Choosing the right LED grow light for your greenhouse

If you have decided on LED lighting for your greenhouse, congratulations. You are choosing an energy-efficient lighting option that will create a much better environment for your plants. However, choosing the right LED fixture for your greenhouse can be a daunting task – especially if you are new to LED lighting. 

Below, California Lightworks will go over some critical factors to consider to help you get started. 

Why do greenhouses need supplemental lighting?
While greenhouses benefit from natural lighting, this doesn’t mean they don’t need supplemental lighting. Without extra lights, you’re entirely reliant on weather conditions – which is quite a gamble, especially if you have schedules to maintain. Also greenhouses typically only get an average of 75-80% of the DLI outdoors on the plants inside.

So during low levels of solar radiation, supplemental lights are vital to ensuring healthy crop production and even yields. This is most obviously helpful if you are growing during the winter months, but LED lights can also help during overcast days in the spring or summer. Light intensity outdoors varies significantly throughout the year, and LED lights can help you maintain a consistent light intensity year-round. With a properly designed LED system, greenhouse production can approach indoor yields even in the winter.

Shadow effect
A major point of concern for greenhouse lighting is the shadow effect. Even the slimmest fixtures cast shadows, which can impact plant growth and cause uneven distribution of light. So the smaller the light per uMol of output, the less sun you will lose for that LED light. 

The MegaDrive™ Greenhouse Lighting line has the LED drivers located remotely in the Megadrive, which mounts on the wall. This elimination of the driver reduces the square inches of shade created by the light by around 25%, which means 25% less shading compared to lights with integrated drivers.

In numerous comparisons to top-tier LED lights, the MDL-400 fixture has an average of 30-40% less shade area in square inches. In a normal 40×100 greenhouse bay with 200 lights, that 40% less shading is literally enough extra sun to equal the output in PPF of 15 more MDL-400s!    

Shading is a commonly overlooked aspect to greenhouse lighting, and it has a significant impact on your productivity. This along with dramatically lower installation costs is a major benefit of the remote driver design employed by the Megadrive. 

Estimating operating costs 
Operating costs can fluctuate greatly depending on individual needs. It is also important to note LEDs have a higher upfront cost than traditional HID lighting. However, the long-term costs of running LEDs are much cheaper as they’re vastly more energy efficient. 

To determine your operating costs – and therefore a rough budget for lighting – you’ll need to consider various factors. How many hours will your lights operate per year? Will you run your lights throughout the whole year, or only at certain times of the year? Knowing your daily light integral (DLI) – which we’ll go over in the next section – can help you answer these questions. 

You also have to consider installation costs. Greenhouses typically have to hire outside help to install lighting and – if you’re renovating an older building – there may be other renovations you need to make prior to even installing LEDs. Extensive electrical upgrades are often required that can cost up to 50% of the cost of the fixtures.

MegaDrive Greenhouse Lighting Technology has the potential to reduce installation costs by up to 80% and fixture costs by up to 30%. Operating costs are also 50% lower than HPS grow lighting. 

Your daily light integral
We have covered this before in a bit more detail here, but for a brief recap, daily light integral (DLI) is the total amount of photosynthetically active radiation your plants receive each day from the sun. As greenhouses have varying light levels due to both natural and supplemental light, knowing your DLI is important to ensure you’re purchasing the proper LED fixtures at the proper light levels. 

This link provides a helpful tool that estimates DLI in various locations for each month of the year throughout the United States. This gives you your baseline, but you will have to factor in light lost through greenhouse transmission. For example, you’re growing a type of plant that thrives with a DLI of 16, but the average DLI in your area in the winter is 12. Greenhouses – on average – transmit only about 65% of that light. So, in the winter, your plants are only getting a DLI of 10.4. So, 5.6  of your DIL needs to come from supplemental lighting to ensure even yields across the year. 

Once you know how much DLI must be generated from supplemental lighting, a quick calculation can help you determine the rough PPFD range you should look for in an LED fixture. Multiply the amount of supplemental DLI by 1,000,000 and divide that by the number of hours you’ll be running your lamps per day. Then, divide that number by 3,600. 

Going back to our above example, say you’re running your lights 24 hours a day. Calculate 5.6 X 1,000,000 divided by 24 divided by 3,600. This comes out to roughly 65 umol, so keep that range in mind when choosing LEDs. 

However, this is a very simplified example. Obviously, throughout the year, you will have to tweak your calculations and account for factors like weather fluctuations. There is also such a thing as too much DLI. Most plants can only handle between 40 to 50 DLI before experiencing light stress. Sudden weather changes could therefore harm your yield. 

One solution is to look for a light with photosensor control (available in our California Lightworks MegaDrive Greenhouse line). This allows you to input a user-selected PPFD threshold that directly correlates to your DLI target. The photosensor will sense varying daylight and weather conditions and automatically supplement light to meet that threshold. 

Softer factors 
After considering the more technical aspects of LED lighting, there are some softer factors to consider when choosing a manufacturer. 

First, do you spot any obvious red flags? A good provider will provide information such as PPF, for example, lighting layouts, third-party photometric lab results, the IP grade, and safety certification. Extraneous or dubious information – like the number emitters or outlandish crop yield improvement – is often an indication a manufacturer is trying to make a subpar product look better than it is. 

You should also look for good signs as well. A warranty is key when buying a light as even well-made machinery may sometimes come with factory defects. Other perks – like a free consultation or discounted installation – are often helpful as well. 

LED lighting for greenhouse: The bottom line
Choosing the right LEDs for your greenhouse can be a daunting task that entails a lot of research – especially for beginners. However, it’s well worth the extra effort. A high-quality LED light can last for decades, so make sure to choose the best option for your needs. 

"At California Lightworks, we are always here to help. If you have any questions about LED lighting for greenhouse, reach out here and someone will be in touch shortly."