RGB LED Light Pen




You've probably seen the numerous Instructables on how to make a Light Pen, which is used to make light drawings.

The techinque of Light Drawing is to place a camera on a tripod, turn off the flash and set the exposure time to the longest setting possible (or make use of a BULB setting on SLR cameras, which will hold the shutter indefinitely until you press the button again) and when you are in a totally dark room, you wave the pen around in front of the camera as it is exposing.  When you're done, the result is a drawing, of sorts.

Now, in the past the pens are clunky and unprofessional looking (modified flashlights and the like) and only have one color available to them.  So, if you want to draw in a rainbow of colors, you need seven different pens, batteries and LEDs.  That starts to get expensive.

My solution is to use a RGB LED.  They contain a Red, Green and Blue LED inside, using a common negative.  Its basically three LEDs in one.  By controlling the brightness of each primary color, I can make essentially any color, including white.

Step 1: Parts and Tools

For this build you need: 

- A tin or pen-like enclosure
- Three (3) Potentiometers
- Three (3) Knobs
- Two (2) AA batteries
- Rubber Grommet
- Wire
- Solder


- Drill and bits
- File
- Knife
- Hot glue and gun
- Allen keys
- Masking tape
- Ruler
- Pencil

Step 2: Assembling the Pen

I selected some small 200 ohm potentiometers, and the aluminum case from a fancy pen.  My plan is to cut a hole in the back of the case for the LED, and have the color knobs on the front, along with a button to turn the LED on.  One knob for each color, so they can be mixed.  A momentary button opposed to a switch make it easy to draw letters and segmented lines.

Take the masking tape and put a strip on your enclosure where you want to put the holes for knobs and buttons.  Measure and mark them with a pencil.  Using a drill bit that is slightly bigger than your potentiometer, drill your holes where you've marked them.  The potentiometers I am using are tiny ones meant for PCBs, and have a 1/8" diameter shaft.  I happened to have some knobs lying around that fit this size of shaft, so I decided to use them.  Also drill the hole for your button.

If your potentiometers have a nut and a threaded collar, then use that to attach them to the enclosure.  Mine have no nuts or threads, so I had to hot glue them in place.  I did this by putting the knob on the shaft, tightening it in place so that it would hold the potentiometer right up against the metal, and hot glued the pot in place.

For the LED, we need to diffuse it so that the light will be more visible from a non-direct angle.   I did this by roughing the outside with a file, but sandpaper would also work.  I decided I wanted to mount it inside a rubber grommet that would make it more attractive.   I found a rubber grommet that the LED squeeze-fit into.  I measured the inner diameter of the grommet and drilled a hole in the back of the enclosure a little bigger than that hole.  I ended up having to trim some rubber off the grommet with a knife to get it into the hole.  I then squeezed the LED into the grommet so the LED protruded out the opposite side.

Step 3: Wiring

The wiring is quite simple, and I am running the circuit of two AA batteries.  Essentially, the potentiometer is controlling how much of the electricity is going to the LED, and how much is going straight to ground.  The more the pot is turned to the left, the more power is diverted to the negative, and the more its turned to the right, the more power is being directed to the LED.

The schematic is below, and can be wired point-to-point with no PCB required.  The middle pin (the armature) of each pot is connected to the + of each LED, and the other two pins on the pot are connected to the + and - of the battery, respectfully.  The - cathode leg of the LED goes to ground.

Now, I did not have a battery holder that would fit inside my enclosure, so I just connected the wires directly to the batteries, wiring them in series.  Plan to have room for a AA battery holder, that will make life a lot simpler for you.

The button is wired between the + terminal of the battery and the three potentiometers, to make sure that there isn't any electricity available anywhere in the circuit when the button isn't pressed.

Step 4: Light Show!

When you're done, press the button and fiddle with the knobs to see what happens!  You can create pretty much any color in the rainbow by adjusting different levels of red, green and blue.

Set up your camera on a tripod, in a dark room, at night.  The room must be pitch-black or this won't work very well.  Set up the camera, and have someone press the button to begin the exposure.  When the camera starts exposing, draw a picture in the air with the light pen.  If you're on a timer, try counting in your head so you can get an idea of how much time you have left to draw.

Below are a series of pictures showing the rainbow of colors you can do with this pen.

Thanks for reading my Instructable.  If you have any questions don't hesitate to ask.  



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    17 Discussions


    4 years ago on Step 4

    hey does this project use programming in arduino? or was it done just with these components

    1 reply

    7 years ago on Introduction

    Guys for an even simpler version of this idea, download an app for your smartphone such as "Party Light" or even a simple "Paint" app.

    You can the position spots of colour anywhere on your screen, and is perfect for light painting!

    Very simple and effective......

    3 replies

    Reply 6 years ago on Introduction

    Sure... there are 100 apps out there that could work like this. If you like electronics like mattthegamer463, you would find out that an app isn't what he was trying to make or describe.

    I am an electrical engineer.. LED's are one of my favorite things ever. Building something with them is even more fun. Having a little light that you built in your room is like.. way better than still just having a phone in your hand and an object not across the room.

    Self made device > Phone
    Self made device > another phone bought specifically for the purpose of light art (this is a second phone mind you)

    What coding comes down to for this is simple any anyone who knows basic code can write a random color function. I code in C++(Bloodshed and Arduino) and Assembly(Freescale) so... yeah.

    I don't mean to bash you but rather try to explain why I think you're comment is... just... lacking respect for something that deserves it.

    ps: it's PWM! for both your screen and that LED


    Thanks for the defense. You'll notice I didn't comment on this guy's comment originally (2011) because I know he doesn't get it. Glad you like my work.


    Reply 4 years ago on Introduction

    I LOVE L.E.Ds and neither do I understand the meaning of "download an app for your smartphone", the RGB LED Light Pen is SOOOOOO SIMPLE, yet AWESOME and if you make it, then it's something to be proud of...

    Can it be done? Yes. Will I be making one? No.

    It has been done, try Googling. Basically you just need a laser pointer in each of the primary colours (red, green, blue) and a prism to combine the beams into a single beam.


    9 years ago on Introduction

     exactly what im looking for for my light painting. thanx for the tip. definitely gonna try my hands on this one


    9 years ago on Introduction

    First off, very nice job on the enclosure, it looks very professional. However, it seems to me that there's a few things you could do to improve the electronics. First off, it seems that you're running the LEDS directly driven from 2AA batteries. This will only provide 3v max, and the blue LED probably wants a bit more. Secondly, when you've got the pots dialled to their lowest resistance, it's possible you'll overdrive the red LED with too much current.

    I think it would be a good idea to add another AA in series (if it will fit) and then install a small resistor on each LED to provide the correct current to each. This should make the green and blue ones brighter, and the red last longer.

    1 reply

    3 AA batteries won't actually fit inside there, which is why I opted out of using them.  The circuit is quite inefficient.  The red LED is fine with the maximum power available being applied, but it outshines all the other colors entirely when at maximum, and the blue suffers.   I put very little time into designing the circuit, and I would suggest that someone who is building this put a little more time into testing different resistors and getting it more efficient.  Thanks for the comment.


    9 years ago on Introduction

    Very professional looking. Nice job!


    9 years ago on Step 4

    I remember when I first did this with a red laser. I thought that was so cool, but this is even better. I think the best way to do this would be to point the camera at a mirror and stand behind the camera. That way you could control the camera yourself and would not have to write backwards.

    1 reply

    Reply 9 years ago on Step 4

    The thing is that touching the camera, even when on a tripod, will still jiggle it just a little bit, and that can mess up the image.   Fully automating it is the best route.  

    Setting the exposure length to 10 or 15 seconds and setting the timer to take the shot makes it a whole lot easier, I found.  You can just count to 10 or 15 in your head slowly so you know how much time you've got left.


    9 years ago on Step 4

    Hey those pics turned out great! The red scribbles are by far the best.


    9 years ago on Introduction

    I must say, that is very amazing. Nice job on the machining, it is very pro-looking.

    RGB LEDs are so amazing, I wish I had some.