A comprehensive greenhouse lighting plan takes things such as crop needs, greenhouse layout and light intensity into account.
Photos courtesy of Growspan
Lettuce growers can often get away with using metal-halide fixtures since lettuce does not need to flower like other crops.

Growers invest a large amount of capital into their greenhouses, equipment and even automation to create an efficient and profitable grow. An operation could have the most high-tech equipment money can buy, but if they neglect their lighting, the grow can fall apart and the operation will end up losing money on energy costs and unhealthy crops.

Supplemental lighting is an integral part of any grow operation, and a proper lighting plan ensures that the lights are perfectly configured in order to deliver even, uniform light throughout the greenhouse in the most effective and efficient way possible.

There are many important factors to consider when designing a lighting plan, including light intensity, plant requirements, greenhouse layout, greenhouse cladding and more. Each of these elements influences the lighting inside the greenhouse in one way or another, so a lighting plan needs to consider all of these factors in order to be effective and efficient. A comprehensive greenhouse lighting plan takes things such as crop needs, greenhouse layout and light intensity into account to ensure for uniform, even light distribution over all plants for a healthy and thriving grow.

How to create a comprehensive lighting plan

Before getting into specific lighting plans, it is important for growers to know the lighting options they have and choose the best ones for their specific crops and greenhouses.

There are four types of supplemental lighting that are most commonly used in greenhouses:

LED: LED fixtures are one of the longest lasting and most energy-efficient greenhouse lighting options. While their upfront cost may be a bit higher than other options, they will provide energy cost savings to make up for it, so growers can expect a return on their investment. LEDs have a lifespan of about 50,000 hours and higher end models even provide flexibility of the color spectrum.

"A lighting plan should be designed by a greenhouse specialist with specific greenhouse lighting experience. — Janine Coppola

High pressure sodium: High pressure sodium, or HPS, fixtures are a type of high intensity discharge (HID) lighting, which means they give off a bright and intense light to crops. They provide a good spectrum of light to crops and are efficient and a popular choice among greenhouse growers.

Ceramic metal halide: Ceramic metal halide fixtures, another form of HID lighting, are similar to HPS fixtures. They offer a similar intensity to HPS fixtures, but provide intense blue or white spectrum light, and are well-suited for vegetative growth stages. These lights are ideal for locations that lack natural light.

T5: T5 fixtures are more efficient and compact than their more traditional, older fluorescent counterparts. These full spectrum fixtures are ideal for greenhouses with an absence of natural sunlight and are beneficial for large areas due to their efficiency. They also work well for propagation.

Growers need to consider the spectrum of light their crops need when choosing their lighting fixtures and designing their lighting plans. The spectrum of light necessary for growth varies from crop to crop, and different lights will generate different color spectrums.

For example, a lettuce grower might only need metal halide fixtures since lettuce does not need to flower like a tomato or cannabis plant would. Growers of flowering crops, on the other hand, would need high pressure sodium or full spectrum LED fixtures. Higher end LEDs work well for smart lighting applications, as the color spectrum can be adjusted or changed based on the growth stage of the crop. And light intensity can be dimmed for various stages of growth.

After lighting is chosen, it is time for growers to create their greenhouse lighting plan. It is important to note that a lighting plan should be designed by a greenhouse specialist with specific greenhouse lighting experience. This will ensure that the plan is designed for maximum efficiency and will properly function for the needs of the crops, while boosting the operation’s profitability.

When creating a lighting plan, growers should think ahead and consider the possible expansion of their operation.

3 factors you must account for

There are many factors that must be taken into account when designing a greenhouse lighting plan. Adrian Valois, greenhouse specialist at GrowSpan Greenhouse Structures, cites three key considerations for growers to keep in mind when creating their lighting plan.

“The first thing that you need to think about is your crop. Different crops have very specific needs when it comes to the right spectrum of light they need to thrive,” he says. “Second, you need to have a layout for your crops, so that you can maximize each light fixture being used. Third, you need to have the right wattage and coverage for each light.”

The greenhouse’s layout has an immense effect on its lighting plan, so growers should try to maximize each light by having a good crop layout. For example, if crops can be grown in a 2- by 2-foot area instead of a 3- by 3-foot area, growers can have 25 plants under supplemental lighting instead of 10. Based on how plants and equipment are situated throughout the greenhouse, lighting placement needs to be adjusted in order to reduce shadows and deliver the maximum amount of uniform light to the crops in the most efficient and effective way possible.

Equipment around the greenhouse or even the light fixtures themselves can cast shadows on the crops below, limiting the light they can take in. When lighting is not properly hung, rafters and purlins can cast shadows as well. It would be counterproductive for a grower to install light fixtures only for their shadows to hinder their crops from taking in that light.

Light intensity is of paramount importance when a grower is creating a lighting plan. The light intensity needed by different plants varies, and too high or too low light intensity can be detrimental. Finding the perfect light levels for the crops and the right light coverage will ensure plants thrive.

“Light intensity is more important than the number of fixtures. The right light will provide more coverage, resulting in less fixtures,” Valois says. “More wattage usually results in fewer light fixtures and same quality, so this is highly recommended.”

Another factor to consider is the heat that the lighting fixtures give off. Certain crops may benefit from added heat and growers may even end up saving some money on heating costs. Other crops may not need the heat, especially if the greenhouse is already located in a warmer environment. Growers should consider what temperatures their crops thrive under and how much heat their lighting choice gives off when designing their lighting plan.

“Heat actually helps a lot of growers who only need supplemental lighting during the colder months,” Valois says. “Having a good spread will also help reduce heating costs inside your greenhouse, especially if using high pressure sodium or metal halide fixtures, but you might have to place them a little higher than if you were to use LEDs.”

Different claddings have different light transmission rates, so growers should take their specific cladding into consideration when creating their lighting plan. A greenhouse that has cladding with a lower light transmission rate may need more supplemental lighting than a greenhouse that has cladding with a higher light transmission rate. Growers should also consider the R-value, or heat retention, of their cladding as their lights may give off heat that will then become trapped within the greenhouse if their cladding has a higher R-value.

When creating a lighting plan, growers should think ahead and consider the possible expansion of their operation. Keeping this in mind from the beginning will make the expansion process easier down the line.

“If a grower is expanding, keep in mind the coverage of each light fixture when doing so,” Valois says. “This could save growers a lot of money if they expand by the right amount.”

Key grower takeaway

A comprehensive lighting plan considers every aspect of the greenhouse and the crops to ensure the even and uniform distribution of light for the healthiest grow possible. With all of these factors being taken into account, the perfect lighting plan can be designed for an efficient, effective and thriving grow.

Janine Coppola works for GrowSpan Greenhouse Structures. For more information visit www.GrowSpan.com.