This is a simple DIY way to make a reflector for a compact florescent (CFL) bulb.

There are many situations where you are lighting a plant and half the light coming from the bulb is going out your window, on the floor, or into you living room. A lot of this wasted light can be redirected back at the plant with a simple reflector.  With CFL’s the best light comes out the side of the coil, therefore a standard shop light reflector is not very affective. Fortunately it is possible to make a  effective CF reflector in under 10 min.

You will need:

1- 16oz beer can (12oz work, but not as well for bulbs over 15 watts)

1- CF bulb, I used a 26watt one

1- Clamp light (this will work for other fixtures too)

tools:

needle-nose pliers

tin snips or scissors you don’t care about

pocket knife

Step 1-

Take apart clamp light. With out a bulb in it (and not plugged in!!!!) twist the reflector off. It is threaded into the plastic, and it should come off in 3 to 5 revolutions. Next loosen the wing-nut until everything falls apart. You should now have something like in this pic:

Step 2-

Cut up your can. I started by poking a hole with a pocket knife, then attacked it with scissors. First I cut a strait line the length of the can starting and ending just before the metal starts to curve in. Next I cut off the top of the can. On the bottom of the can I cut a slit almost half way around on each side, leaving about 1/2in. on the opposite side as the slit.

It should now look something like this:

Step 3-

Cut a hole in the bottom of the can that the light fixture will fit into.  I did this by poking a hole with a knife and then pulling back the metal with pliers.  Notice in the picture that the hole is not centered, instead it is located closer to the side which was cut. This will give more room for the bulb.

It is also important that the hole is not much larger than the plastic fixture. When opening the hole, the extra metal should not be removed, as it is necessary for the next step.

Step 4-

Put the clamp light back together, with the new reflector.

Slip the new reflector over the plastic fixture, and bend the excess metal so that is touches the plasic. Then reconnect the bracket that connects the clamp to the fixture so that it compresses on these flaps of metal. This is what will hold the reflector to the fixture.

If you are not using a clamp light this connection could be made with a hose clamp, or my favorite thing; annealed steel  wire.

Step 5-

Fold the cut edges of the reflector.

Be careful with this step, it is sharp! Gloves may be a good idea, though it’s not as bad as most sheet metal, as aluminum is rather soft.

I bent a little under 1/2 in. of the edge over. This makes the reflector much stiffer, allowing you to bend it to the form you want.

At this point the reflector could be painted white, or better yet coated with silver Mylar. This can easily be attached with spray adhesive. Just cut the Mylar to size, spray, and stick it (read the directions on you spray adhesive)

Step 6-

Test it, and tweak it.

Bend the reflector so that it shines the way that is most useful for you.

For larger bulbs, like this 68watt CFL, a coffee can can be used.

The answer is generally, yes, you probably do need to supplement the light coming into your window in order to grow light-loving vegetable plants.

Testing light in my window with a foot candle light meter. Good light, but not enough of it long enough.

If these plants are going to be nutrient packed enough to be worth your while growing them and investing all this time, you should give them the light they need to photosynthesize and process the nutrients you are feeding them.

Lots of stem on this leggy arugula plant

Plants that do not get enough light grow “leggy”– they are all stems and the leaves look like they are perpetually reaching out for mooooore liiiiiiiiiight pleeeeeeease. Even my South facing unobstructed windows are not really getting enough light this winter and my arugula is getting looooooooong in the leaves.

Most of the information on lights we have been working with comes from the rather prolific specifications in

Gardening Indoors with Soil and Hydroponics by George F. Van Patten.

Windowfarms Light Policy
We have decided to use CFLs (and LEDs soon, as they become more affordable) because the big grow lights used in greenhouses and by pot farmers are simply not viable to live with in city apartments and frankly just use too much electricity.

Instead the windowfarms project has been focused on making the most efficient possible use of consumer grade CFLs. We are not using just any old CFLs. We have found the ones that are only recently available on the market most likely to grow vegetable plants through all stages of their lifecycle.

Lighting for plant growth is a complicated science and I will not burden you with understanding anything more than the fact that 4 factors are important for growing with CFLs under these conditions:
1) The Kelvin color temperature of the lights- The color of light produced by the sun changes over the course of the year and plants are tuned into these changes. Light color triggers them to enter different stages of growth, so we want to be careful about light color. Consumer brands use lots of different names like soft white, bright white, daylight, full spectrum. Don’t go by the term alone. Find out the color temperature (marked with a K). We have been using 6500 K bulbs and have produced healthy flowers and fruits in several species. Between the natural light coming in your windows and the artificial light, we’ve probably got a pretty good spectrum.

2) Wattage- This boils down to the strength of the lights. We want them to be strong. Thus far, we have produced good results using 27 Watt actual/100 Watt incandescent equivalent bulbs. We may find that we can go down to 75 watt equivalents (19 actual watts) or below depending on the array and proximity. This needs to be tested!

3) Proximity to plant- Van Patten claims, ”
Light from CFLs fades fast and must be placed close to plants. The bulb produces very little heat and can be mounted about 2 inches(5 cm) away from foliage to achieve best results.” So, we have tried to make the lighting moveable so that as plants grow, they are always within this distance from the bulb. We add in fishing wire as trellicing so that we can movethe branches if they try to grow too close to the light and start burning themselves (Plant thinks- yay! i have fnally arrived at the sun. Ouch!! It’s hot!).

4) Duration at each life stage- Just like teen humans need more sleep, adolescent plants need more light than adult plants do. Think about how plants are young in the spring when the days are longer and then the days get shorter again in the fall during harvest season. We use timers to control the lights, sometimes leaving the lights on longer than the sun is out. For more, read Van Patten’s Photoperiod section on page 88. You need to learn a little bit about the kind of plants you are growing and their natural best growing conditions, which you will then mimic with your setup.

Here are the specs on the bulbs we use. We have been using them because they are available all over the country at Home Depot and they fit our requirements. However, please feel free to find similar brands and post them here for others.
Blue package marked 100 Watt at Home Depot
N:Vision brand
SKU 599-526
27 Watts (Package says equivalent to a 100 Watt incandescent bulb)
Kelvin color temperature= 6500K (according to customer support) but marked 5500 K
120 V 60Hz 0.450 A

Supposedly these are available with globe covers but I have never found them. That would be rad because it would keep plants from singeing themselves.

This is my “work” farm.  I started it last week and already have two sprouts in it — rosemary and violas.  There is a desk lamp shining a CFL on it (on a 12 hour timer).

We have a second one (which was the first) here at home but I can’t find the photos of it right now (and am a bit too lazy to take a new one.

I saw a post about the window farms on Gothamist and just HAD to try it.  Got to say, it’s fun!  Folks walk into my office and are incredibly curious about what this curious structure is.

My husband and I are designing a larger farm for our living room window and will probably build it over the winter break (we are teachers).  Our major problem is getting the soda bottles since we use the SodaStream carbonator fr our soda needs and don’t drink bottled water.