Lux Levels

What are lux levels? Lux levels are another way of measuring light output. Where PAR (photosynthetic active radiation) shows what light plants take in at various wavelengths, lux levels deal more with visible light.

Although plants use a lot of light that isn’t visible to us, there are plenty of advantages to measuring lux levels for hydroponic plants. It’s actually quite surprising how much we can learn about from this measurement, and how much our plants can benefit when we do.

Are Lux Levels Important for Growing Plants?

There are a few main ways of measuring light, at least when it comes to hydroponics. You have lumens, lux, and PAR. Lux levels actually consider the amount of radiance or illumination that shines on a given square meter. Lumens simply measure the output of light. When you’re growing plants in hydroponics, it’s important to make sure plants get the most out of the light you provide.

While lux levels may not be the end all be all of your lighting schematic, they do give you important information about your grow situation. Plants receiving less lux than others may not thrive, while those receiving too much may end up dehydrated and burned. Most people think that because lux is used to describe visible light, it doesn’t have any bearing on how well plants take it in. It’s true that plants need certain wavelengths of light to thrive. But it’s also true that if you can’t see how much light each plant gets, some may not get enough and won’t grow as well. 

In short, you can grow plants without measuring lux levels. But if you want to make the most of your harvest, you should do it. 

Why measure lux levels?

It’s common enough for people to solely focus on PAR (Photosynthetic Active Radiation) when they’re growing plants. However, lux levels can tell you a lot about how much light your plants are getting. It might surprise you how much a small adjustment in your grow light’s positioning can make. 

We all know that certain plants can tower over another, preventing it from getting enough light. That’s not always the biggest problem though. Sometimes your lights just don’t sit right, and don’t give the same amount of light to each plant. It’s hard to achieve perfect, equal lighting here. Still, it isn’t impossible. If you measure lux levels close to your plants, you can see exactly how much light each plant gets. Then, adjust your grow lights accordingly. 

Lux meters are surprisingly affordable. When you have a serious interest in hydroponics, there are plenty of things you’ll invest in. A lux meter is a small one for the increased yields you can get from using it. 

Not only does it help you position your lights, it also tells you more about your grow lights themselves. 

example of a lux meter

Learn more about the types of light plants need in this guide.

Does Wattage Indicate Light Output?

Wattage may seem like just another measurement out there to confuse you, but it isn’t. However, it does get confusing when you realize higher wattage doesn’t mean it’s a better light.

Does wattage indicate how much light a bulb produces? No. Wattage is simply a measurement of how much power something needs to work. The longer answer is that wattage actually shows how many joules (a measurement of power) per second are used. 

Watts are most helpful when you’re trying to find an energy efficient grow light. 

The clearest example of why you shouldn’t rely on wattage alone to pick your grow lights is LED. Light Emitting Diode (LED) lights are highly efficient. Not only that, they can also produce more light using less energy, and provide a full spectrum of light. These are a newer type of light, so they’re not built like your typical light bulb. 

Leafy greens under LED grow lights

LED lights have a special chip, driver, heat sink, and a unique setup. Because of that, more watts might actually inhibit your grow more than help it. While these lights are known for staying cool, they still produce some heat, even if it’s very little. As wattage increases, so does the heat in the circuit board. In turn, the light’s efficiency actually goes down. 

Measuring LED Grow Lights

When you look for LED grow lights, you’ll see several different measurements. Some manufacturers provide measurements only in watts, which doesn’t do you much good. 

Other measurements include:

  • Lux 
  • Luminous Flux
  • Lumens
  • PAR
  • Foot Candles 
  • Candelas

That’s a lot for anyone to take in, let alone compare. Here’s what each term means:

Lux: Lux is the measure of visible light that falls on a certain area of measurement, usually a square meter. 

Luminous Flux: Luminous Flux sounds like a shorter way to say lux, but it isn’t. It’s actually a measure of how much light a source gives off. Not how much lands on an area. 

Lumens: Lumens is a way to measure luminous flux. Again, it measures the amount of overall light given off by a certain source. That’s why you typically see lightbulbs rated in lumens as well as watts. 

PAR: PAR stands for Photosynthetic Active Radiation. Essentially, it shows the wavelengths plants absorb for photosynthesis, whether it’s visible to the naked eye or not. 

Foot Candle: Foot Candles are a way to measure how much light is seen on a surface from about one foot (30.5 cm) away. It’s nearly the same as lux, but uses Imperial measurements rather than metric. 

Candela: Candelas are very similar to luminous flux. It measures the light given off by a source, but considers the particular direction light is aimed at. 

Here’s a chart showing conversions between all the measures of illuminance.

Lux levels and measurement conversion

You may notice that there are many repeating figures. That’s because many of the different measures are quite similar in what they tell us. However, because many represent directional lighting, or lighting within a certain surface area, each has its own application. 

To measure an LED light’s output, you have to look beyond watts. Lumens are one of the most common units manufacturers use when measuring their lights. However, we recommend considering lux levels when you choose your grow lights. The reason is that you’re not simply illuminating an office or building and making sure it’s bright enough.

Look at our guide on measuring LED grow lights for more info!

You only have so much space in your grow area. Lux is what measures illumination, not in general, but to a specific area. If you can only have so many plants in a single area, you need to ensure you’re making the most of your light.