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Light Leaks: Why do they Matter?

Light Leaks: Why do they Matter?

You don’t need us to tell you how important your light cycle is.

Your light cycle affects the way plants grow. It signals to plants to start fruiting or flowering. It also has a big impact on your growing environment.  

Any exposure to natural light during ‘lights off’ can be a disruption.  At best, plants will become stressed and your yield will be dented. At worst, you can get genetic abnormalities.

This is an even bigger problem if you run your lights at night. It works both ways - natural daylight can seep into your tent during ‘lights off’…OR…grow light can leak out and disturb neighbours at night.

Why Light Leaks Matter

If you have a light leak, here's what can happen.

1. You will disrupt the ‘lights on/off’ cycle

Lights on and offLights on and off

Plants perform different key functions at night than they do during the day. Light coming in during the dark period can disrupt key functions.

One example is the way plants use CO2. When lights are on, plants absorb CO2. When lights are off, plants release oxygen. That’s why we only recommend dosing with CO2 during the day.

What’s more, the switch from an 18hr veg cycle to a 12 hr flowering cycle signals to plants to switch to flowering.  Any light leaks after the switch can disrupt this and put plants back into vegetative growth. You may even get genetic abnormalities in some species of plants.

2. Plants get stressed

Plants stressedPlants stressed

Plants perform best in a stable climate. Any inconsistencies can cause stress. When stressed, plants don’t perform key functions as well (e.g. photosynthesis, nutrient absorption).

3. It’s not just light leaking in and out


A sealed environment isn’t just about your light. You want to keep pests out and CO2 in. You don’t want any air escaping before it’s gone through a carbon filter, either.

If there’s a light leak, the chances are other things are sneaking in and out of your tent. You haven’t got as much control over your environment. You're also risking a bug breakout – especially in summer!    

4. You can disturb sleeping neighbours

Sleeping neighboursSleeping neighbours

Light leaking out when it’s dark can be a disruption to anyone sleeping in the room your grow tent is in.

How to Stop Light Leaks

The good news is, there are lots of ways to prevent light leaks.

1. Invest in a quality tent

quality tentquality tent

There’s a reason some tents cost more than others.

They have thicker canvases, tighter stitching and quality zips.

We’re a big fan of the BudBox build. They have a very dense weave on their canvas and a thicker reflective coating than most tents we’ve seen. It’s tough for any light to seep in.

Most tents have light baffles on zips - these are bits of fabric that sit behind zips to stop light seeping through cracks in zips.  BudBox tents have light baffles for anything that’s been sewn.

Their green viewing window lets you check on plants without waking plants or even unzipping your tent.

Make sure that you pick a tent with drawstring ports – you tighten them around ducting to keep light out.

2. Cover any windows or doors with reflective sheeting

reflex sheetingreflex sheeting

Curtains won’t cut it – light can still enter the room your tent is in.

To keep natural light out and grow light in, cover any windows with reflective sheeting.

Reflex Total Blackout is ideal. It is 3 layers thick.

This keeps natural light out of the room your tent is in. It also stops grow light disturbing neighbours at night.

3. Check on plants during ‘lights off’, using a green light

Green lightGreen light

If you run lights at night, don’t switch any lights on if the light might reach plants. Instead, use a Green Light Head Lamp. It has a neutral, green light that matches the pigmentation of plant leaves.

Plants are unable to detect or absorb green light, so it has no impact on plants.

4. Check for light leaks

Light LeaksLight Leaks

Some light leaks are so small you might not even notice they’re there. Always be on the lookout.

Make sure you check zips, corners and joins. Zip yourself into your tent. It should be pitch black and any light leaks on your canvas will show up as tiny spots of light.

You can patch up any cracks with duct tape.

Ideally, you’ll want to check at different times of day, when sunlight will hit your tent from different angles.

5. Be ready to repair

Hook and LoopHook and Loop

If you’re heavy handed, zips might break and canvasses might tear. Make sure you’ve got some hook & loop tape handy to replace broken zips. You can fix torn canvas using duct tape.  

6. Cover the lights on your equipment

Gaffa TapeGaffa Tape

Lots of bits of equipment have lights on them to show they’re on and working. Some also have warning lights. You need to cover these up. A little bit of duct tape should do the trick.

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About the author

Ian's our Sheffield shop manager. He loves tinkering in the greenhouse. Drop by to see what he's growing.

GroWell Hydroponics Sheffield

Call GroWell Sheffield:
0114 243 9242

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