Did you know that you can get more out of your grow lights by measuring the light levels with a lux meter? Lux meters help growers optimize their light conditions to produce healthier plants.

Indoor cannabis growers often lack sun exposure, so how can you measure the amount of light your plants are receiving?

The answer is a lux meter, which measures brightness! A lux meter is used to measure brightness. The term “lumen” refers to the amount of light being received at any given location. Lumens are a unit for measuring illumination. So, in other words, a lux meter can tell you how much light reaches any specific point in your grow area.

What Is a Lux Meter?

Previously, we briefly mentioned what lux is (lumens per square metre) and how it measures the intensity of light. In regards to growing cannabis, a lux meter helps growers determine the intense level of light hitting their plants about how far away the plant is from the original light source.This may provide you with a hint as to whether the amount of visible light your plants are receiving is uniform. In other words, it can help you determine if some plants, or particular locations of plants, are losing out on light, or getting too much.

What Is the Difference Between Lux and PAR Meters?

Lux meters, as you may recall, only indicate light intensity. Luxometers, on the other hand, fail to account for important details. PAR meters are a good example of this. lux measures the amount of light that humans perceive (lumens), but plants also absorb light outside of this range. Not only that, but because lux values yellow light above all else, cannabis plants don’t utilize it for photosynthesis.

Although sensors for measuring PAR (photosynthetically active radiation) meters measure the amount of light cannabis plants can actually use for photosynthesis, including infrared and ultraviolet wavelengths.

So, if that’s the case, why wouldn’t you just purchase a PAR meter for yourself and avoid lux altogether? It’s a straightforward issue of dollars. While a simple light meter may be purchased for under $25, PAR meters can cost anywhere from hundreds to thousands of dollars.

Although lux meters have their uses, they don’t show the complete amount of light that your grow room or cannabis plant is receiving.

How Does a Lux Meter Work?

Lux meters aren’t difficult to use, and all you need is an understanding of what you’re looking for. growers can utilize a lux meter by measuring the light intensity within a waveband from 380-700nm. A semiconductor known as a photodiode then transforms the light into an electrical current, allowing growers to estimate if their plants are receiving enough light (which will be elaborated on shortly).

What Are the Benefits of a Lux Meter?

First and foremost, having a lux meter is handy. They’re inexpensive to source and super easy to use. By allowing you to get a read on the luminous flux in your grow room, you can maximise light exposure for optimal development (i.e. big yields from healthy plants).

A lux meter can also help you if your plants are getting too much light or if they’re too close/far from the light source. By doing this, you can avoid any problems with bleaching, stretching, nutrients, and more.

Lux meters can also be useful in determining whether a specific lamp’s power is failing or deteriorating with time—don’t overlook how useful this tool is. Lux meters may be quite eye-opening, revealing which parts of your grow room get the most or least light. From here, you may use them to plan your layout or rearrange your grow room to ensure that you don’t squander any resources.

Lux meter benefits:

Inexpensive
Helps you maximise light exposure for bigger yields
Helps you minimise stress on plants
Helps you indicate the power of certain types of grow lights
Tells you where light is most/least intense in grow room

How does a lux meter help you?

Bigger Yields – Plants that get the appropriate amount of light grow faster and have larger yields. The “sweet spot” for your grow light, where your plants receive the most light without burning, is determined by a lux meter. It also aids in spacing out your plants and experimenting with various lighting setups to maximize yield in the sweet spot.
Test Your Bulbs – You may use a lux meter to discover when new bulbs are required. Most grow lights with replaceable bulbs get weaker with time, and they must be changed after several harvests (depending on the case, for example, LEDs can last for years). A lux meter can help you determine exactly when it’s time to change your bulbs.
Healthier Growth – You may check on certain aspects of the plant to see whether they are receiving too much or insufficient light. Lux meters can also assist you avoid light damage caused by excessively high lux levels.
Better Than Your Eyes – We often can’t tell by looking which areas of a room are getting the most light. To ensure we’re making the best use of our space and light, it’s helpful to invest in a lux meter. Sometimes simply moving a plant or adjusting a grow light by inches can dramatically alter how much light your plants get – and thus their growth.

The lux meter was my first introduction to the world of light meters. For this crop, I’m using a 250W HPS for the first time. I wasn’t sure how far away from my plants I should keep the lights. Fortunately, I had a lux meter on hand to provide me precise answers. I began measuring light levels and how they differ with plant position and location.

After some trial and error, I discovered that the optimal distance to keep my 250W light from these plants was 11-12″.

I constantly monitored the lux levels throughout their life!

As my plants grew, I made a point to ensure they were all getting an equal amount of light. Once my plants hit the flowering stage and started developing buds, however,

I realized that I could optimize bud growth by moving everything 3 inches to the right– Crazy, right? Without any prior knowledge on plant shadows and how they fall under lights based on shape and cola position, there’s no way I would have come to this conclusion simply from looking at my plants.

Here’s a quick video explanation:

A lux meter helped me achieve bigger harvests by allowing me to distribute more light to my plants. The nicest thing is that I didn’t need to replace my grow lights; rather, I was able to get higher efficiency out of the same lights simply by changing their positions.

Using a Lux Meter for Different Types of Grow Lights

As the name suggests, a lux meter measures lux. For those unfamiliar, lux is a measurement of the luminous flux in an area. To put it simply, it tracks how much light is visible to human eyesight. Though, some grow lights produce light in infrared and ultraviolet waves- where humans can’t see them. Because of this, The reading from a lux meter would be lower than what’s being produced by the plant if that invisible light was taken into account.

A lux meter is unable to quantify PAR (Photosynthetically Active Radiation), which is a term you’ll come across often when discussing grow lights. Because PAR reflects light that may be utilized for plant photosynthesis, it’s measured inPAR, whereas lux measures visible light for humans.

So basically, lux meters aren’t very useful for grow lights? Nope!

Although it might not seem like it, the range of light used by plants and what humans can see is actually quite similar. While you could buy more precise equipment to measure light levels inPAR, a lux meter will suffice for growers who are doing this as a hobby. Just remember that your measurements aren’t exact so leave some room for error.

Note: There are more expensive light meters on the market that are better at comparing light levels across different types of grow lights, but our lux meter is a decent place to start. We haven’t needed to upgrade to a higher model because we haven’t had the need. If your grow light produces a lot of Infrared or especially UV light (like LEC grow lights and some LEDs), your plants will be getting way too much light than what’s measured by a lux meter.

The visible wavelengths of light are shown in the chart below. This is also a curve that depicts what type of illumination a lux meter detects.

How much lux do you want to deliver to your plants?

This is a brief summary. A lux meter, as previously said, only provides a rough approximation. Here’s our comprehensive guide on how far away to keep grow lights from plants.

Quick Guide – Lux Levels for Optimal Cannabis Growth

< 15,000 lux – sparse or “stretchy” growth – plant isn’t getting enough light

15,000 – 50,000 lux – a good amount of light for healthy vegetative growth

45,000 – 70,000 lux – the proper amount of light for cannabis plants in the flowering (budding) stage is at a wavelength of 5,000 to 8,000 nanometers. If grow lights give off a lot of UV light (such as LEC), keep them around the lower end of this range.

70,000 – 85,000 lux – brightly-lit conditions, some strains of plants do very well, but others (particularly Indica strains and auto-flowering varieties) lose their top leaves quickly. In these circumstances, lights need to be kept further away from the plants for healthy growth.

> 85,000 lux – at this light intensity, you’ve exceeded the plant’s “saturation point,” which indicates that your plant can’t utilize all of the light (most strains will show light bleaching or other serious indications of stress at this level!)

What Happens If I Give My Plants Too Much Light?

The light you receive from the sun on a sunny day is approximately 40,000 to 100,000 lux. On the upper end, the sun gives off more light than what the plant can use. For example, if there was a cannabis plant in a pot located in the dessert under direct sunlight; it would be too much for the plant.

You don’t get any more growth from increasing the amount of light to reach 85,000 lux while growing cannabis. Not only is it extra light wasted by your plants, but too much illumination can also cause your plants to suffer from light burn or prematurely lose their leaves!

I highly suggest obtaining a lux meter, especially if you aren’t as familiar with the grow lights you’re utilizing. You may compete with cannabis growers who use bigger light fixtures with a lux meter!