Build Your Own VBBR
ARCS* Variable Black Body Radiator
By Kevin McCarron, Oak Park & River Forest HS, IL

*Astronomy Resources Connecting Schools, Illinois Mathematics and Science Partnership with Univ. of Chicago Yerkes Observatory

Wooden board approximately 1inch x 6inch x 12inch (scrap is fine)
Approx 3-6 ft AWG18-3 cord with plug (from an old power strip or extension cord)
25W lamp vertical filament
½ inch electrical conduit approximately 4-6 inch
Electrical box (deep) 4inch x 2inch

finished dimmer and bulb in socket

   Electrical socket box “ceiling box”
Socket (keyless)
Dimmer switch
Switch plate cover
4 - Wire nuts
12inch of AWG14 solid black wire
12inch of AWG14 solid white wire
12inch of AWG14 solid green wire
4 - # 6 x ¾ inch wood screws
3/8 inch clamp connector
2 - ½ inch set screw conduit            connectors
Safety goggles

most materials
            Screw driver – Phillips #2
            Screw driver – Slotted #2
            1/8 inch drill bit
            Electrician’s pliers or
Needle nosed pliers and
Wire strippers


1. Don Safety goggles.  Check all cords and wires.  There should be no fraying or cuts in the insulation. 

2. Knock outs (the precut circles on the electrical boxes):  Knock out both ends of the 2inch x 4 inch box and one of the ½ inch knock outs on the socket box. 

remove knockouts socket box knockout


3. Connectors: 
dimmer box and connectors

open knockout
Figure 1

      3a. Set screw connectors: One in one side of the 4 x 2 box and one in the socket box (‘ring’ inside, screw outside). 

Tighten connecting lock nut  
Tighten the living daylights (TLD) out of the connector! 

 connectors and dimmer switch assembled boxes  connectors  conduit  ground wire

      3b.Set the clamp connector in the other end of the 4inch x 2inch box.  Screws should be upright & outside the box. Tighten the living daylights (LD). 

4. Conduit: Connect the two boxes with the conduit between the setscrew connectors.  Tighten the LD out of the setscrews.Kevin tightens the living daylights out of connectors

5. Prepare board: Place the boxes on the board and mark places for 2 screws in each box.  Remove the box and drill holes with 1/8 drill bit.

power cord fed through clamp

6. Green wire & fasten boxes: Cut the green wire to length (about 1 inch longer than the two connected boxes).  Strip ½ inch of the insulation off each end of the green wire.  Turn each end in a loop.  Thread through the two boxes.  Place one box over the pre-drilled holes and put the loop of green wire over one of either screw fastener. Place the open end of the loop so it faces the direction you are turning the screw. Screw the fasteners into the board.   Repeat in the other box and put in remaining screws.
dimmer box with wires connected with wire nuts
7. Power cord: Feed about 8 inch of the cord end through the clamp connector and into the 2in x 4inch electrical box.  (Do not tighten in place yet.) Strip about ¾ inch insulation off all 3 wires.



attach curl of loop in cw direction of screw turn
8. Connect the dimmer:  Take dimmer switch, wire nuts & screws out of package.         8a. Use the wire nut to connect the green wire from the extension cord to the green wire of the dimmer.  Put both stripped ends of the wire side by side and place the wire nut over them.  Screw the wire nut down as tightly as possible.  Test the connection by pulling on the wires while holding the nut. 
8b. Repeat with the black wire from the extension cord and either black wire from the dimmer.
8c. Leave the white cord wire alone for the moment.

9. Attach black & white wires: Strip ¾ inch insulation off the solid, separate white and black 14AWG wires.  Use the wire nuts to connect the black AWG wire to the other black wire on the dimmer.  Use the last wire nut to connect the white AWG wire to the white wire from the extension cord. 
attach dimmer to box
10. Attach socket: Feed the other end of the black and white AWG wires through the conduit into the dimmer box and cut to length (leave approximately 3-4 inch of wire to work with.)  Strip ½ inch of insulation off the end of each wire and turn into a loop.  Hook the black wire loop onto one of the brass screws of the socket (either one).  Hook the white wire up to one of the silver screws.  Tighten the daylights out of the screws.

11. Inspect all wires and connections.  Pull them to be sure they are secure.  Make sure

screw face plate onto dimmer box 
12. Secure the dimmer and socket to the electrical boxes (snugly but not tightly enough to crack the plastic!).  Use the #6 2inch screws to attach the dimmer to the 4inch x 2inch electrical box.  Use the #8 screws to attach the socket to the socket box.  The screws should have come inside the packages.


13. Tighten the clamp connector onto the extension cord so it is only snug.  Don’t over tighten. 

put on dimmer switch completed dimmer and bulb in socket
14. Use the small, #6 screws to attach the switch cover over the dimmer.  Push the dimmer knob over the switch. 

** 15. Check the connections for continuity and safety using multimeter.  (Kevin, Vince, Rich, Elizabeth or Dave will do this for you.)  Be sure there is no continuity between the black and white; black and green; and white and green wires.  Make sure that the white wire is connected to the outside of the base of the lamp socket.  (Using a dimmer, you can’t always tell if the black wire is connected to the base of the socket.) 

16. Insert lamp into socket and plug in cord.  Test dimmer (press for on, clockwise to brighten and counterclockwise to dim.) 

High five lab partner and do the “I’ve Wired a Dimmer” dance.