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The Problem with Bar LED Grow Lights – 4 Ways to Fix It

The Problem with Bar LED Grow Lights – 4 Ways to Fix It

Bar LED grow lights are extremely popular. It’s no wonder – all plants are directly under a light source. This means:

  • There are no hot or cold spots
  • You get an even canopy, with no taller central plants casting shadows
  • All light is beamed down, rather than out - you lose less light to walls

The only problem with using bar LED grow lights in grow tents is that they take up the entire footprint of the tent.

The light fixtures are so large, that once you position them beneath your fan and filter, you’re 30cm closer to your plants. In a standard 2m tall tent, this is insane! With the amount of light modern fixtures emit, you risk getting too close to your canopy.

The latest fixtures have amazing PAR ratings of up to 2.7 μmol/W. At these levels, with reduced headroom, your plants can actually be getting too much light. This leads to growth issues and possible bleaching out of the leaf pigments.

The good news is there are 4 simple steps you can take to avoid this problem.

The solution

There are 4 main ways to deal with this issue and give you back that precious headroom:

1. Dim your Bar LED Grow Lights

Dim your Bar LEDsDim your Bar LEDs

For young plants, this is essential anyway. But in a limited headroom situation it also lets you reduce light levels slightly.

This isn’t ideal though – it’s like buying a race car and then driving it at 30mph – you’re just not getting the most out of your cutting edge grow light.

Many of the best LED fixtures have a dimming function via either a dimming dial on the fixture itself or via an external lighting controller.

2. Upgrade your tent to a taller model

Increase  your tent sizeIncrease  your tent size

You can easily regain height, by upgrading your tent to one that's at least 2.2m tall. There are a number of high ceiling tents available, such as the HOMEbox Ambient 2.2m or Budbox HC models. You get 20cm more headroom than you’d get with a standard 2m tall model.

3. Take your fan and filter out of the way 

Inline extraction KitInline extraction Kit

The new CarboAir Inline Carbon Filters mean that you don’t actually have to have your fan and filter inside your tent anymore! Simply position your fan and filter outside your tent. You get the same amount of extraction and smell filtration, but the clever inline design lets you get back that crucial space at the top of your tent.

4. Add CO2

Add CO2Add CO2

If your bar LED grow light is too close to your canopy, you risk plants getting too much light. You can offset this by adding CO2.

Remember, for photosynthesis (sugar production) to occur, you need light + CO2 + water. If plants get too much light but not enough CO2, photosynthesis is reduced and plants become stressed. With the kind of light you get from top bar LEDs (up to 2.7 μmol/w), make sure you add enough CO2 for optimum photosynthesis. As well as preventing problems, adding CO2 with bar LEDs can increase yields by 20 – 30%. 

How To

Dimming your Bar LED

As with most advanced HPS fixtures, LED dimming is carried out through a 0-10v signal. Depending on which LED you buy, you will have a couple of options.

Exolux Pro Sirius 630w LED

Exolux Pro Sirius LEDExolux Pro Sirius LED

The Exolux Pro Sirius has an onboard dimming switch. This allows you to easily switch between 250W, 380W, 500W and 630W settings.

It also has an RJ45 input for a 0-10v controller and works beautifully with both the Parlux Master Controller and the DLI DLM-4 Zone Controller to automatically dim your light based on temperature, or manually dim as required.

Gavita 1700e LED

Gavita 1700e LEDGavita 1700e LED

This top of the range fixture has some of the highest build quality and best performing components on the market.

The Gavita 1700e LED does not have an onboard dimming switch, so to dim yours, you have two options:

  1. Connect it to a Gavita Master Controller using a special adapter (1 per LED)
    With the EL2 model, you can also control up to 2 other items (e.g. heaters, CO2 equipment). Get an ELF model and you can control fans too.
  2. Use a Gavita RS1 Remote Switch using a special adapter (1 per LED)
    Manually dim or boost lights from 60 – 115% using a Gavita RS1 Remote Switch.

Gavita LEDs won’t work with other brand controllers due to the connection type.

Maxibright Daylight PRO 660w


This second generation of the ever-reliable 600W Maxibright Daylight LED has both increased light output and added external controller ports. There’s an onboard dimming switch that allows you to choose between a 25%, 50%, 75% and 100% output and we look forward to introducing external controllers as soon as they’re available.

Raise the Roof – BudBox High Ceiling & Homebox Tents

BudBox or HOMEBox TentsBudBox or HOMEBox Tents

BudBox Pro Grow Tents are a massive favourite at GroWell. We’ve sold BudBox for over 15 years, and their quality and attention to detail still makes them the best tents money can buy.

HOMEbox tents are another great option. They’re super sturdy with a white interior, which will really help maximise light from your LED.

With either tent, you get a precious extra 20cm of headroom to play with - perfect for bar LEDs. Virtually every bar LED on the market covers a 1.2m x 1.2m (up to 1.5m x 1.5m) area, so look for tents with these dimensions. 

Get Inline – Reclaim your space

Inline extraction KitInline extraction Kit

CarboAir Inline Carbon Filters are a must for the bar LED growers.

They keep your carbon filter fully enclosed in an airtight housing. This means that you can actually take the filter out of the tent. You gain back up to 30cm of headroom and you can mount your bar LED right at the top of your tent.

CarboAir Inline Carbon Filters match the airflow of RVK fans perfectly, so its an easy upgrade if you already have extraction. Alternatively, we’ve put together some great kits including these filters to take all of the hassle out of buying.

Add CO2  - Offset the extra light

CO2 BagCO2 Bag

In small rooms, ExHale CO2 Bags and TNB The Enhancer CO2 Dispersal Canisters do the trick. They slowly release CO2 over a set period of time. All you do is activate them and hang them. It doesn’t get quicker and easier than this.

To cover a larger area, or for tighter control of your CO2 levels, you’re best off using propane gas or bottled gas. Your room is dosed with CO2 when it’s needed, to keep levels at the optimum 1200ppm.


LEDs produce heat that rises up (convection) rather than down over plants (radiant). So during the colder months, you need to add more heat than you would with an HPS. The KlimaHeat Grow Room Heater is great.

About the author

Alex is one of our Directors! It's his job to sniff out the best products and keep operations in order. His toe stays firmly dipped in marketing, too!

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