Plant growth obviously relies heavily on lighting conditions, and with increasing reliance on artificial lighting, test and characterization is mission-critical to yield and productivity managment. Wading through the specifications of lamp and LED light source manufacturers can be challenging. Is the light source with the highest LUX value the best bet? What about PAR? What is PPFD?
LUX is the SI derived unit of illuminance and luminous emittance. It is measured in luminous flux per unit area, and 1 lux equates to one lumen per square meter. This is the unit of measure related to the intensity of a light source as perceived by the human eye. Many lighting manufacturers quantify the output of their sources in this unit of measure, but it is not necessarily a good comparison value in horticultural applications. The reason is actually quite simple; is photosynthesis in plants, a function of light intensity as perceived by the human eye? No. Photosynthesis in plants -- is function of the light intensity that matters to plants. A good example is green light, to which the eye is has the greatest responsivity. Plants, on the other hand, have much greater responsivity to light in the blue and red portions of the spectrum, where chlorophyl absorption is greatest.
The light intensity that matters to plants is known as PAR, or photosynthetic active radiation from 400 to 700 nm in wavelength, an is measured in units of PPFD (Photosynthetic Photon Flux Density). Many suppliers of horticultural light sources therefore specify output in terms of PAR. Unfortunately, this can also be somewhat misleading, as chlorophyll absorption is higher in the blue and red portions of the spectrum. As a result, two light sources could have identical PAR output, but deliver significantly different performance, depending on the spectral content within the PAR range. This makes it important to know PPFD values in the blue, green and red portions of the spectrum.
Other important lighting values including parameters such as Spectral Power Distribution (SPD), Peak Wavelength, and total Irradiance over the PAR range. The ability to log these values versus time, lighting distance or position relative to the source is also important.
Gamma Scientific offers the fully loaded light measurement solution for horticultural lighting test and characterization, the MK350S Premium. We also have an extensive track record in the design and installation of fully integrated, facility-wide light measurement and monitoring solutions.