Ask the LED lighting expert: Do Greenhouses need supplemental lighting?

Ask the LED lighting expert: Do Greenhouses need supplemental lighting?

Greenhouse growing has been around for centuries, but in recent years, supplemental lighting has been used to increase crop production – especially during the fall and winter months.

So, the question is, do greenhouses need supplemental lighting? How can it be used? What is the future of greenhouse growing and supplemental lighting? And why does day light interval (or DLI) matter?

When considering supplemental lighting in a greenhouse, there are a few things to consider. It can definitely increase crop production and take some of the risk out of cloudy or rainy days – even in the summer. And it can definitely cut the length of a growing cycle, which can also produce a higher-quality crop in a shorter amount of time (meaning you can grow more in a year – increasing yields and profits).

To learn about how a greenhouse grower can benefit from supplemental lighting, let’s learn about day light intervals or DLI. 

DLI is the amount of daylight your crop gets during the day. Indoor growers have total control over this variable; greenhouse growers have to do some calculations to get the right formula, because their primary light source is the available sunlight.

In greenhouse growing, growers have to consider the time of day, the season, the weather and more to get plants the DLI they need to flourish. Each plant has its own unique DLI needs and the DLI a geographic area fluctuates with the seasons, weather conditions and more. 

In Columbus, Ohio, for example, the DLI in the winter is about 10-15 mol/m^2/day a day. But a plant needs much more than that to grow, so growers who grow in greenhouses have to bring the DLI up artificially through supplemental lighting. In Columbus, in the mid-summer when lighting conditions are ideal for most plants, the DLI is 40-45 mol/m^2/day. 

It’s important to note that these numbers are general and so growers should do their own calculations to determine what their particular crops need to produce flourish. For example, a tomato plant will need less DLI than a tropical plant that is used to a longer day for most of the year.

Generally, the light inside of a greenhouse is reduced about 35-50% from what is available outside. That also means that greenhouses average 50-100 µmol of light. This is when additional lighting can take over. Shadowing is a major factor for greenhouse growers, and managing the movement of cloud cover or inclement weathers with supplemental lighting is a great way to maintain uniform growth and adhere to growing timelines. 

Shadowing isn’t limited to cloud cover, but can also be introduced by the supplemental light itself. It is important to consider the physical size and shape of the supplemental lights to reduce shadowing the plants below. Most greenhouse cultivators choose long slim profiles for their supplemental lighting, like the Linea because the design minimizes shadowing. 

As with any growing operation, light uniformity is also an important factor to consider when you are designing or installing supplemental lighting to a greenhouse. There are computer modeling systems available to make sure light is evenly distributed over the entire plant canopy. 

LED lights really shine as supplemental light sources for greenhouses, as they require no warmup period, like older-technology HID lights. They can be turned on and off and provide instant light when a cloud passes over, even controlling lights in a specific area or quadrant of a greenhouse when only a portion of the space is impacted by cloud cover.

In a greenhouse, it is possible to give plants too much sun as well, especially for younger plants during the propagation cycle. Thoo much light is usually managed with shades in a greenhouse. And all plants need a rest period each day (as do humans) and while scientists aren’t exactly sure why, there is evidence to suggest that running lights 24/7 is detrimental for a plant. 

The Key Takeaway

Supplemental lighting systems for greenhouse growers can have many benefits. Depending on where you are growing – and the time of year – supplemental lighting can increase growth rates, yields and profits by keeping the light levels consistent for these great results.

It can also extend the growing season.

While lighting options can be costly, with careful consideration and planning, the right lighting system will pay for itself eventually.