Before the revival of Light-Emitting Diode (LED) technology, measuring and comparing lights for indoor cannabis cultivation was an easy and straight forward process. Like most of the horticultural industry, cultivators typically used High-Pressure Sodium (HPS) or Metal Halide (MH), and light intensity was measured by energy output generally for flowering, ranging from around 400
Much has been written about the intelligence of plants. As far back as the 19th century, German chemist Justus Von Leibig remarked that “Plants search for food as if they had eyes”. Notably, plants can detect the quality, quantity and direction of light – and light is crucial. This should certainly be considered when trouble shooting the problem of intermittent hermaphroditism.
A major consideration to the cannabis cultivation world is the use of grow room cameras for monitoring or security. Whether or not security cameras emit enough photons at the right wavelength to interfere with a plants photo-perception is not something this article lays claim to, however the question was put to me and in this context, it allows for a wider discussion on red light and near-infrared photoreceptors – the phytochromes.
The table below illustrates the wavelength of light which may act upon the numerous photoreceptors found in plants. The photoreceptor known as Phytochrome-B (PhyB) detects light from the red and far-red spectrum. PhyB activation has been proven under experimental conditions to be a necessary trigger for various processes, including flowering, photoblasty, and other biological pathways. The use of certain cameras in the plant’s environment must therefore be carefully considered, as detection of light during the dark phase is a cause of unplanned hermaphroditism.
Now the costQUALITY – PhyB optimally absorbs light between 650-750nm, although some activation may occur up to 790nm. PhyB can reversibly switch between red (Pr) and near-infrared (Pfr) perception and this switch allows interaction/disassociation with PIFs (Phytochrome Interacting Factors – these are transcription factors that control the regulation of other genes, amongst other things). Pr to Pfr conversion induces morphogenetic changes which are undone by Pfr to Pr conversion (Salome et al., 2002). Moreover this re-configuration allowing the capture of red vs near-infrared can happen within seconds, can occur hundreds of times, and shows no signs of toxicity to the cell or drop in efficiency (Levskaya et al., 2009). The activation of PIFs can cause flowering responses, interfere with circadian signalling and may even have a role in immunity. It is therefore recommended that unwanted red light receptor activation is avoided and security camera infrared output is reviewed, and ideally, light emission should be above 800nm.
In fact, proper comparisons between HPS and LED have also been sorely lacking in the peer-reviewed literature. There are still, QUANTITY – Plants can detect very low levels of light, but light intensity correlates with the number of photoreceptors activated, therefore very low output/low intensity can have minimal to no effect on the plants. As the distance between the plant and the light source correlates with intensity, it is advised that, in addition to the camera’s output, we also ensure the distance from the camera to the plants is as great (far) as possible. In addition, should the camera use multiple infrared LEDs, try to adjust these, or alternatively, find a brand of camera which can be adjusted, or emits light above 800nm.
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