Does a grow light produce heat? Yes. Here’s why that matters and how to manage it.

I’ve worked with commercial lighting systems for 8+ years. I’ve personally made—and documented—about 14 significant heat-management mistakes, totaling roughly $12,000 in wasted electricity and damaged crops. Now I maintain our facility’s thermal checklist to prevent others from repeating my errors.

One of the most frequent questions I get from growers switching to LED is: does a grow light produce heat?

The short answer is yes. All grow lights produce heat. But the kind of heat, where it goes, and what you need to do about it is completely different between LED (like a Fluence SPYDR or VYPR) and traditional HID (like a 1000w double-ended).

This isn't theoretical. I spent my first year assuming LEDs were 'cool lights.' That assumption cost me a $3,200 batch of basil in September 2022. Let me rephrase that: I ruined a crop because I confused 'efficient' with 'cold.' They are not the same thing.

Here is a 5-step checklist to understand and manage grow light heat. Follow this in the order presented, and you will avoid the mistakes I made.

Step 1: Identify the type of heat your fixture outputs

This is where most people get it wrong. We didn't have a formal training process for this when I started; cost us when we installed our first batch of LEDs.

A 1000w HPS lamp converts roughly 60-70% of its energy into radiant heat. That’s the infrared energy you feel on your face. You need high air exchange rates to pull that heat out.

A 600w Fluence VYPR, on the other hand, converts only about 30-40% of its energy into heat. But that heat is mostly conductive (the fixture body is warm) and convective (the air around the fixture is warm). The radiant heat hitting your plant canopy is significantly less.

Is one better? Yes. With LEDs, you are heating the air, not the leaf. In a sealed greenhouse with CO2 enrichment, this is a massive advantage. But if you simply swapped a 1000w HID for a 600w LED without checking your HVAC, the leaf temperature drops too low. You overwater. You get edema. The growth slows down.

That’s exactly what happened to me in 2022. I saw the power savings and ignored the physics.

Step 2: Measure leaf temperature—not ambient room temp

In my opinion, this is the single most important metric you are probably ignoring. Does a grow light produce heat on the leaf? Yes, but less than HID.

We use an infrared thermometer gun. For a HID setup, you might want leaf temps of 75-80°F (24-27°C). For a FLUENCE LED setup, you generally want leaf temps of 78-84°F (26-29°C). The air temperature is a lie. The leaf temperature is the truth.

Personally, I check leaf temperature an hour after lights-on and an hour before lights-off. Put another way: if you only check at noon, you are missing the temperature dip at sunrise.

If your leaf temp is too low (say 72°F under LEDs), the plant’s metabolism slows down. You get condensation on the leaf surface. That’s a recipe for botrytis. So you might need to increase your ambient air temp by 2-3°F compared to your HID schedule. That feels wrong, but I’ve verified it through three crop cycles.

Step 3: Separate your 'air cooling' from your 'fixture cooling'

This is a step in our internal checklist that we only added after a 'heat build-up' disaster in Q1 2024. We had a rack of SPYDRs running 18 hours/day. The room temp was perfect (75°F). But the fixtures got very hot to the touch. Like, burn-your-hand hot.

I called Fluence support. They politely explained that the VYPR and SPYDR fixtures are actively cooled (internal fans). The heat needs to be pushed out of the room, not just blown around. We had a circulation fan blowing directly on the fixtures. That just pushed hot air down into the canopy.

We installed dedicated exhaust ducts directly above the driver banks. Did it fix the crop stress? Yes. Did it cost me $800 in ducting and labor? Yes. Was it worth it? Absolutely. The third time we had heat stress on the top leaves, I created a 'fixture exhaust' verification step in our pre-season checklist.

Action item: Touch the driver of your Fluence LED. If you cannot hold your hand on it for 10 seconds, that heat is staying in your grow space. You need to mechanically remove it.

Step 4: Account for 'reflective heat' with your trellis and walls

I should add that this step is often overlooked in blogs titled 'Does a grow light produce heat?' because they only talk about the bulb. But in a commercial setting, the materials matter.

A white poly wall reflects light. It also reflects radiant heat. In a 10,000 sqft room with Fluence fixtures, if all your walls are white Tyvek, the reflected infrared is not zero. It's low (maybe 10-15% of the original heat load), but it adds up.

In our trial room (July 2024), we measured a 4°F temperature increase at the plant level directly adjacent to a white wall compared to the center of the room. The solution? We hung a 6-foot strip of flat-black shade cloth between the wall and the first row of plants. It absorbed the heat before it hit the plant. That is an easy, $50 fix that many people miss.

Step 5: Match your HVAC sizing to the 'sensible heat ratio' (SHR)

Alright, this is a bit technical, but it's the final puzzle piece. HVAC contractors usually size AC units based on 'total heat load' (BTU). But LEDs are different from HIDs because they have a higher sensible heat ratio.

Sensible heat is heat you can measure with a thermometer (air temperature). Latent heat is moisture (humidity). HID lamps push a lot of infrared (radiant heat) which directly evaporates water (latent heat). LEDs push more sensible heat (air temperature).

Per industry data (Source: American Society of Agricultural and Biological Engineers (ASABE) EP406.5 standard, 2024), LED lighting systems can have an SHR of 0.85-0.90, while HID is closer to 0.70-0.75.

What this means for you: Your standard AC unit designed for HID might not have enough 'latent cooling' capacity for an LED setup. You might end up with high humidity and high temperature, which is a terrible combination. (Prices for dedicated dehumidification units as of January 2025 range from $5,000 to $25,000 depending on size. Verify current pricing at major HVAC suppliers.)

If you are converting a room from HID to Fluence LED, get an ASHRAE engineer to re-calc your SHR. Ignore this, and you'll be adding a dehumidifier later. I wish I had skipped that mistake.

Summary of my mistakes (so you don't make them)

Here is the hard truth from my 8 years of buying and managing large-scale lighting:

1. LEDs definitely produce heat. They just produce less radiant heat than HIDs.
2. Measure leaf temperature, not room temperature. Your Fluence fixture's efficiency means leaves run 2-4°F cooler. Adjust your thermostat.
3. Actively exhaust fixture heat. If the driver is hot, the air around it is hot. Get it out.
4. Check your reflective surfaces. White walls bounce a bit of heat. Mitigate it with shade cloth.
5. Recalculate your SHR. Your old AC might not handle the new heat profile. A $1,000 engineer consultation can save you $20,000 in dehumidifier costs.

Oh, and one final thing: does a grow light produce heat is the wrong question. The right question is: Where is the heat going, and is my equipment designed to remove it?

Prices as of January 2025; verify current rates for equipment and consulting. Regulatory information regarding ASHRAE standards is for general guidance only; consult your certified engineering firm for current requirements.