edding plants and leafy greens, and high light plants like full sun bedding plants, cut flowers and fruiting vegetables. Plants such as tomato, pepper, cannabis and roses are recommended to have very high daily light integrals for quality production and yield. For example, if you have less than 5mol/m2/d1 you would need to supplement up to 30mol/m2/d1 for cannabis as it can require up to 35mol/m2/d1.
While suggested DLI varies depending on crop – this guide from Purdue University outlines minimum and recommended DLI for many popular greenhouse crops. Aside from low light plants such as ferns or orchids, many medium and high-light crops will see quality and yield increase with increasing DLI. Plants receiving low daily light integrals tend to be of lower quality and will stretch in search for light.
HPS vs LED for Northern Growers
Lighting is one of the most important factors for growers in a Northern climate where winter light levels are low. Choosing the right lighting system that works with your growing space is imperative to ensuring a successful crop.
LEDs have been shown to save money in the long run by cutting down on electrical costs as well as having a longer life when it comes to burning hours and replacement. However, in many cases we find growers who are located at Northern latitudes continue to use HPS (high pressure sodium) lights in their crops. A reason for this is that LEDs do not emit as much heat as HPS lights, and many plants such as peppers, cannabis and tomatoes tend to benefit from the radiant heat emitted by the HPS lamps in the winter. The heat emitted from the lamps is not an efficient way to heat a greenhouse, but the radiant heat provides a great benefit to the plants. Please take note that you cannot rely on HPS lamps to heat a greenhouse, but they can help cut down on costs.
On the other hand, LEDs while energy efficient, do not emit radiant heat, therefore more heating is required during the winter months to compensate and the heating costs can outweigh the energy savings of the luminaires themselves. Another factor to take into consideration is light uniformity. This depends on how your greenhouse is set up but in general HPS lamps will provide a broader, more uniform light output pattern and LEDs tend to have a more focused illumination. Since we manufacture and sell both HPS and LED luminaires, we do not have a bias towards either and are motivated only to sell you the best lighting system that works for your greenhouse.
Spectrum and Intensity Considerations
Plants require light in the photosynthetically active radiation (PAR) range of 400-700 nanometers for proper development – and not all lights are created equal when it comes to PAR and light quality. When thinking about adding LEDs to your growing operation we recommend starting with a trial area, so you know what to expect if you decide to adopt the lighting on a larger scale. We have worked with growers in the past who have installed a competitor’s LED system, to have them come back and buy additional luminaires from P.L. Light Systems because their existing lights did not have the full spectrum the plants needed and/or the light intensity was not enough to hasten the plant’s growth. Plant varieties will all react differently to variations in light spectrum and light intensity and it’s important to understand what these reactions and outcomes are before investing in lighting for an entire greenhouse.
Considerations for when choosing a lighting system
Many things should be taken into consideration before investing in a lighting solution. Consider how lighting might affect the environment of a greenhouse and any changes that will need to occur. Parameters such as watering, heating, nutrient uptake and humidity may be affected and need to be adjusted.
Some crop and environmental considerations to think about when choosing a lighting system:
- What is your target DLI for your crop?
- This chart from Purdue University gives recommendations of DLI based on crop. By deciding what your target DLI is you can better choose the amount of light