Humidity Meter aka Hygrometer - Analog vs Digital and How To Use Them - Red Eyes Online

Humidity Meter aka Hygrometer – Analog vs Digital and How To Use Them

 Hygrometers - analog and digital

Indoor growing is a science – you can’t just give your cannabis plants some water and led grow lighting and expect them to grow.

Light, water, and soil nutrients need to be carefully monitored to ensure the best results. Another factor you shouldn’t neglect in your grow tents is humidity.

Too much humidity can lead to mold growth and bud rot, rendering your cannabis completely unusable.

But when humidity levels are too low when your plants are young, they may not receive enough moisture to grow at all. Balance is the key.

What is a Hygrometer?

A hygrometer is an instrument that measures the amount of water vapor in a given space, better known as humidity.

The higher the humidity, the warmer and wetter it feels – the lower the humidity, the colder and drier it feels.

Two rooms at the exact same temperature can feel completely different if their humidity levels are different.

Humidity affects how much moisture your plants receive and absorb, which is why hygrometers and grow tents go hand in hand.

Seedlings and plants in the early stages of growth prefer higher levels of humidity compared to mature plants.

How to Read a Humidity Meter

A hygrometer measures both the temperature and the amount of water vapor in a room to calculate relative humidity, which appears as a percentage.

How to Read a Humidity Meter

So if your hygrometer reads 30%, that means that there is 30% of the maximum amount of water vapor that can be present at that temperature.

The higher the temperature, the greater the maximum humidity. The lower the percentage, the lower the relative humidity – the higher the percentage, the higher the relative humidity.

Once you’ve calculated the humidity of the room your grow box is in, you can use a humidifier or a dehumidifier to adjust accordingly.

Cannabis plants prefer high humidity (70%) as seedlings and lower humidity (40%) as they began to sprout, grow, and flower.

The humidity for flowering plants should be below 40% to prevent mold growth.

Types of Hygrometers

There are two main types of hygrometers – mechanical and digital. Both have their own advantages and disadvantages, but digital hygrometers are more commonly used for indoor growing.

Mechanical Hygrometers

Mechanical hygrometers display relative humidity on a gauge. While usually more aesthetically pleasing, they’re generally less accurate and more difficult to read than digital hygrometers.

The only real advantage mechanical hygrometers have over their digital counterparts is that they don’t require batteries.


A psychrometer is a type of mechanical hygrometer that uses two thermometers, one dry bulb and one wet bulb, to measure humidity.

The dry bulb measures the temperature of the air while the wet bulb measures liquid temperature.

By comparing these two readings, a psychrometer is able to calculate and display the room’s relative humidity.

A psychrometer reading is far more accurate than a standard household mechanical hygrometer reading.

Digital Hygrometer

Easy to read, highly accurate and relatively inexpensive, digital hygrometers are the most popular way to measure relative humidity.

Digital Hygrometer

They’re able to record and keep track of fluctuations in humidity so that you can see if there were any major changes while you were out of the house.

Many come with additional bells and whistles such as an alarm system, clock, and backlighting.

Photos from: amphoto /, nuttawutnuy /, VIPDesignUSA /

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