Macro Photography Light Source Using Cold Cathode Lights




When shooting using a light tent a low intensity light source is quite useful. The CCFL (cold cathode fluorescent light) found in LCD screens is perfect for this purpose. CCFL and the associated light scattering panels can be found in broken laptop and lcd screens for virtually nothing.
This Instructable shows how to use the a salvaged panel, a DC power source and inverter to create a large, low intensity light.

Some Words Of Warning
This project involves electricity, high voltage and soldering. If you do not feel confident about working with any of these things, do not attempt this project.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Materials

You will need the following materials:
  • Broken LCD panel with a functioning Cold Cathode Fluorescent Light tube
  • DC-AC inverter for your LCD panel and hookup harness
  • DC power source capable of producing at least 12V
  • Soldering Iron
  • Selection of resistors (for a 12V power supply a 70K Ohm and 50K Ohm)
  • Single Pull, Single Throw switch (SPST)
  • Proto/Breadboard
  • Hookup Wire
  • Screwdrivers and other implements of destruction

Step 2: Locate a Broken Lcd Panel

Locate an LCD screen that still faintly lights up, but is otherwise non-functional. If the screen does not light at all, it is most likely suffering from a worn out CCFL or inverter. In this case, you can try to purchase a replacement inverter or tube, but typically this is fairly expensive.

Broken LCD screens can be found on EBay. Look for 15"-17" monitors.

Step 3: Extract the LCD Layer

An LCD panel is made of three layers:
  • LCD - the black colored panel that actually produces images (upper most layer)
  • dispersion layers - there are usually three plastic layers that help disperse the light from the CCFL evenly over the entire panel
  • a reflective panel - the last layer of the panel - the CCFL bulb is usually embeded or attached to this layer. Use extreme care when handling this portion of the screen. The CCFL is very thin tube of glass that is quite delicate. Also, it is filled with mercury vapor which is not so good for you or your brain. Don't break it.

Remove any screws around the frame, and cut any tape from the sides of the frame. Remove any circuit boards from the back of the panel. Extract all three layers from the frame; separate the LCD screen from the other layers. Gently push all the remaining layers back into the frame and reinsert any screws. Set the LCD aside for some other project.

Sometimes the dispersion layers refuse to stay in the frame without the LCD layer in place. A small amount of clear packing tape around the edge of the frame will help solve this problem.

Step 4: Locate a DC-AC Inverter

The CCFL requires a fairly specialized circuit to drive it. LCD inverters can be found on EBay for about $12. Generic inverters will do the job just fine.

If you're salvaging a panel from a broken whole laptop or monitor, locate the small board that the panel plugs directly into.

If possible salvage the wire harness that is made for your inverter. You can remove the stock connector to provide bare wires that are easy to work with. The harness that connects to the DC in side of the inverter is most useful. Unless you have been extremely careless with the panel, the AC harness should still be connected to the CCFL tube.

In theory an inverter should be closely matched to the CCFL it will be used with. This will typically extend the life of the tube and board. This shouldn't be a problem for this type of project, however. As long as the inverter is for a tube of approximately the same size CCFL, it should work just fine.

Step 5: Create a Voltage Divider Circuit

Unfortunately, most manufacturers refuse to release any information regarding their inverters. Some fiddling and testing is usually necessary to determine the input voltages on the inverter before it can be wired up for use. If you are using a complete LCD monitor, simply reassemble it, plug it in and turn it on and skip the rest of this instructable.

From my experimenting I've discovered that many inverters expect 12V+ input to drive the inverter and and around 5V+ to "enable" and set the "dimming" level. Check this generic spec sheet for some guidance: From my testing, the circuits are quite robust and can accept between 4.5 and 7 volts on the enable and dim pins and work properly. Above 7 volts a suspicious whining tends to be emitted.

A 12V DC power source can be easily adapted to power the inverter by using a voltage divider circuit. In a voltage divider circuit, use two resistors to drop the voltage as needed. In this circuit R1 drops the voltage 7V then R2 an additional 5V. Notice that 7V+5V=12V. The schematic below shows the circuit I used to create the voltages I needed to drive my inverter.

In this circuit, C is Ground, A is 12V+, B is 5V+. For an inverter that has enable and and dim pins, connect those to 5V+ to turn the screen on.

Prototype your circuit using a breadboard. Measure the voltage between C and A; it should be 12V+. Measure the Voltage between C and B and it should be 5V+. If you get values within 10-20%, you should be OK.

If you need assistance in choosing resistors for your particular voltage source, check out the Circuit Design Tutor.
Some tips to keep in mind:
  • If the sum of the ratio of the resistors equals the input voltage, your design will be much simpler. For example Vin=12V, ratio of resistors is 50:70 or 5:7 - 5+7=12.
  • Remember you can simply add resistors together in series to create a single resistor (read up on Ohms Law for help here.
  • If your input voltage is 18V, R1 should be 130K Ohm, R2 should be 50K Ohm.

E1: 12V source
A: 12V+
B: 5V+
C: 12V-
R1: 70K Ohm Resistor
R2: 50K Ohm Resistor
K1: SPST switch

Step 6: Test the Circuit

A word of warning here: The inverter creates extremely high voltage output. While it is rather low amperage, it can still do some damage. Don't even think about handling the inverter while it is on. Burns, shocks and maybe even death can occur.

Plug in your voltage divider, power source, inverter and panel and see if everything works. If your inverter is making a high pitched whining sound, it is either damaged or something is receiving too much voltage. Unplug everything quickly and double check your voltages and wiring. If voltages are correct and the whining continues, your inverter is most likely damaged. Find a replacement. Damaged inverters have been known to overheat and start small fires.

Step 7: Enclose the Circuit

Enclose the circuit - I like Ice Breaker Sours Gum boxes. They're super cheap, self sealing, easy to cut and just the right size for small projects.

Step 8: Complete and Use the Light

I salvaged my display from a non-functional laptop, so I had the advantage of having most of the parts I needed at my finger tips. I disassembled the notebook for parts and saved a few bits to complete my light.

I used the following parts to make a more complete light:
  • original screen housing with hinges
  • heat dissipation frame

I mounted the screen backwards on the frame using the existing mount points. This made a handy stand. I only had to counter weight the back to keep the screen from tipping over.

Step 9: Some Shots of the Light in Action

These are some shots that I took using the light. The light was oriented to the right side of the light tent and was the sole source of light for most of the shots.

The shots have been post processed, but only for black/white balance and contrast.

Some Closing Thoughts
I'd like to get a panel with 2 CCFL tubes (top and bottom) and cut a hole in the center and use the panel as a ring flash.

Be the First to Share


    • CNC Contest

      CNC Contest
    • Make it Move

      Make it Move
    • Teacher Contest

      Teacher Contest

    31 Discussions


    10 years ago on Introduction

    Its ok,the "High voltage" is only 50 volts Really,I got shocked by this once and i am not dead.

    9 replies

    Reply 10 years ago on Introduction

    Actually, the output of a CCFL inverter is typically between 120-2000V AC depending on the tube that it is intended to drive. It only takes about 60mA across the heart to induce fibrillation. That means only 60V AC, with sweaty hands (1,000 ohms resistance), is enough to cause some serious problems.

    I have been careless and touched 120V household AC before and fortunately had no ill effects other than that horrible jerk and tingle sensation, but I'd rather not repeat it. The CCFL drivers are pretty safe, but should be handled with the respect and care that any electrical device deserves. It would be a long shot, but they could definitely kill you under the right conditions.

    Check out this for more information regarding electric shock.


    Reply 10 years ago on Introduction to prove my theory,i connected a inverter from a 5 inch screen to a 13 inch,and it lights up perfectly fine Also,somewhere i saw that the voltage for backlights are about 48-49 Volts AC TRUE,It does use a massive amount of electricity to start the bulb,but thats for a very short amount of time,like a few Miliseconds


    Reply 10 years ago on Introduction

    You are indeed correct that there is a voltage spike (strike voltage) when the light is initiated and the voltage does indeed drop during operation. This is due to the fact that a higher voltage is needed to kick start the the ions and produce the initial plasma that releases the photons that you see. Once the plasma is generated, the voltage drops back down.

    The strike and operational voltages have to do with the size and construction of the tube as well as it's intended brightness. A lower voltage source can indeed drive a tube that it was not made for, but not necessarily to the specifications it was designed for. Also, because the gas in the tube heats up and becomes a more efficient conductor, the voltage should drop to extend the life of the inverter and tube. Using an inverter for a tube it was not designed for will not directly damage either, but can shorten their lives.

    Check out this link for a sample of the operational voltages of common CCFL lamps:

    Check out the wikipedia page on CCFLs:

    A quick sample of CCFL voltages reveals the following:
    • Tube for 6.4" display - Strike: 1050V, Operational: 400V
    • Tube for 12.1" display - Strike: 1030V, Operational: 545V
    • Tube for 23" display - Strike: 2010V, Operational: 848V

    Reply 10 years ago on Introduction

    sigh... no i connected my 14 inch CCFL to an inverter for a 6 inch and guess what,it lit up perfectly fine BUT whatever you win

    If the inverter and or ccfl from the laptop is euchred, you could use the inverter and or ccfl assembly from an old flatbed scanner. You could eschew the laptop panel entirely, and use the scanner's platen glass with a piece of paper or something, as a diffuser, although I'm not sure how well that would work.

    6 replies

    The paper would work OK as a diffuser, but the diffuser that is made to work with the light works extremely well. Think about how even the light is on a laptop screen. Good idea to swipe CCFL tubes from flatbed scanners tho; they're a dime a dozen at the thrift stores.

    I agree that the lcd panel diffuser works dandily, I was just thinking that if one didn't have ready access to an old laptop, the paper and glass would be a cheaper substitute.

    Indeed, that would do the job. I think that a couple of white ladies' stockings might work better than the paper too.


    10 years ago on Introduction

    Here's a simpler idea: Instead of removing the backlight, just turn the screen on high brightness and open some blank white file. just a suggestion

    2 replies

    Reply 10 years ago on Introduction

    The LCD panel cuts out about 20-30% of the light. This is about recycling too :)