Flipping the Switch Converting From HPS to LED Lights

Professor DeBacco

Gavita Guide
Paper
https://gavita.com/retail/5-tips-for-...
Webinar on YouTube
Hawthorne. (2021, December 16). Converting from HPS to LED: Key Considerations (webinar recording). YouTube.    • Converting from HPS to LED: Key Consi...  
Transcript: https://www.hawthorne-gardening.com/e...

Keep In-Mind
This is from a lighting manufacture that sells both HPS and LED lights, but is providing this information to help growers make the switch.

5 Tips for a Seamless Transition from HPS to LED
Adjust temperature when growing with led
Use VPD as your management tool
Factor in HVAC and dehumidification
Consider the effects of light spectra and light intensity on crop growth
Monitor and adjust nutrition and irrigation based on transpiration
Change in Temperature when Growing with LED
HPS lighting produces a high amount of heat while many growers consider this to be a “waste” radiant, but it does help heat the leaf surface.

This drives the transpiration of the plant which is the plants movement of water (and nutrients) through the plant.
Leaf Temperature Comparison
This graph quantifies the difference in temperature of the leaf surface under LED lights or HPS lighting.

HPS produces more infrared (700-850nm) which results in the heating of the leaves.
LED Can Shift the Room Temperature
Growers should get an infrared temperature sensor to know what their current leaf temperatures are.
Take a random sampling as the plants are growing and record the results.

This data can be used to adjust the ambient temperature of the growing environment after the installation of LED lights to match the previous plant conditions.

Note: This impacts the VPD (Vapor Pressure Deficit)
Use VPD to Manage Growing Environment
Air can only hold a certain amount of water vapor at a given temperature before it starts condensing back to liquid water (in forms such as dew or rain).

Adjust HVAC and Consider Dehumidification
Remember that LED’s still produce heat

LEDs just produce more light per watt than an HPS
To get the same light it takes less heat

Often this reduction in heat from the lights, but with an increase in room temperature, there will be less demand on the HVAC system.

This can result in compensation with a dehumidifier.

So the light fixtures may be a 1:1 change, but there may be more supplemental equipment (such as a dehumidifier) that is needed.

Measure of the light intensity

Taken at canopy level as the plants were growing

LED lights are providing a more intense light at the canopy level.

This can result in an increase in bud yield.
Room Layout and PPFD and Uniformity Comparison
Essentially a 1:1 conversion of the fixtures in physical space in the grow room.

Light Intensity
Since LEDs emit less radiant heat than HPS, cultivators can increase the PPFD, (or the amount of plant-usable light, measured in photons) to higher levels than recommended when using HPS.

This can be especially advantageous when carbon dioxide supplementation is being utilized in a grow room.
Data Driven Changes to Nutrient and Irrigation Based on Transpiration
Know what the baseline is for your current system, as this is what you will be adjusting from.

Cost Savings?
This can be harder to determine as there are often rebates which are great, but often vary across different regions and are not always the same.

Fixture upfront costs and changes to HVAC systems need to be taken into consideration in addition to the energy consumption to run the lights.
Grower Suggestions
Going to LED lighting needs to be a complete grow room commitment

Changing out failed HPS lights to LED (despite there being a 1:1 coverage area comparison) is not advised due to the different plant and environmental impacts.

Currently HPS is the overall more cost effective option
Since you can get more than six HPS lights for the cost of one LED light fixture

This cost difference can buy a lot of electricity and bulbs.
Lighting Going Forward
LED technology is the technology of the future and it is currently available, but is cost prohibitive for many.

As with any technology there will be improvements and reduced cost.
Ex. Customizable plant spectrums

Once the cost of initial purchase drops it will make for an easier switch for growers to make.

As you have seen it is more than just simply changing out the fixtures.

So, it may be worth it to wait a little longer if you currently have an effective HPS set-up.

Link to Lecture Slides: https://drive.google.com/file/d/1lfRi...

*Due to the description character limit the full work cited for "Flipping the Switch Converting From HPS to LED Lights" can be viewed at... https://docs.google.com/document/d/1l...