Plants need light to grow. A LOT of light.
The full, noon sun provides 300 watts of light per square meter to us on earth. Being that light bulbs tend to be sold with ‘watts’ measuring the electrical usage and not the light output which is measured in lumens, lets describe sunlight differently. The sun provides 200,000 lumens of light per square meter.
A 60 watt incandescent or 15 watt Compact Florescent provide about 900 lumens of light. Light bulbs do a really lousy job of converting electricity into light.
A room that appears to be brightly lit with electrical lights is actually pretty dimly lit when compared to the light the sun brings to the party.
Now that we have an apples to apples understanding of how much light the sun provides, lets explore plant lighting.
Plant Lighting Requirements
Different plants require different amounts of light. Plants that are adjusted to growing in full sun will NEED very bright lights to grow well, while plants that are adjusted to dappled shade won’t do so hot under bright light (think full sun bright) conditions.
Plants made for bright sunlight tend to have smallish leaves, while plants that are made for shade tend to have bigger leaves.
By selecting low light plants, you can reduce the need to provide additional lighting for your plants.
Lighting Considerations
Light fixtures that are designed to provide a lot of light to a small area tend to be quite hideous. Not just because the fixtures are ugly, but because they can literally be hard to look at. The human eye can adjust wonderfully to light changes, but looking around a relatively dark room towards a bright source of light can be painful.
Often times you can get more plant growth by extending the length of the ‘day’ with artificial light, however plants do need a period of dark to ‘sleep’ just like we do (You can look up the Calvin Cycle if your are curious). It is often times better to go brighter for a shorter period of time to get healthier plants.
It’s most convenient to use a light timer to control your lighting. Timers tend to forget less often to turn the lights on and off at the right time than humans do.
Lighting Options
There are 4 options when it comes to lighting. What you choose will depend on what you have for space, lighting requirements, and aesthetics.
Natural Lighting
As pointed out at the top of this page, the sun provides a crazy amount of light. If you can put your plants in a window that gets sun, great. East and West windows often work well for low to medium light plants while you may need a south window for full light plants.
Natural lighting around a fish tank is usually a bad idea, as the tank will grow green with algae growth. If you can shield much of the sunlight from the water, you can reduce the algae growth.
Incandescent
These work under the premise that if you get something crazy stupid hot, it glows. Being that these get hot first, then glow, they aren’t very efficient.
These are what Edison invented, so they have been around for a while. Most nice looking light fixtures where invented with these bulbs in mind. If you want to keep your plants warm, this is a good selection, otherwise pick another type of light as these can be expensive to run, and the other light bulbs can fit these light fixtures.
There are types of incandescent light bulbs that do work well for plant growth. However, Metal Halide bulbs are very big, very hot, and usually very ugly, so you probably don’t want to have one in your living room.
Florescent
These are glass tubes coated with phosphors – kinda like glow-in-the-dark paint, except it’s glow-when-you-juice-it-with-electricity paint. Being that these don’t need to get hot before they can glow, they are a little bit more efficient.
These tend to be the go-to light fixture when growing plants. You probably already have one on your aquarium, so it’s a natural fit.
The tube fixtures are cheap and plentiful if a bit lacking in appearances. You can get nice looking fixtures that are designed for kitchens. For small spaces, several under counter light fixtures will work, and for larger spaces, a nice ceiling light or 4 will work nicely.
You also get Compact Florescent Light (CFL) bulbs that fit in regular, nice looking light fixtures. You can find bulbs that sre 55 or 65 watts – not 55/65 watt equivalent – at most stores that sell a good number of light bulbs. These things are much larger than what you may be used to for a CFL light bulb.
The trick to these bulbs is that you can get them close to the plants – within 6 inches of the tops of the plants. The fixtures you want to pick should reflect all the light in one direction – traditionally down – but for our purposes, towards the plants.
A 2 bulb, 4 foot, T12 shop light fixture about half a foot above the plants is enough to make lettuce grow. It’s not going to grow very well as there isn’t quite enough light. Doubling that amount of light will give you good results.
The most annoying thing with Florescent light bulbs is that they loose about 30% of their brightness over the first 6 months of usage. To continue to get good plant growth, you need to replace light bulbs even though they look to be working perfectly fine, thank you very much.
LED
Light Emitting Diodes work by applying the break down voltage to very specific element combinations causing the collapse of very specific electron shells emitting light at very specific wavelengths. You are basically half way to a laser beam except you don’t have the really cool properties that the ‘beam’ part of a laser. These create light without the need of getting things hot or juicing glow-in-the-dark paint, so they are a bit more efficient yet.
The RED/BLUE LED lights are the latest and greatest in lighting technology. NASA did a study and found that if you used a combination of RED and BLUE LEDS, you can get great plant growth with a minimal of energy input. This is the most efficient way to go as you can provide only the wavelengths of light a plant needs for photosynthesis. An effect of this efficiency is that the plants absorb most of the light that reach the leaves, leaving the plant looking black. This is all fine and dandy if it’s Halloween or you are into the whole goth scene, but most of us will use the white LEDs so our plants look normal.
These fixtures are still very expensive compared to the other choices. There are now cheaper ones available, but they generally aren’t as good as the expensive ones. They may be good enough for your needs though.
White LED lamps are built one of two ways, they use a phosphor the same way florescent lights do, or they are really several different color LEDs in the same spot that look white when the light is combined. White LED lights look good to the human eye, but generally aren’t great for plant growth.
LED Par30 (parabolic reflector) Flood Lamps can be a good way to go. They focus a lot of light into a small area. So while they may not be the perfect light as far as plant growth go, they do provide a lot of light that looks good to humans.
