G.A.S. Day & Night Humidity Controller — Light-Sensing Humidifier Automation
Best for: Growers who need to dial in separate humidity levels for lights-on and lights-off, without the complexity or cost of smart controllers
Our thoughts
Dead simple, genuinely useful, and won't break the bank. If you're running a humidifier and want it to do different things during day and night phases, this does the job without any faffing about with apps or batteries. One we sell a lot of for growers at the early stages of their setup.
The G.A.S. Day & Night Humidity Controller is a light-sensing humidifier controller that automates moisture levels based on your grow lights. It uses a built-in photocell sensor to detect when your lights are on or off, then switches between two separate humidity settings you've dialled in — one for day, one for night. No WiFi. No apps. No faffing. Just straightforward humidifier automation that actually works.
Why day and night humidity control matters
Humidity doesn't stay static through a light cycle. During lights-off, your plants are still transpiring, temperatures drop, and relative humidity naturally climbs. Without separate night-time control, humidity can spike and create the perfect conditions for mould and mildew — especially during propagation or in sealed spaces.
A controller handles this for you automatically. Instead of manually turning a humidifier on and off every 12 hours (or worse, leaving it running all night and risking problems), you set your targets and walk away. Lower anxiety. Better results. Less babysitting.
How it works
Light sensing
The integrated photocell probe sits in a well-lit area of your grow room and detects whether your lights are on or off. It switches between your day and night settings in real time.
Dual dials
Left dial = daytime humidity target. Right dial = night-time humidity target. Both adjustable across the full range. Set once, forget it.
Visual feedback
A green LED lights up when the humidifier is switched on, so you can see at a glance whether it's working. A rapidly flashing LED indicates a sensor issue (replacement sensors are available if needed).
Compatible with your existing humidifier
You plug your humidifier into the controller. The controller switches it on and off based on humidity levels and light cycles. That's it.
How it compares
This sits in the entry-level automation bracket of humidity controllers.
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vs. manual control: You're no longer adjusting settings twice daily. Frees up your time, removes human error.
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vs. smart controllers (WiFi/app-based): You lose remote monitoring and fancy integrations, but gain simplicity, reliability, and a much lower price. No batteries. No software updates. No cloud dependency.
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vs. basic on/off timers: Unlike a simple timer, this actually responds to humidity levels AND light cycles simultaneously. Much smarter than just guessing timings.
In plain terms: if you want day/night humidity control without paying for features you won't use, this is the move.
Usage guidance
Early-stage propagation (seedlings, cuttings)
Set daytime to 70-75% humidity, night-time to 65-70%. Young plants need higher moisture levels and this controller will maintain them without you having to constantly fiddle with the humidifier.
Vegetative growth
Dial in 50-60% day, 45-55% night. As plants mature, humidity demand drops — the controller handles the switch automatically when your lights turn off.
Late flowering
Run 40-50% day, 35-45% night. Lower humidity reduces disease risk. Again, no manual adjustment needed — just set it once and it works.
Probe placement
Position the sensor probe in a well-lit area of your grow room, ideally somewhere that gets full light exposure when your lights are on. Poor placement = poor readings. Avoid shadows, blocked areas, or anywhere tucked away.
Technical specifications
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Manufacturer: G.A.S. (Global Air Supplies)
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Control type: Day & Night Humidity Controller (humidifier version)
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Sensor: Light-sensitive photocell probe (integrated)
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Operating mode: Dual independent dials — left for daytime, right for night-time humidity targets
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Humidity adjustment: Adjustable range across both day and night settings (full range)
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Functionality: Humidification control only — this version adds moisture. A separate dehumidifier controller is available if you need to remove humidity.
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Output indicator: Green LED (lights when humidifier is active; rapid flashing indicates sensor fault)
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Device compatibility: Works with any standard humidifier
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Power requirement: Standard mains plug
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Replacement parts: Sensor probes available separately if needed
Who this is for
- Growers running propagation or cloning setups who need stable high humidity without constant manual adjustment
- Budget-conscious growers wanting to automate humidification without smart-controller pricing
- Anyone preferring simple analog control over WiFi apps and cloud dependency
- Growers in their first or second year who want reliability without complexity
- Small-to-medium grow spaces where a single humidifier covers the area
- Anyone already running a humidifier who wants to make it smarter without replacing it
Best suited to setups where straightforward automation and proven reliability matter more than app integration and advanced features.
Our take
This is proper kit at a sensible price. Day and night humidity control is genuinely useful — it prevents the mould risk that comes with lights-off humidity spikes, and it saves you from babysitting a humidifier manually. The photocell sensor works reliably, the dials are straightforward, and there's no dependence on batteries or software.
If you're setting up propagation, early-stage growing, or just want to automate a humidifier without overcomplicating things, this is worth picking up while stock lasts. Does exactly what it should, day in, day out.
