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Starting your seedlings from seed can be frustrating.  Major complaints are that seedlings either do not sprout or they get very tall and spindly.  A light box can help with both problems.  

MATERIALS
  • a wooden melon crate  or other box 22" x 13" x 13"
  • plywood 22" x 13" x 3/4"
  • a fluorescent ballast for two 15W tubes*
  • 4 bi-pin fluorescent lamp holders*
  • 2 15W fluorescent tubes
  • grounded extension cord
  • wire nuts
  • flathead screws 6 x 3/4"
  • white faced corrugated or white paper
  • 24 hour timer
TOOLS
  • Drill & bits
  • Screw driver
  • wire cutter
  • wire stripper
  • staple gun and staples


Step 1: The Box

My wooden melon box has slats and wide gaps along both sides and the bottom.  Lay the box on its side.  The open top is now the open front of the light box and the former side is now the top.  Cut the corrugated to fit the back and the two ends of the box and staple it in place.  This is to reflect the light and to keep it inside the box where it will help the seedlings. 

Step 2: Preparing the Plywood for the Electricals

Place the plywood on top of the box and square it up.  Hold it securely and mark the gaps between the slats.  This is where you will attach the lampholders that hold the lamps.  The lampholders will extend the lamps inside the box.  

Remove the plywood and place it on your work table.  Draw a line across the middle of the plywood, at about 11".  Assemble a tube to two lampholders and center them between the lines you drew.   Also, center the tube and lampholders between the ends of the box.  Mark the lampholder slot locations.  Mark the tube and lampholders location for the second pair of lines you drew.  Set the tube and lampholders aside and start the screws at the four places you marked for mounting the lampholders.  Remove thelampholders from the tube.  Slip the lampholder unto the screw and just snug the screw to the lampholder.  Don't over tighten or you may crack the lampholder. 


Step 3: The Electrical Part

Secure the ballast to the top of the plywood, making sure not to damage the lampholders in the process.  Follow the wiring diagram on the ballast label to connect the wires to the correct lampholders.  Each pair of lampholders will have yellow wires to one and either red or blue to the other.  

To power the ballast either use the cord you have saved from a dead appliance or snip the receptacle end off an extension cord and strip the leads to about 3/8".  Use wire nuts to connect the plug leads to the black and white leads of the ballast.  Connect the ground wire to the ballast.  Reassemble the tubes to the lampholders and plug the cord in to test the circuit.  If the lamps don't light, unplug the cord and go back over your work, comparing the connections to the wiring diagram shown on the ballast label.  

Step 4: Finishing Up and Using

When the lamps light correctly unplug the cord.  Lower the top with the electricals through the slots in the top of the box.  Plug the cord into a 24 hour timer and set the timer so that the lamps will be lit for 12 hours a day.  Pick off-peak hours.  Cut a piece of white-faced corrugated to fit over the front of the box.

To use the light box, plant your seeds in 6-packs and place them in a flat (no holes in the bottom).  Add about 1/2" of water to the flat and let it sit overnight so the soil can absorb it.  Pour off any extra.  Install the clear plastic cover on the flat.  Place a carton, boards or chunks of foam in the box that are high enough to raise the top of the clear cover to just under the lamps.  Put the flat and cover in  the box, plug in the unit and put the cover over the front of the light box.  

Check your flat every day.  The fluorescent tubes are cool to the touch but they will heat the interior of the miniature greenhouse up to quickly sprout the seeds.  Broccoli can be up in as little as three days.  As your seedlings emerge, they should be uncovered or they may die from damping off disease.  Damping off is the generic term for a number of fungal diseases.  Planting different crops in the same flat is OK but they will probably emerge at different times so be ready to relocate the early ones to another sunny location or uncover everything in the flat and hope the slow developers come up.  

As the seedlings grow, continue to lower the flat so the leaves don't touch the tubes.  While the tubes are not seriously hot, they will damage tender leaves, stunting the plant.  Check the moisture every day.  It is very disappointing to get a good stand of seedlings going and have them die from lack of water. 

 

Step 5: My Alternative Method

For this light box I salvaged my electricals from an old bathroom medicine cabinet that had fluorescents along the sides.  Some of the photos show these mounted to the bottom of the plywood.  Check at your local thrift store or ReStore resale outlet for fixtures.  

This whole project can be enlarges to use a standard 4" fluorescent fixture with two 32 or 40W tubes.  The larger fixture will accommodate 2 flats.   The same principles apply: enclose the lighted area so it is brighter for the plants and keep the seedlings as close to the tubes as possible.
If you use one warm white and one cool white fluorescent bulb instead of two of the same type, you'll get something closer to full spectrum light for your plants.

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