A look at lights

Confused about lighting your plants? Not sure about the differences between HID, LED, plasma, daylight and induction lighting?

It seems everyone has different ideas on how to light greenhouse and growth chamber crops. Let’s look at the different options and see what works best for your application. Here are some questions we get asked from people on a weekly basis.

Q: Why do I need to light my plants with supplemental lighting?

A: Plants need energy from the sun or a light source that gives them the PAR (Photosynthetic active radiation) to continue to grow. Without good lighting, plants will grow slow and give lowered production. When this happens they are more susceptible to diseases and insects. You can give plants more water and nutrients, but without light, plants suffer.

Q: Can I use just any light source?

A: Plants need PAR light for photosynthesis. Different lamps produce many different spectrums. What you want is a good plant light that gives plants the spectrums they need for optimal production.

Q: I see a lot of new products on the market. How do I decide what I need?

A: The first thing to look at is what are the major growers using? If it has a proven track record such as HID lighting does, then we know that this technology works for plant production.

Q: I know that HID lights are used by most major growers, but what about the newer stuff on the market. Will they work for my greenhouse?

A: When we look at other lighting fixtures we look for a few important details.

Is the reflector being used small enough to allow natural light to get to my crop? Many times people think a big reflector is a good thing. Why block your primary source of light? You want as much natural light to get to your plants as possible. Large reflectors are bad.

Does the light have enough intensity for high mounting heights? Right now LEDs are replacing fluorescent fixtures in growth chambers and in multi-shelf applications. While they are great energy savers, we just don’t see enough intensity from these fixtures to mount them up high in a greenhouse. Some that do claim high intensity are costing $1,600 each or more, and this is a very expensive proposition for a greenhouse.

Other LEDs would block more natural daylight to get the recommended amount of fixtures needed to match a single HID fixtures output. As technology gets better and prices come down, this will be a viable option.

Are the fixtures producing uniform patterns? We want uniformity in a greenhouse. I have seen people buy cheap high-bay lights for the greenhouse. While these were used years ago (and still used in older greenhouses) the industry went to horizontal bulbs many years ago. A round high-bay reflector gives a round light pattern. Round patterns are harder to get uniform than a rectangular pattern. Look at a six-pack of soda. The cans touch but there are still gaps between the cans. You have to use more high-bay fixtures closer together to get a uniform pattern. With horizontal-mounted bulbs, we get 40 percent of the light straight to the crop, the rest has to be reflected. With vertical bulb high-bays, you have to reflect 100 percent of the light. Hope your reflector is clean.

So you see, all lights are not the same.

Q: What about induction or plasma lights?

A: Induction lights are fancy fluorescents. They use large hoods and magnetic pulses to excite the gases in the tubes. These might be good for indoors or light carts, but block most of your natural light. Plasma lights can be very expensive. They give more of a full-spectrum light to plants. A better and cheaper alternative is the new “daylight” fixtures on the market. These offer a “daylight” spectrum, and the bulb can be switched to give more PAR to your plants. Some like daylight spectrums because they see more natural growth and they can do research that is similar to growing under natural light.

Q: So what should I use?

A: HID lighting for greenhouses is going to be the standard for a long time. While some complain about the heat from an HID light, it can help offset gas usage to heat a greenhouse in the cold months when they are used most. These have been the workhorse of the industry for many years.

LED lighting is great for tissue culture, multi-level growing, lettuce production and areas where we can stay within 24 inches of the crop. They can be used now to replace fluorescent fixtures in growth chambers and on light carts. They can also be used over propagation benches. They can save on your electric usage, and they are constantly getting better. We are also seeing benefits to interlighting large crops with LEDs.

Ask your lighting rep if this is a viable option for you. Do your research. I have seen some exaggerated claims of LEDs, plasma and induction lights verses HIDs on websites. If you’re unsure, call one of the experts in the lighting industry.

James Grouzos is a sales engineer for P.L. Light Systems.