Building a DIY Hydroponics System Part 4: Lighting
This is Part 4 of a 7 Part Series of how to build and manage a DIY Hydroponic Lettuce System!
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For use in the home, natural light is generally insufficient to grow significant amounts of produce. The two main types of lighting we've used are T5 fluorescents and LED.
Fluorescents are nice because they are relatively cheap and easy to find. T5 fluorescent tubes are among the most efficient fluorescents and are popular grow lights. We started our journey using fluorescents and they worked well. If you want to start cheap and simple and already have a fixture laying around, go with T5s. We would recommend a minimum of a 4 ft, 4-bulb light such as this one but a 6-bulb fixture is even better for a 2 rail system. The primary disadvantage of fluorescents is that they use more electricity than LEDs. Each bulb is 54 Watts.
At this point we've switched over completely to LED lighting. We've found LEDs to be much more energy efficient and they've produced better yields for us - a win-win. There's a lot of options for LED lighting, but we started by replacing our fluorescent bulbs with Active Grow LED bulbs that fit into a regular T5 fixture and produce white light (as opposed to the purple light produced by some LEDs). Each bulb uses 24 Watts - less than half the electricity of the fluorescents. The downside is that they are more expensive, but in most situations the higher cost will be recouped by the energy savings down the road. Active Grow also sells a full fixture with LED bulbs which we have as well.
We are also using a Mars Hydro TSL 2000 LED grow light and have had good results so far. It is much more compact and less weight and yet is extremely bright! It has a dimmer which allows us to adjust the lighting to the intensity we need. If you want to jump straight to LED this would be a good option. It has plenty of light coverage for a 2 or 4 rail system. It also includes adjustable ratcheting hangers which is nice if you are hanging from a ceiling. At full brightness this light is rated for 300 Watts but uses less when its dimmed.
Another great option, especially for vertically-stacked systems, is individual LED tube fixtures such as these. Instead of a fixture with 4 or 8 tubes built in, each of these fixtures can be placed separately and linked together. They are the lowest-cost option we've found and they work great. For lettuce, you should just need 1 fixture per rail, placed about 15 inches above the top of the rail. These hang really nicely from vertical racks with the included zip ties, but they would be harder to hang from a ceiling or similar because you have to hang each one individually.
From experimenting with height, it seems that having the light 15-18 inches above the top of the rails works well for both LED and fluorescents. For hanging the lights, we have hung the lights from their built-in hangers if the location allows for that (see support structure for more info on that). However, in cases where the hanging point is higher than needed, we've used adjustable ratcheting hangers. They provide quick height adjustability and allow for easy experimentation.
To control the lighting cycle and reduce the amount of work for us, we use a simple daily timer. This allows us to have the plant lights to turn on and off automatically so we don't have to remember to do that. They are inexpensive and provide a simple way to create a consistent lighting schedule with very low maintenance. We set our timer to turn on at 8 am and turn off at 10 pm, which is 14 "on hours" per day.
Be aware that artificial lighting will create some heat. In our climate this is totally fine in the winter but can raise the temperature too high in the summer months. To combat this, we've used a small clip fan to push out warmer air that collects between the light and the lettuce. The fan can be plugged into the light itself so it only runs when the light is on. A fan can also help grow rates as it circulates CO2 around the plants, promoting photosynthesis. Our lettuce seems to grow best between 60 and 75 degrees, though it can handle up to 80 degrees for short periods of time. Warmer days will cause the plants to use more water.
We have not tried the system with natural outdoor lighting, such as in a greenhouse, but that should work well. If you try it outdoors, let us know how it goes!
Next is nutrients in Part 5!