HPS LED or Hybrid? What does it mean for your VPD?

We tackle the different approaches to lighting strategies using HPS, LED and Hybrid configurations. The setup considerations and trade-offs for HVAC and Dehumidification.
In our office, we conducted an experiment to understand the effect of temperature on canopy growth. We grew four different types of basil under uncontrolled ambient conditions and compared the results. Our findings suggest that for production, a HPS or a hybrid LED HPS configuration would be most effective due to the forward-throw heat to the canopy.
Vapor Pressure Deficit is critical to optimizing plant growth and development. We look at the varying effects of lighting sources on leaf surface temperature (LST) and how they affect the calculation of your VPD.
Reach out with questions at SustainableTerrains.com or GandyGrows.com

[@kenthomas8181]

Great video can't wait to see more like this!!!!.... OATMEAL MUSIC 🎶

[@gandygrows]

Yeah Man! Got several more fixture videos in the chute. Thanks for watching KT!

[@aworldsdeath]

Doesn't reducing the wattage of the HPS create more heat and a different light spectrum (more than 1500K difference) than it's designed to run? A 1000w bulb is meant to run at 1000w - Turn it up and raise the light to the desired level and you may find better results.

[@gandygrows]

You are correct. This was for demonstration purposes only. HPS prefer to be fired and operated at full power for optimum spectrum and performance

[@zkilla4611]

Simply need less AC for LEDs in warm climate at least.

[@gandygrows]

If you have humid fresh air, yes. If you have to add Dehus to compensate for the added transpiration rate, you are effectively adding heaters. In a hybrid configuration, in extreme heat situations, you can toggle off the HPS to keep temps in range.

[@zkilla4611]

@@gandygrows I'm in a hot Humid climate area. So AC has to run 24/7. But I have to use a dehumidifier also to keep the dam humidity in check. It is what it is. But I will say I'm getting great results. VPD is all over the place because of the fluctuation. My plants seem to like it tho.

[@gandygrows]

@@zkilla4611 Hot and Humid are best LED applications. Plant canopy needs to stay warm and humidity needs to not get too low. Too high of RH is always an issue. Not sure what scale you are on 200 sq ft or 20K sq ft facility, but look in to CannabisMechanical's setup on IG. You can trick a mini split with a heat pump to do both, cool and remove humidity. If you hang Quests or Andens, they are essentially just heaters. I'll do more deep dives on this nuance of the topic because I am still learning the difference between latent and sensible loads and heat, re-heat and dehu etc.
The initial point to make is that if you take an HPS facility and just swap out 1:1 for LED, you will have issues with too much humidity when removing the Heat from the HPS. Also the heat from HPS heats the canopy directly whereas and LED facility you have to control the Leaf Surface temperature with your ambient temperature, not the IR light from the light source.
I've heard a ballpark number of no more than .4 VPD differential bandwidth if possible. A little positive stress is generally good for crops, but when you have high RH or VPD swings, thats when you get condensation, mold or PM issue conditions. If your HVACD can keep up with all the moisture, keep pushing those plants until you can't hold your bandwidths or you'll have issues.
Hope this answered some or part of your question!

[@smithr1974]

1st

[@gandygrows]

Nailed it!