Making the Switch from HID to LED Grow Lights

By Mike Howard
Published: May 10, 2021 | Last updated: May 26, 2021 05:23:01
Presented by Fohse
Key Takeaways

As LED grow lights become more powerful, reliable, and energy efficient, more and more commercial and home cultivators are making the switch from HID to LED. To some this switch is easy, and to others it may be a bit harder. Mike Howard has compiled a list of common differences between the systems, and some actionable advice to help make the transition a bit smoother.

Source: IG Keene.Media

Cultivators all over are making the switch from high intensity discharge (HID) to light emitting diode (LED) grow lights.

While we can attribute some of the attention to technological advancements in LED lighting, growers have also come a long way in learning how to adapt their plants and environment to growing with modern LED fixtures.

If you grow cannabis, you know that light is vital to the health of your plants and eventual yield. With a few of the following factors in mind, cannabis grown under LEDs can significantly exceed (in yield and quality) those produced under traditional HID lights. Let’s dig in.



The biggest and most notable factor to take into consideration when switching from HID to LED is temperature. Typically LED grow rooms are run several degrees warmer. LED grow lights also produce far less radiant heat than traditional HID lighting, leading to a higher ambient temperature needed in LED growrooms.

Every LED room that I’ve run has been within the 82-85 degree temperature range for the majority of the timeframe. This actually gives plants the added benefit of a much more even, gentle temperature gradient throughout the canopy since extreme heat no longer has to be combated with extreme air conditioning.


With higher temperatures comes higher humidity to make sure your VPD (vapor-pressure deficit) is still on point. An LED room run at 82-83 degrees will need a higher humidity, while an HID room run in the 70s will need a lower humidity to maintain an adequate VPD.

Sometimes you will see negative feedback loops with HID created from the abundance of heat put off by the fixtures. This excess heat creates the need for more cooling, which in turn cools and dries the air removing the humidity. This is a reason HID rooms typically need more cooling, and LED rooms sometimes need more dehumidification.



Higher humidity and higher temperatures lead to an increase in the amount of water and nutrients the plant will need. Increasing the frequency of watering or the volume given is something that needs to be done incrementally as the intensity of the light is increased.

You may also find that your plants need more nutrients, so keep an eye on any deficiencies that may arise and adjust your feeding regiment accordingly.

Indoor commercial cannabis growLED grow lights have the ability to control the spectrum and therefore manipulate plant morphology. [photo credit: IG]


Most LED lights will be equipped with a control that allows you to increase or decrease intensity so you can slowly acclimate those plants to higher light levels. I recommend going up in intensity slowly while increasing CO2 and EC in conjunction as the plant is being pushed to its limits. If any stress factors are noticed while increasing intensity, scale back for a day or two and reevaluate if you need to increase your EC or if your plant is at the max light levels it can handle.

(Read also: How Minerals and Light Affect Terpene Production)

Most cultivars I have encountered can take PPFD levels over 1,200 and some upwards of 1,500 if acclimated correctly, however some cultivars are a bit finicky and will not take higher light levels. If you have the ability to increase or decrease intensity to each cultivar that is ideal, however if you only have one controller per room I recommend grouping plants that are able to take higher light levels together so you are able to push them to their max potential without negatively impacting other cultivars that can’t handle such intensity.



Being able to change the spectrum is something new for those stuck under a high pressure sodium (HPS) bulb the last few decades, so let’s go over some general guidance on LEDs that have the ability to control the spectrum, and therefore manipulate plant morphology.

Typically higher end LED fixtures like the Fohse A3i will give you the ability to change spectrums that simulate seasons like Spring, Summer, and Autumn. The Spring spectrum is recommended during veg and the beginning of flower and will typically have a higher concentration of white and blue light, with less red and far red. Summer spectrum is recommended after the first 2-3 weeks in flower as it has a higher concentration of intensity of red spectrum.

If you increase the amount of red spectrum during the first 2 weeks of flower you will see more stretch and internodal spacing. While you generally switch over to Autumn anywhere between weeks 5-6. This spectrum can be used all the way until the end of harvest.

Some growers will switch back to Spring spectrum for the last week or so in an attempt to boost terpene and cannabinoid levels. Feel free to experiment and see what works best with the cultivars you grow or depending on the final product being made from the plant.

Cannabis plant under LEDsCannabis plants can grow taller under LED grow lights. [photo credit: IG]


Grow Bigger

A traditional setup in a single tier facility under HID lighting plants can only be grown to a certain height depending on the height of the fixtures. One of the main reasons for this is the excess heat produced by HID lighting will negatively impact volatile terpenes and cannabinoids if grown too close to the fixture. Under LED grow lights the plants can be grown taller, as the heat emitted is far less intense.

Go Vertical

With less radiant heat LED grow lights have paved the way for the ability to go vertical and maximize indoor space and crop yields.

This style of farming has permeated herbaceous crops and cannabis rapidly. Some vertical farms boost production by 10-100 times more per acre while using up to 90% less water. The cannabis industry has taken note and vertically tiered facilities have increased in popularity and continue to be dialed in to increase efficiencies as this method is refined and perfected. 2-3 tiered facilities and even facilities with 5+ tiers are popping up and growers and investors worldwide are taking note.

If you have the ability to go vertical you should, and if not make sure you are growing with a high-powered LED fixture to maximize your production.

Re-hunting Your Genetics

The most important step in my opinion when switching from HID to LED is re-hunting your genetics. If you ‘pheno hunted’ your genetics under HID lighting you selected varieties that grow well under that spectrum and environment. As the growing conditions are now slightly different under LED grow lights and the spectrum has changed, so will the expression of your cultivars’ characteristics. Whether it's the plant morphology while growing or the final product there will be differences, some indistinguishable, and some more pronounced.

(Read also: Understanding Different Cannabis Phenotypes)

In Closing

If you have a dialed in HID system that has taken years to perfect you may be hesitant to make the switch to LED fixtures. Yes they are different, but if you’ve dialed in another system you will be able to do the same thing with LEDs, and after a few runs you should start to understand why the majority of cultivators are making the switch as well.

Fohse logoSince 2015, Fohse has been pushing the threshold of what indoor cultivators have dreamed is possible when it comes to yields and quality. Fohse's remarkable, custom made-to-order grow light technologies consistently outgrow every other fixture on the market, and the word is spreading like wildfire. With fixture models for single-level environments, multi-tiered environments, and greenhouses, Fohse serves clients from all corners of the industry. To learn more, visit


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Written by Mike Howard | Director of Cultivation Relations at FOHSE

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Mike Howard is the Director of Cultivation Relations at FOHSE and the former Director of Cultivation at The Grove in Nevada.

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