How to Use a Lux Meter for Better Cannabis Yields?

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Added 29 September 2022

Your cannabis plant needs a lot of light. 

There’s no dearth of light outdoors, but it can be challenging to provide all the light the plants need indoors. 

As an indoor grower, you need to compensate for the lack of sunlight by adding adequate grow lights in your grow room.

But many new indoor growers make a big mistake — they simply hang whatever lights they find without checking whether it is enough for the plant’s healthy growth and eventual yield. The problem doesn’t end with choosing the light, either. Even if they have the best grow lights, but are not placed properly, the plant’s growth and yield can suffer.

Avoid falling for this trap by choosing the right kind of grow lights for your plant and placing them in an ideal position for the best light exposure. But how do you do that?

Should you just place them after referring to some online charts or follow what other growers on Reddit are doing? Not really. There is a better way to ensure your lights are properly placed, thanks to lux meters.

In this article, learn all about using a lux meter for your cannabis plant so you can improve your plant’s yield. 

What is a Lux Meter?

lux meter

A lux meter is a basic device that measures lux — a unit of the illuminance of light. With a lux meter, you can measure luminous flux per unit area, which refers to the perceived intensity of light in a specific area, most usually a square meter — lumens/meter square.

When you are growing cannabis, a lux meter helps you measure the intensity of your grow lights with respect to their distance to your cannabis plant. So, with a lux meter, you can check if your plant is getting enough light or if the light is fixed at the right distance for the best results. 

A lux meter is a simple device. It uses a semiconductor known as a photodiode, which converts light into an electric current. And it can measure the intensity of light between the wavelengths 380 to 700 nm. 

What makes a lux better even better is that it is easy to understand even for novice growers who don’t know a lot about the intricacies of lights yet. If you know what you want, it is as easy as using a thermometer to check the soil’s temperature. 

For a cannabis grower (or any other grower), a lux meter is a small investment that can take the cultivation far. Sure, they are not the most accurate assessment of light, but they get the work done in a jiffy. More on this later in the article.

What are the Advantages of Using a Lux Meter to Grow Cannabis?

What are the advantages of lux meter

You can grow cannabis just fine without a lux meter, but you should still consider having it in your gardening kit because it can make your plant’s life easier and better and give you better yields than before. Here are some reasons why every cannabis grower should have a lux meter.

  • Understand Your Grow Lights Better

When you use grow lights for cannabis, they need to be positioned well and have an adequate light intensity to sustain your plant. If the grow lights are too dim, your plants can grow slowly and produce larfs (low-quality buds) because they will fail to produce enough energy. 

On the other hand, if the lights are too bright or too close, your plant can experience bleaching or light burns. In some cases, the plant may also dry out. And let’s not overlook the monetary aspect of using lights that are too bright — wastage of electricity, which can get quite expensive in the long run and is also bad for the environment.

But you don’t just have to rely on the light wattage since it is not an accurate insight about the light’s intensity, especially if you are looking at an LED light. Wattage used to be the industry standard for light measurement because everyone used HID lights back then, but now, things have changed with LED lights, which are more efficient at producing light.

A 150W LED does not produce the same amount of light as a 150W HID or CFL light.

This is why you need a reliable device that can do the hard work for you and give you an idea of how well your lights are working instead of relying on the light’s packaging. With a lux meter, you can see exactly how much light intensity is produced by the source, regardless of the wattage.

  • Prevent Common Plant Problems

Once you know your lights better, you can also prevent so many common problems that cannabis plants face due to improper lighting setup. With a lux meter, you can prevent common problems like light bleach, light deficiency, heat burns, etc., leading to a healthier plant with a vibrant, bushy canopy and buds. 

By ensuring your lights are adequate for your plant, you don’t have to worry about such problems, let alone even trying to fix them.

  • Plan Your Garden Better

Light acts as a wavelength, so if you are using a single light source, it will be more intense at the center of the light fall and fade off around the edges. With a lux meter, it becomes easier to measure light fall in your garden, so you can place your plants where the light intensity is ideal or add more lights to fill in the dark spots.

  • Know When to Change Your Lights

Some types of grow lights, like HPS or MH lights, degrade over time and experience a performance drop. Over time, these lights become dimmer and produce low light intensity, which can hinder your plant’s growth drastically. 

But this degradation is hard to notice by the human eye until it is too late. Our eyes get used to the light, so it can be hard to notice minor changes over time. We fail to notice such degradations when it occurs over weeks. 

In this case, you can use a lux meter to measure light intensity regularly. If the readings go below your liking, it’s a sign that you need to replace your lights. 

What is the Optimal Light for Cannabis?

What is the Optimal Light for Cannabis?

Cannabis plants need light, but not always of the same quality. The two most important aspects of light for cannabis are intensity and color temperature. Light intensity is how strong light is and color temperature is the spectrum of light.

When cannabis is growing, it needs different levels of light intensity and color temperature, depending on the plant’s growth stage. 

For example, if the light is too dim for a seedling, it will grow weak and leggy, but light too strong will cause light burns, which the seedling won’t be able to handle. When the plant enters the vegetative stage, it needs more light because it is growing bigger with wider fan leaves. And when the plant blooms, light is crucial for bud development and so the demand increases further. 

Ideal Light Intensity for Cannabis Plants

Here are the rough lux ranges your cannabis plant needs to grow well in each of its growth stages:

  • Seedling stage: 5000 to 7000 lux
  • Vegetative stage: 15,000 to 50,000 lux
  • Flowering stage: 45,000 to 65,000 lux

Remember, these are rough figures and your plant’s light requirements may vary, depending on the strain and other environmental factors. Ideally, you should limit the light intensity to 65,000 lux for flowering plants even though plants can handle light up to 75,000 lux.

You should also understand your strain better. Some strains don’t require a lot of light and will do just fine on the lower end of the above-mentioned ranges, but some strains may require the most light within the recommended range. Always purchase seeds from reputable dealers who give you exactly what you order and are transparent about their strain’s characteristics. 

Also, do not fall into the “more light, more growth” trap. This only works until the 75,000 lux mark. If the light is more intense than this mark, expect your plant to show signs of stress, like light burns or bleaching, dry leaves, or small buds. 

Ideal Color Temperature for Cannabis Plants

As mentioned earlier, cannabis also requires a different type of light at each of its growth stages. The sunlight is never the same — its color temperature changes with the seasons. So, you need to bring the same element to your indoor garden so that your plant can grow just as well as an outdoor plant. 

But why is a different type of light important? This is because specific light spectrums affect the plant in different ways, leading to better growth and bud development. 

When the cannabis plant is in its vegetative stage, it prefers a blue-dominant light spectrum between the waveband of 400 to 500 nm, since this color aids in the plant’s mass growth. On the other hand, a flowering cannabis plant prefers red-dominant light between the waveband of 620 to 780 nm, where the red light enhances bud development.

Luckily, some lux meters can also measure the color temperature and help you figure out exactly what kind of light is falling on your cannabis plant. This way, you can fine tune the light spectrum to aid your plant’s growth and promote better bud development.

How to Use a Lux Meter for Best Cannabis Yields?

How to Use a Lux Meter?

Now that you are convinced to use a lux meter, the next step is to learn how to use it. Using a lux meter for growing cannabis is all about finding the sweet spot between your plant and the light source. 

Steps to Use a Lux Meter

And the ideal distance may differ depending on your strain and the type of light you use. Based on the recommended ranges above and your plant’s strain, figure out how far you would need to place your lights. This is not permanent, just a starting point. If you are still not sure, place the lights roughly 150 cm from the floor. 

Once you have set up the grow lights, it’s time to crank up your lux meter. Follow these steps on using a lux meter to grow cannabis.

  • Take Readings Across the Growing Space

Turn your grow lights on and start measuring the light across the growing space. And while doing so, hold your lux meter directly under the light and then move around the space to spot any dark spots.

  • Place Your Plants

Once you have taken the readings, use them to place your plant where the light fall is strongest. Usually, it will be right under the grow light. However, if you are growing multiple plants, you need to arrange the plants so that each of them gets equal and adequate light. 

Light falls off on the sides and with distance, so you may need to adjust the light source or add more lights, depending on the space, type of light, and the number of plants you are growing.

  • Optional: Set the Color Temperature

If your grow lights’ color temperature can be changed, change it to match your plant’s growth stage. In the veggie stage, maintain the light temperature with blue dominance, and in the flowering stage, set it to be red or orange dominant. 

  • Adjust As Your Plants Grow

Every week, your plant will noticeably grow taller and wider. While growing, if the grow lights are too close already, your plant may experience light burn. And while growing wider, the canopy may grow out of the ideal light range. 

So, it is recommended that you measure the light at least on a weekly basis to ensure your plant is getting adequate light all around, not just in the middle of the canopy. You may have to rearrange your light source, depending on the lux meter readings.

Light Brightness and Distance from Plant

If the lux falling on the canopy is more or less than what your plant prefers, you need to adjust the light. And you can do so in two ways: changing the light’s brightness or moving the lights closer or farther away from the plant. 

Ideally, you should move the light panels first instead of cranking up the brightness as some lights produce more heat the brighter they run. Unless you want to heat up your grow room slightly — in that case, use the dimmer to increase your light’s brightness. 

LED Lights for Cannabis Plants

Many cannabis growers are switching from regular lights to LED lights because it offers a ton of benefits over traditional light sources, such as extreme energy efficiency, reliability of up to 11 years, lower heat emission, and ease of use.

However, some LED lights can cause some problems when you want to measure their lux using a lux meter. This is because lux meters are designed to read all types of white light, except purple. 

If your LED panel emits purple light due to the mixing of red and blue diodes, the lux meter may fail to measure the light quantity properly. Unfortunately, most cheap LED lights to fall in this category. 

The solution to this problem is to rely on manufacturer information regarding how much light the LED panel produces or use a light meter that can read purple light, which may be a bit expensive. 

Lux Meter Apps: Are They Any Good?

Lux Meter AppsNowadays, smartphone technology has come too far and one phone can do a lot of things, and this includes measuring the light intensity. And there are many apps on both Android and Apple phones that let you measure the light levels. 

So, can lux meter apps replace lux meters? Well, these apps are a good starting point for novice growers as they display the information in a handy format, but they are far inferior to traditional lux meters. Many growers have also experienced that these apps are far from accurate because they use the camera sensor and software, not a photodiode.

So, yes, you can use lux meter apps for starters, but don’t completely rely on them. They are not always accurate.

Is Lux Meter the Best Way to Measure Light?

Is Lux Meter the Best Way to Measure Light?

Lux meters are a solid investment but they are far from the best. Lux meters have some limitations that other light meters don’t.

For example, lux meters are not the most accurate way to measure light. Lux meters are designed to measure light as the human eye perceives it, which is not always what the plant needs. Our eyes are more sensitive to green and yellow spectrums of light, not red and blue. 

While growing cannabis, you need a meter that can measure the photosynthetically active radiation (PAR) light, which is the kind of light that plants use for photosynthesis. The best way to measure light for growing cannabis is using a photosynthetic photon flux density (PPFD) meter, which measures PAR light hitting a square meter in a second. This is measured in μmol/m²/s.

PPFD meters show you how much useful light (for plants) is falling on your cannabis canopy in a second. 

For optimal growth of the cannabis plant, the PPFD readings should be in the range of:

  • Seedling stage: 100 to 300 μmol/m²/s
  • Vegetative stage: 400 to 600 μmol/m²/s
  • Flowering stage: 800 to 1000 μmol/m²/s

But still, for a novice grower, it is advised to use lux meters and not PPFD meters because the former is accessible and affordable. PPFD meters are far more expensive and usually not worth the investment for a home garden unless you are producing a commercial quantity of cannabis.

A lux meter costs around EURO 20, while a PPFD meter costs over EURO 200, and some even go over EURO 2000!

In this case, a lux meter works well enough to give you an idea about your light intensity. It is not the most accurate, but it is better than nothing. And it is a good starting point for cannabis growers, too. 

Summary: How to Use a Lux Meter for Better Cannabis Yields?

Lux meters are basic devices that measure the amount of light falling on a surface. And if you are growing cannabis, you should definitely consider investing in one as it offers various benefits for both you and your plant.

A lux meter helps you understand your grow lights' performance and capabilities, so you can ensure they are right for your plant. Plus, they allow you to fine-tune your grow lights as per your plant’s needs, leading to better health of your plant and avoiding plant problems that occur due to light problems.

Additionally, a lux meter helps you plan your indoor garden’s layout in a better way so that your plants can use the lights more efficiently without a lot of light wastage. 

All of these benefits come together to help improve your plant’s yield when it’s time for harvest. As you know, the more light (to some extent) your plant gets, the better it will grow with big, juicy buds. 

And using a lux meter is easy too. Simply place your grow lights at the recommended height and measure the light quantity with the lux meter. Next, place your plant where the light is strongest and, when your plant grows, keep adjusting your lights to maintain the ideal light levels.

And if you want to be even closer to understanding your lights and are okay with investing a lot of money, upgrade to a PPFD meter. It is far more accurate than a lux meter but considerably more expensive. 

Once you understand your plant’s light requirement and give it the kind of light it needs, your plant will reward you unlike ever before. Light is crucial for your plant, and any light source does not suffice in most cases. 

Don't make the same mistake many new growers make of placing whatever light they have over their cannabis plant and hoping for the best. 

Use a lux meter to get closer to the goal of creating a perfect lighting environment for your cannabis plant. 


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Thanks for this article! I got a very simple lux meter now and I think it is a must have tool for a grower. Very handy at particular moments like general setup and switch of phases.
I don't personally see any difference in yield from different color temperature. Balanced white lite is best . LEDs are all blue spectrum fixed with levels of red / orange filters . Blue / red or blurple lights work ,not as efficient as a modern simple " white light " led. As for light meters . A smart phone has a sensor that is 1/8 inch diameter. And these sensor s do not pick up light from an angle very well. That said any light meter is good . What is most important is measuring the light at canopy level . The tops of the plants should be as even as possible. The light at canopy level should be consistent . I measure in lumens as that's the same spectrum as our eyes see in . Plants use the exact same spectrum. Light Meyers can be purchased for ten $ that measure lumens . Probably as accurate as a phone app. Accuracy is not important . It's far more important to know exactly how the light is reaching the canopy . Single lights cause a hot spot of light . Multiple lights are far more efficient at getting an even distribution of light at the canopy. Bonus of Led is lights probably last 5 years or half of 50, 000 hours which they are all rated for . Hid and HPs should have bulbs replaced each year , 2 years tops . Expensive PAR meters are cool tools to make you look like a pro . Observation is the key to a good crop. Get to know and understand the tool" light meter" you are using .