Process: Wiring Fluorescent Ballasts On The Cheap

My first exposure unit. February 2015 - May 2015. RIP.

My first exposure unit. February 2015 – May 2015. RIP.

A couple weeks ago I broke my first makeshift exposure unit. I was using three 500 watt halogen lights in combination with a compression system (glass, stencil, screen, foam, plywood) held together with clamps. It started with a single halogen at a long distance and I kept adding lights and decreasing the distance. During this last burn the stencil film even melted a bit. Well, the clamps didn’t allow the glass to expand (from the heat) and the whole thing broke. So I’m moving on to a new system and today I’m going to detail wiring fluorescent light ballasts to save a buck.

Fluorescent light fixtures are available in a number of configurations. However, they are often costly and the spacing of bulbs is rarely ideal for exposing screens. My hope is that my move to fluorescents will dramatically decrease exposure time and heat. 

Here are the supplies I picked up for this project from

Ballasts and sockets

Two rapid start electronic ballasts and eight non-shunted medium bi-pin (G13) sockets

Other tools and supplies that I had on hand:

  • Wire strippers
  • Melamine panel board
  • Circular saw (to cut the panel to size)
  • Screwdriver
  • Electric drill with 7/64″ and 1/8″ bits
  • Wire nuts for the electrical connections

The spec sheet for the blacklight indicates that these have a UV wavelength of about 368nm. That should work pretty well for the photopolymerization of emulsion. I think the range to shoot for is between 350nm and 420nm (something like that).

The spec sheet for the fluorescent ballasts indicates that it will work for F18T8, F36T8, F20T12, F34T12, and F40T12. The latter is what I am using. A quick primer on these numbers and letters. Ballasts and bulbs will indicate something like F(X)T(Y) where (X) is the wattage and (Y) is the bulb size in eights of an inch.

T8 = 8/8 = 1 inch diameter
T12 = 12/8 = 1.25 inch diameter

Both T8 and T12 bulbs with medium bi-pins use the same size socket. This socket type is G13. Don’t ask me what those letters and numbers mean.

Shunted Vs. Non-Shunted Sockets

A quick explanation: Shunted usually (but not always) have places for only two wires to go. The contacts for each of the two lamp pins are connected to each other. A non-shunted socket will have connections for four wires and the contacts are not connected to one another. The contacts can be connected by bridging a wire from one side to the other, but we’ll not be doing that here.

There are also differences in instant start, programmable start, and rapid start ballasts. Furthermore, there are electronic and magnetic ballasts. From what I can tell the magnetic ballasts are older and generally require the use of a starter. The ballast I am using here is a Rapid Start Electronic Ballast. It requires non-shunted sockets and does not require a starter. If you buy a different kind of ballast you may need other things and unfortunately the ballast manufacturer probably won’t tell you what you need. I did some combing though a bunch of articles and feel confident that non-shunted is what I want here, but the fact is that even professional electricians seem to get this wrong.


Pencil lines indicate the position for the lamps. A socket lies on the panel with a screw test fitted.

The panel is cut and I’ve marked out the position for lamps. I’m using four bulbs spaced six inches apart. If this isn’t adequate I can add more between at a later date. I came up with these numbers based on other exposure unites I have seen.

A note about these sockets. Generally they aren’t made to be fastened down to a surface like this, so I made sure I had some that I could secure with a screw. The replacement sockets are generally for pre-made fixtures and would slide into a pair of rails.

G13 sockets mounted

Sockets mounted at one end and secured with screws

The first four sockets mounted at one end. The screws I used were just under an inch long and fit in the notches of the sockets. You don’t want your screws to go through your panel. Also, I’m using a sheet of white melamine here only because I had some left over from another project. Plywood would be cheaper, but I didn’t need to go buy a sheet this way. Don’t tighten the screws so tight that you risk breaking the plastic socket.


One bulb is test fitted to make sure they are lined up. To get my sockets lined up I drew a centerline down the panel and measured with a square from the centerline to make sure everything was consistent. For protection of the bulb I simply tore off some ends of the paper sleeve to avoid touching the bulb at this point.

Not shown is the test fit I did even before I mounted the first row of sockets.. These are 48″ bulbs, but the actual measurement is 47.5″. From socket end to socket end was 48″. You could probably afford to be off 1/16″ either way.

Now we’re going to get into some of the technical stuff. Here’s a look at our wiring diagram:

Ballast wiring diagram

Ballast wiring diagrams

The diagram on the top is what is on the fluorescent ballasts. The one on the bottom is what is found on the spec sheet online. The ballast won’t ship with any sort of directions. In fact, the diagram from the online spec sheet is simply black and white. I added these colors in Photoshop for your convenience. You’ll notice all the nice straight lines and right angles. Yours will look nothing like that. If you know what you’re looking at you know that these diagrams in execution are identical, it’s just that on one they reversed the end that the yellow ballast wires go to.

This might look confusing if you never learned wiring diagrams in school, but it’s not a big deal. Here’s what’s important:

On the first side:
Both blue wires go to opposite sides of one socket.
Both red wires go to opposite sides of another socket.

On the second side:
The bottom (or left, depending on where you stand) of one socket will get connected to the bottom (or left) of the other socket. The two wires from each socket will get connected to a yellow wire from the ballast.

The top (or right) of one socket will get connected to the top (or right) of the other socket. These two wires will connect with the remaining yellow wire from the ballast.

Still confused? I’ve got real life photos to make this clearer.

Note: I looked at all the T12 Rapid Start Electronic Ballasts on and they all have essentially the same wiring diagram. Some may appear slightly different in that the yellow wires protrude from the opposite side of the ballast case. I like my ballasts because they were cheapest AND they will accommodate both 18 watt and 36 watt T8 bulbs in addition to the T12 bulbs I am using.

Blue and red wires

A pair of blue and red wires pulled through holes in the panel to be connected to the sockets.

Here we see a pair of blue wires and a pair of red wire waiting to be connected to the sockets. Two holes were drilled through the panel for each socket. The holes need to be big enough for the 18 gauge solid wire from the ballast. I think I used a 1/8 inch drill. If you look in the top third of the photo you can make out the first two sockets that are already completed.

Blue wires connected

Blue wires connected to a socket before being pulled through from the opposite side for a clean look.

Blue wires are connected to one socket before the wires are pulled through to the opposite side for a clean look. The wires simply push into opposite sides of sockets and the socket will grab the wire. There are holes for four wires, two on each side. It doesn’t matter which of the two holes you connect them to so long as each wire is on the opposite side of the notch (where the screw is) from the other wire. I used the outer holes just in case there became a need to modify this socket later and connect the contacts.

Yellow wires pulled through

Yellow wires pulled through to determine available length

On the opposite side I’ve pulled the yellow wires through. They aren’t actually getting connected at this point, I just wanted to see how much wire I had to play with. The yellow wires are longer than the blue or red wires and that’s cool because we’re going to cut them up and splice them together for our connections.

Cutting the yellow wires close to the hole

Cutting the yellow wires close to the hole

Four strands of yellow wire

The ends of two yellow wires have been cut in half and stripped on all ends leaving four strands

With each of the two yellow wires cut, the pair of wires get cut in half and stripped at each end to leave us with four strands of yellow wire.

Yellow strands attached to sockets

Four wire strands attached to two sockets

Each of the four strands gets attached to the sockets. The two on the right need to have the strands pushed through the panel. The one on the left has been completed, and a fourth is out of view.

Yellow connections

The left ballast wires have been connected. The right ballast wires have not.

Here’s what the connection of yellow wires looks like. The left most wire from each socket gets connected to each other and a yellow wire from the ballast. They are both connected with a wire nut. The right most wire from each socket will get connected to each other and the remaining wire from the ballast. It does not matter which ballast wire goes to which socket pair. In this picture the left wires are connected, the right ones are not.

Note: Wire nuts come in different sizes. The package you get should say what combinations of wire sizes it will fit. I picked up a size that fits both two 18AWG and a combination of two 18AWG + one 14AWG. Actually, the connection of the three ground wires has three 14AWG (braided) wires coming together.

Ground wires to ballasts

Ground wires attached to ballast cases

You may recall that the ballast diagram notes that the ballast must be grounded. Here I am running two green wires underneath the screws that connect the ballasts to the panel. Pre-drill mounting holes for the ballasts, but do not go through the panel. Make sure the screws are short enough to not go through the panel. In a commercial application the ballast being secured to a joist or stud would likely be sufficient ground. Since my exposure unit won’t be mounted itself to ground, I took the extra precaution of attaching ground wires. As a further precaution, I scraped away some paint from the ballast tab to make a better connection, but that’s probably not necessary.

Extension cord

Ballasts grounds are connected to power cord

Here are the ground leads connected with a wire nut to the green ground wire in my extension cord. I happened to have an extension cord that was bad on one end that I cut off. It’s can be difficult removing the exterior coating of the extension cord as it isn’t really made for this application. The green wires that lead from the ballasts to the extension cord are simply lengths that I cut from the same extension cord that I am using for my plug. Depending on your power source, you might have a bare ground wire and that’s fine. I wired up the ballast power wires to an old extension cord. You might use a length of Romex that is wired to a switch or outlet or whatever. The wires from the ballast are 18AWG (American Wire Gauge). Your power cord should probably be 14AWG. You might be able to get away with 16AWG (the higher the number, the smaller the diameter of the wire), but I’d really shoot for 14, especially if you’re wiring two or more ballasts.

Note: In the picture above I do not have the black and white power wires from the second ballast wired up yet.

The whole mess of wires

Everything is wired and operational. The wires now have to be tidied up and the power cord fastened securely.

Here is the whole mess wired up. It’s not pretty and isn’t quite done.If you took the panel off an existing fluorescent light fixture, it might not look much prettier. I’ll tie up the wires a bit and won’t count on duct tape to secure my extension cord. You could opt to to fashion another panel to hide this whole mess. You could also use two or three junction boxes for the connections. Whatever route you go, try not go through the bulb side of the panel.

Blacklights on!

Its alive!

I had all the tools and panel supplies on hand. My cost for bulbs, ballasts, and sockets was $59.64 before shipping, which was an additional $12.77, and that includes four extra bulbs for a total of eight. Could you save more by buying this stuff locally? Maybe if you have the right kind of store near you. My local options didn’t carry ballasts and their lamp sockets were three times as expensive. And forget about unfiltered blacklight bulbs.

This will be another makeshift exposure unit to get me by until I know I have time/money/space for a larger vacuum top unit. What I like about this setup is that it is expandable so I can either add another panel side by side or simply add more bulbs to this one if I decide they need to be closer together. In fact, I intend to use this in a future vacuum top unit.

That’s all for today. Once I get a couple screens burned on it I’ll report back with my exposure times.

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