain the sun centered toward the field of view. The spectrometer central to the Pandora system is the Avantes AvaSpecULS2048x64 back-thinned CCD spectrometer.
Real-World Practical Lighting Applications
In the Fishing Industry
Many types of sea-life and fish are phototaxic, that is, they move toward lights. This effect has been perceived well, and through the years, different types of light sources for fishing have been created. Metal-halide lamps, which pushed halogen and incandescent lamps back, delivered the high light intensity needed to lure fish; however, power consumption was increased exponentially. Moreover, these lamps generate UV radiation that is hazardous to fishermen.
.jpg)
Squid-fishing vessels, Tsuyazak Fishing Port
Scientists at the Korea Maritime University in Busan, Korea, have been working with LED light sources to create an alternative light source that operates in a highly efficient manner — and is, hence, more cost-effective — and does not produce hazardous radiation. In their study, they investigated the impacts of wavelength and intensity on the behavior of squid with the help of the AvaSpec-ULS3648 spectrometer to characterize the performance of the light sources under review.
The scientists identified that the squid under study reacted the most to light in the blue spectrum, from 450 to 490 nm, penetrating sea water the most. However, multiple LEDs were required for matching the intensity of the single metal-halide lamp at 1.5 kW. In the final system, six blue LED modules were used, which consumed 180 W of power. This is one-eighth the power requirements of the MHL, and the weight of the system is one-seventh of that of the MHL.
Hydroponic Farming
In various parts of the world, indoor farming is being increasingly adopted; however, these systems incur high investment costs for design and installation. Scientists from the Chinese Agricultural University, Beijing, analyzed the growth response of hydroponically grown lettuce under changing photoperiod, light intensity, and light quality conditions.
.jpg)
Indoor farming in the Netherlands
The experimental setup included four settings for Photosynthetic Photon Flux Density (PPFD) at 150, 200, 250, and 300 µmol/m2*s and three changes in light quality with the help of fluorescent bulbs at red:blue (R:B) ratio of 1.8 and LED sources at R:B 1.2 and 2.2. Eventually, the scientists also altered the photoperiod between 12 hours/day and 16 hours/day. The daily light integral (DLI) for each set of parameters was determined by the researchers. These parameters were rigorously controlled and measured throughout with the help of an Avantes spectrometer system available in China, but on par with the AvaSpec-ULS2048CL-EVO.
Solar Radiometry
In the solar system, the sun is the major source of all energy, yet it is also a source of hazard. Huge explosions, called solar flares, take place in the top layers of the sun, expelling ionized radiation into the universe. In case the earth lies in the direct path of a large-scale coronal explosion, it could be catastrophic for the humankind, leaving several of the modern conveniences unusable.
Astrophysicists, physicists, and astronomers are still in the process of investigating the complicated electrochemical reactions and plasma characteristics of the sun and its various layers. Solar researchers got a unique chance to study the sun’s corona when the Great North American Eclipse crossed the United States in 2017. Avantes was accessible at the National Center for Atmospheric Research (NCAR) observation base in Casper, Wyoming.
Solar Simulator Characterization
Solar simulators are used by solar panel manufacturers to control the quality of their products for quantum efficiency. The ASTM method 927-05 provides an elaborate description of the characterization of solar simulators. Avantes instruments and systems support the ASTM method for continuous or pulsed wave solar simulators. The AvaSpec-SolarXM spectrometer bundle and software suite, available for the North American Market, are remarkable.
Avantes Radiometric Instruments
Avantes is trusted across the globe to enable near real-time radiometric measurements for applications varying from agriculture to semiconductors, with a wide range of light sources, modular spectrometers, and accessories. Support for any unique application can be availed from Avantes through consultation with a knowledgeable Sales Engineer or trusted Avantes distributor.
References and Further Reading
- Ansko, I., et al. “Study of Suitability of AvaSpec Array Spectrometer for Solar UV Field Measurements.” Atmospheric Chemistry and Physics 8.12 (2008): 3247-3253.
- Choi, J. S., et al. “Photoreaction analysis of squids for the development of a LED-fishing lamp.” Proceedings of the 2nd international conference on maritime and naval science and engineering. 2009.
- Kuusk, Joel, and Andres Kuusk. “Hyperspectral radiometer for automated measurement of global and diffuse sky irradiance.” Journal of Quantitative Spectroscopy and Radiative Transfer 204 (2018): 272-280.
- Zhang, Xin, et al. “Effects of environment lighting on the growth, photosynthesis, and quality of hydroponic lettuce in a plant factory.” International Journal of Agricultural and Biological Engineering11.2 (2018): 33-40.
This information has been sourced, reviewed and adapted from materials provided by Avantes BV.
For more information on this source, please visit Avantes BV.