Build a Colored Shadow Photography Spotlight!

Hello fellow makers,

I recently saw a set of photos on my Instagram feed of photographer Matt Doheny using red, green and blue lights to create amazing colored shadows behind his models and I thought that this would be a great project to attempt.

(Photographs taken by Matt Doheny)

To my surprise after some googling I couldn't find such a spotlight for photography commercially available only some DIY experiments.

A phenomenon occurs when three spotlights, each bearing a primary color - red, blue, and green intersect. The overlapping beams of light merge to form a single, unified beam of white light and the resulting shadows of an object are in the secondary colors yellow, magenta and cyan.

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To build your own you will need the following:

• Access to a 3D printer Amazon - Creality Resin 3D Printer Halot-Mage 8K
• 30cm 2020 Aluminium extrusion Amazon - 11.8inch(300mm) T Slot 2020 Aluminum Extrusion Profile
• Red, green and blue 3W LED diodes Amazon - 3W Led Beads
• 3x 90deg 1-5W LED lenses Amazon - 20mm LED Lens with Holder
• 3x Aluminium LED star base Amazon - LED Heat Sink (2 pin Black) Aluminum
• 4x 2E2ohm 2W+ resistors Amazon - 29 Values 2W 1R-1MR Ω ohm Metal Film Fixed Resistor Kit
• 3x 20x20x6mm heatsinks Amazon - 6x20x20mm Black Aluminum Heatsink
• Thermal double sided adhesive tape Amazon - Thermal Tape, 25m x 20mm x 0.2mm
• USB-C Female socket Amazon - USB 3.1 Type C Connector
• Female camera/tripod mount Amazon - Brass Heat Set Insert fits Standard Tripod Threads 
• 2x M4 Brass inserts Amazon - Heat-Set Threaded Inserts, M4
• 2x 35mm M4 Bolts
• 2x M5 or M6 Bolts depending on your extrusions Amazon - 1080 Pcs Screws Bolts and Nuts Assortment Kit
• Spray paint Amazon - Gloss Caterpillar Yellow

*As an Amazon Associate I receive a small percentage from sales made through provided links at no cost to you, this helps fund future projects.

As with all my projects I use Fusion 360 to plan out and design the components.

The design was built around off the shelf components, starting with the 3W RGB LED's mounted on a star aluminum board that is cooled with 20x20x6mm heatsinks and then fitted to a 20mm 90degree lens.

To get a more defined shadow of each color we want to separate each colored spotlight from each other so I designed the spotlights to mount onto commonly available 2020 aluminum profiles that are mostly found on 3D printers.

A lot of the experiments online simply have the three colored bulbs positioned next to each other but for photography we want a better defined white spotlight where the three spotlights converge so I made it that the centre green spotlight is fixed in position but the red and blue spotlights on the side can be adjusted to achieve the best white spot depending on the distance from your wall.

I printed all of the parts in ABS like resin on my Creality Halot printer but they can also be printed on a normal FDM printer with 0.4mm nozzle.

As this project will be on a shelf when not being used I wanted to make it more visually appealing. The overall appearance of the light reminded me of spotlights used on construction sites so decidedly to paint the main printed components in a Caterpillar yellow and the covers in gunmetal grey.

The only modification that needs to be made to the printed components is to add the two threaded heat inserts into the swivel part of the two side lamp bodies as pictured.

TIP: When using heat inserts with resin printed parts I size the hole so that the it fits snugly around the insert and then smear some CA/super glue around the insert.

The main bodies of the side lights fits over the side rail mounts and are held in place with the two M4 35mm bolts, one on each side.

You will use these bolts to tension the grip for the adjustment so do not overtighten them.

All the pieces simply slide onto the 2020 profile, the two side lights gets held in place by the M5 or M6 bolt depending on your profile and the centre light can either be held in place with a drop of glue or as I originally intended a grub screw through the camera/tripod mount pressing against the profile.

Now onto prepping the RGB LED's.

I start by adding 20mm wide double sided thermal tape to the back of the heatsinks, to make this easier I place the three heatsinks side by side and then take all three at once and then simply trim them. You want to make sure that there are no bubbles or dirt before applying.

Now we will need to limit the current going to our individual LED's, these are all 3 watt diodes that require 600ma per light. The simplest way to limit the current to your LED is to use appropriately sized resistors, using an online Current Limiting Resistor Calculator we can calculate the resistor we need.

Unfortunately this is not a "one size fits all" ordeal, as our red LED has a much lower forward voltage than the blue and green it needs a higher value resistor.

By entering my LED's parameters into the calculator I saw that my red LED requires exactly double the resistance of green and blue, this made it easier because I can buy just one value and just use two resistors on the red LED.

Solder on your resistor to the "+" pad on the LED board and then attach your wire (on the red LED I attached a resistor on the "+" and "-" tabs to double the resistance), I cut the wires about 30cm in length.

Once you've finished soldering you can attach the lenses (I recommend adding a dot of glue just to keep them in place) and then you can attach the front printed cover.

After assembling the diodes I used a 3.7v lithium battery to just test all of the LED's before final assembly.

Our RGB LED's are now ready and we can assemble the spotlight.

We first need to feed the wires of the two side through the front and down the holes in the back into the slots of the 2020 profile. The wires of the side lamps will run in the slots of the 2020 profile and into the centre lamp.

We now need to add the tripod mount insert into it's spot in the centre light, although they are made to just screw in I added some clear all purpose contact adhesive around the thread just to secure it in place.

The wires coming from both of the side lights along with the centre light can now be soldered onto the female USB-C port.

Make sure to double check the polarity of the LED's and the USB port are correct before continuing, LED anode "+" goes to the "V" "+" "VCC" of the USB port and the cathode "-" goes to "G" "-" "GND".

Once soldered and tested you can press the USB-C port through the slot in the centre light enclosure and secure it with the help of some adhesive.

And that's in all of the LED assemblies with the lens covers can be pressed into place and secured with adhesive and then the whole light is ready to get mounted onto a tripod and tested out.

The time has come to test out your creation.

Plug in a USB-C power adapter of 2amps or more then position the light so that the green beam is covering the subject, then adjust the two side lights (red and blue) so that they converge with the green light to create a white spot.

I hope you guys find this Instructable useful and if you have any questions please feel free to leave me a message or comment bellow.

Thank you for taking the time to read through my project and as always..

Happy making!