For the measurement of the total amount of PAR radiation available a PQS 1 sensor is often used. However, for certain applications, for example when LED’s are used as the light source, more in-depth knowledge of the spectral composition of the radiation is required.
A second factor of importance is that many crops have an optimal yield at a specific ambient temperature. The temperature is driven by changes in solar radiation and the thermal infrared radiation exchange. This energy balance is measured by net radiometers.
In 2010 three Dutch companies - Croppings, Beemster Trading and Avantes - developed the HortiSpec+, a novel instrument combining both spectral and net radiation measurements. The instrument is based on a spectral radiometer sensitive to wavelengths between 200 nm and 1100 nm with a 0.5 nm resolution, and a single component broadband net radiometer with a measurement range between 200 nm and 100 µm. This HNR 1 net radiometer is based on the NR Lite2 and specially adapted for this application by Kipp & Zonen.
The HortiSpec+ provides spectral measurements of PAR, radiation intensity, several wavelength ratios and the total net radiation balance. The main benefit of combining spectral and net radiation measurements is that it gives vital information on several parameters for crop optimization, especially when growing fruit, vegetables and flowers in greenhouses. Lighting within greenhouses needs to be carefully controlled to achieve the best yield and quality.
Accurate measurements provide information on the amount of energy from both the sun and lamps that is received by plants inside the greenhouse and decisions can be made to close sun blinds or dim lights. If the net radiation changes significantly a temperature change can be expected to follow. This can then be anticipated by controlling the heating system.
For greenhouses energy is a major part of the total production costs. A study at the University of Applied Sciences Den Bosch has shown that by using the data from the HortiSpec+ as an input for greenhouse climate control systems, energy savings from 10 % to 20 % are achievable.
Spectral measurements of solar radiation and PAR in particular, also have applications in the fields of agronomy and forestry. For example, accurate measurement of the spectral distribution of PAR and the ratio of blue to red, and red to far-red, wavelengths provides a deeper knowledge of the solar radiation available for plant development both above and below forest canopies.
For more information on the HortiSpec+ please contact Mr. Jos Beemster of Beemster Trading at www.hortispec.nl (in Dutch) or translated through Google.