lumens for cannabis

How To Use A Lux Meter To Increase Your Cannabis Yields

For healthy growth and good yields, almost nothing is more important than providing your cannabis plants with plenty of light. With an affordable lux meter, you can measure and optimise the amount of light in your grow-op to increase your yields.

If you want to max-out your yields, you need to make sure that your cannabis plants are receiving an adequate amount of light. With a lux meter, this all becomes easier than ever!


A lux meter is a relatively simple device with which you can measure the amount of light (lux=lumens/m²) in your grow room. What makes a lux meter attractive compared to a PAR meter or quantum light meters used by professionals is that it is much cheaper. While a good PAR meter can easily cost €1,000 or more, you can obtain a lux meter for a lot less. Simple lux meters start at €20 and upwards.


Helps Increase Yield

A lux meter can help increase the yield of your cannabis plants—an obvious benefit to growers. With it, you can determine the optimal spots within your grow room, or you can use it to determine the proper distance from your lights to your plants. A light meter/lux meter also lets you know when the light you’re using is simply not enough for maxing out yields.

Tells You When You Need To Replace HID Grow Lights

Some types of grow lights, such as MH/HPS bulbs, have a limited lifespan. In due time, they get increasingly dimmer, and this is why they need to be replaced at certain intervals. The light meter can reliably let you know when you need to replace your MH/HPS bulbs.

Prevents Some Plant Problems

Both insufficient light and too much light can be bad for your cannabis plants. The light meter can help you ensure healthy plant growth throughout all stages. The proper amount of light, not too much and not too little, will reduce stress on your plants, preventing further issues like light burn and bleaching.


How much light your plants need will vary based on each phase of the grow cycle. Seedlings can’t take a lot of light, but once a plant is in veg, it needs just about all the light it can get. This allows plants to grow vigorously to their full potential. The same goes for flowering. Although plants in bloom thrive under a different spectrum of light than during veg, they still need a lot of light exposure to make sure the buds are as big as they can be.


  • Clones and seedlings: 5,000–7,000 lux
  • Vegetative growth: 15,000–50,000 lux
  • Flowering: 45,000–65,000 lux
  • Maximum recommended amount of light: 75,000 lux

What about even more light? At some point, increasing the light beyond a threshold plant can manage will actually diminish returns. Said differently, once you reach about 85,000 lux, it’s simply too much. Some strains may already show signs of light stress at only 75,000 lux, with the risk of light bleaching increasing at over 80,000 lux. To keep it safe, it is best to stay at or below 75,000 lux.


When you use a lux meter to measure the amount of light in your grow room, make sure you measure at the height of your plants’ canopy. This allows you to determine how much light they’re actually receiving. Even if the distribution of light across your growing area may appear even, you should take a number of measurements in different spots of the grow room. This is how you can find blind spots or optimal spots that are not always obvious to the unaided eye. When you locate these spots, you can rearrange your plants accordingly for best results.


A lux meter works with all types of “white” lights, which includes HID, CFL, and white LEDs (COB LEDs). However, it doesn’t work with “purple” LED lights, which emit a purple light due to their combination of blue and red LEDs. Unfortunately, most cheaper LED lights are these purple types. So, if you use one of these for growing, you would have to rely on manufacturer information about how much light the product really emits. Alternatively, you could obtain a light meter that can be used with these types of LEDs. But be aware that these often cost a lot more.

With a lux meter, you can measure and optimise the amount of light your cannabis plants receive, which helps to boost final yield.

Wattage and Lumens of Cannabis Grow Lights

Generally speaking, the higher the wattage of the bulb, the more light it produces. The more light that is produced, the better your plants will grow. An excellent way to measure the amount of light you are getting per square foot is through the use of lumens. Wattage and lumens tend to go hand in hand, but can vary system to system. Even though lumens tend to correlate with wattage, it is the design of the light that can have drastic impacts on the actual amount of lumens emitted.

There are three factors to consider when deciding how many lumens you need. These are:

  • The size of the grow area
  • How many plants you have
  • How large your budget is

It basically comes down to this, the more lumens cast over your grow area, the stronger your cannabis plants are going to grow. Each plant will require an absolute minimum of 2,500 lumens. A standard 400W HID lamp will usually emit 45,000 lumens. This should be enough to comfortably grow up to 12 cannabis plants in a 1m2 area – with enough lumens to cause strong growth.

You will have to take the strain you are growing into account here as well, one large sativa may take up the entire area you would use to grow many smaller indicas. Meaning if you plant to grow a lot of sativas you will need a bigger area and more lights to cover them.

Whilst have 45,000 lumens within a 1m2 grow area will get you good results, having a light with a higher wattage that produces more lumens within the same area will help you achieve even better results. It all comes down to how much you want to grow, what lighting systems you can afford and what you are prepared to spend on electricity bills. The stronger the light, the more it’s going to cost you.

400W and 600W light bulbs are the favorite of indoor cannabis growers. Some growers even use light bulbs with 1000W. This is logical, when you consider ‘more light = bigger yield’. But watch out; the more Watts you use in your grow room, the hotter it gets. Especially with 600W and 1000W light bulbs the temperature can become way too high for your cannabis plants in your grow room. So be prepared to do some temperature control when using strong light bulbs.

An excellent way to measure the amount of light you are getting is through the use of lumens. Wattage and lumens tend to go hand in hand.