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Temperature and Humidity: Difference between revisions
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→Vapour pressure deficit (VPD): Headings
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VPD is a metric (unit kPa) to measure the difference (deficit) between how much water there is in the air (AVP) and the maximum amount of water the air can currently hold (SVP). It is a more accurate way of measuring the "dryness" of air that takes into account air temperature, leaf temperature and air humidity. VPD directly correlates to rate of [[Plant processes#Transpiration|transpiration]]. Cannabis should be exposed to between 0.5 and 1.6kPa. Fluctuations in VPD over 0.5kPa can decrease yields by up to 20%. <ref>Minimizing VPD Fluctuations Maintains Higher Stomatal Conductance and Photosynthesis, Resulting in Improvement of Plant Growth in Lettuce, 2021 Inoue - https://doi.org/10.3389/fpls.2021.646144</ref>
An excellent VPD calculator and chart of ideal VPD for each [[Life Stages|life stage]] can be found at [https://www.dimluxlighting.com/knowledge/vapor-pressure-deficit-vpd-calculator/ dimluxlighting.com]▼
VPD can be calculated by using the [[wikipedia:Tetens_equation|Tentens Equation]] to find the vapor pressure in the leaf and vapor pressure in air, and then subtracting the vapor pressure of air from the vapor pressure of the leaf. e.g.▼
[https://www.cannabissciencetech.com/view/circular-cannabis-systems-tracking-and-minimizing-waste-and-emissions-impacts More on VPD]<ref>L Breit, M Leavitt, A Boyd, Cannabis Science and Technology 2(2), 52-61 (2019). https://www.cannabissciencetech.com/view/circular-cannabis-systems-tracking-and-minimizing-waste-and-emissions-impacts</ref>▼
===== '''vapor pressure in the leaf''' = 0.61078 * <big>''e''</big><sup>17.27 * T / (T + 237.3)</sup> Where T is the leaf temperature in Celsius. If leaf temp is unknown air temp can be used. =====▼
'''vapor pressure of air''' = RH * 0.61078 * <big>''e''</big><sup>17.27 * T / (T + 237.3)</sup> Where T is air temperature in celsius and RH is relative humidity.▼
==== Calculating VPD ====
'''VPD''' = '''vapor pressure in the leaf - vapor pressure of air''' ▼
▲VPD can be calculated by using the [[wikipedia:Tetens_equation|Tentens Equation]] to find the vapor pressure in the leaf and vapor pressure in air, and then subtracting the vapor pressure of air from the vapor pressure of the leaf. e.g.
▲
▲An excellent VPD calculator and chart of ideal VPD for each [[Life Stages|life stage]] can be found at [https://www.dimluxlighting.com/knowledge/vapor-pressure-deficit-vpd-calculator/ dimluxlighting.com]
▲'''vapor pressure of air''' = RH * 0.61078 * <big>''e''</big><sup>17.27 * T / (T + 237.3)</sup> Where T is air temperature in celsius and RH is relative humidity.
▲[https://www.cannabissciencetech.com/view/circular-cannabis-systems-tracking-and-minimizing-waste-and-emissions-impacts More on VPD]<ref>L Breit, M Leavitt, A Boyd, Cannabis Science and Technology 2(2), 52-61 (2019). https://www.cannabissciencetech.com/view/circular-cannabis-systems-tracking-and-minimizing-waste-and-emissions-impacts</ref>
==Ideal conditions==
The ideal temperature is range is 24°- 28°C<ref>Chandra et al. (2008) - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3550641/pdf/12298_2008_Article_27.pdf</ref> while the ideal humidity is 40-60%. Ideal VPD is around 1 kPa <ref>Nadia Sabeh, PhD - Vapor Pressure Deficit (VPD) and Cannabis Cultivation -
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