Constructing Neon Signs: Ideas, Tools, and Techniques
Some years back, I demonstrated simulating the scale “blink” of a firefly: Scale Model Animation 7 – Just for Fun! Smallest Scale Model Animation Ever? https://forum.mrhmag.com/post/scale-model-animation-7-%E2%80%93-just-for-fun-smallest-scale-model-animation-ever-12194756 using an ultraviolet (UV) LED and a tiny drop of phosphorescent paint. You can use a similar approach to get good results building “neon” signs.
Figure 1. Original Firefly Video
The basic idea here is to cut, scratch, etch, or scribe the extent of your neon sign design into clear plastic. I have used both acrylic (plexiglass) and clear styrene. About any clear plastic should work. If you use plastic that yellows with exposure to light (particularly UV light) realize that your sign will yellow too. Any workable thickness does the job. I have successfully used 0.040 styrene and 1/8 thick acrylic to good effect.
The simple signs below were all made with repeated “cuts” with a KNK Zing XY cutter using the “Sure Cuts a Lot” control program. The built in font was used to create the simple outlines and borders. I just repeatedly cut into the plastic with a mild strength cut until I could easily feel the outline consistently around the circumference of the sign.
Next I used acrylic phosphorescent paint colors from Vallejo and AK. Each color was lightly painted into the appropriate, depressed outline, then the excess was quickly wiped off with a damp cloth. If I didn’t get the coverage I wanted, I repeated the process until I was satisfied that the outlines were complete. Use a lint-free cloth, not a tissue or paper towel. You can mix colors as long as you apply one at a time and let each color completely dry. The cuts need to be consistent for good looks. The depth will control the amount of paint collected, and hence the brightness of the “neon.”
Figure 2. Example Fluorescent Acrylic colors
Figure 3. Simple Neon Signs Created with KNK Zing XY Cutter (Blue and Orange Fluorescent Paint)
Figure 4. Multicolor Neon Sign – Green and Orange
My neon window display base was made from a sandwich of 0.20 inch black styrene glued together to leave a trough to hold the sign. Three holes were drilled evenly across the bottom to accept three 3mm UV LEDs (#330MUV9C UV LED from: https://www.surplusgizmos.com/3mm-LED-UV-4000-uW-25mA-ultraviolet_p_1448.html ). These LEDSs are cheap and only 4 milli Watts. As with visible LEDs, very bright, high efficiency UV LEDSs are now commercially available. Do not use very bright UV LEDs! Bright UV LEDs can cause eye damage, and remember you cannot see UV light. Low efficiency UV LEDs will often give off a bluish tint. However, most of the energy radiated cannot be seen. It is a good rule never to stare directly into any UV LED. The good news is that these do not need to be brightly lit to be effective. TheUV LEDs I used are rated to operate with a forward Voltage of 3.5 Volts at 20 ma. But I recommend operating them at 10-14ma or less. My neon sign test stand used for the accompanying pictures used a 9 Volt battery to power 3 UV LEDs wired in parallel through a single 120 Ohm resistor. The actual, measured values for these pictures were: battery 8.1 Volts, resistor 120.5 Ohms, and 13.66 ma per UV LED.
Figure 5. Simple Test Fixture for 3 UV LEDs and Sign Holder
In the figures below, you can see examples where I tried to push this approach a bit. The RCA logo with “His Master’s Voice” graphics was scribed with my KNK Zing cutter (there are several brands on the market). This is much more elaborate than a typical neon graphics sign, but I used it to test the limits of this construction. The cutter software has a picture outline capability that generated the cut lines – pretty amazing. It is clear from this example that you can make scale thickness neon “tubes” for most any scale.
The “HOPE” sign was entirely hand done (can you tell? 
) with a sharpened scribe and my old pen and ink labeling templates from a few lifetimes ago. These are shown in the next figure. Didn’t know I was that ancient… eh.?
Figure 6. More elaborate graphic than typical neon sign and simple, hand scribed sign
In my opinion, the RCA sign is too tall for this approach. The upper end looks good in Figure 6. Bet it looks dimmer in reality. There is a “cure” for larger signs – illuminate the sign from multiple sides. The UV LED set can be positioned from any side: top, bottom, left and right, or even more than one side. I can also be illuminated broadside. If done broadside, try not to shine the UV light directly into the viewers eyes, and remember you can adjust the intensity of the UV LEDs by varying the limiting resistor(s). In the case of the 330MUV9C UV LEDs I used, they are rated for up to 25ma continuous current.
Figure 7. Drawing Templates and Scribe
Summary Notes
You should note that that if you make these signs “window size” (as opposed to the close up pics shown here) these actually look pretty good! You likely noted that the cheap UV LEDs will cast a visible blue glow. This can be minimized by choosing the sign background color, the sign’s distance above the UV LEDs, and the electrical current through the LED(s) carefully. Increasing the resistor value to the UV LEDs will decrease the light output. Get a selection of resistor values (10,000-470 Ohm ¼ Watt – they are cheap), and vary the values starting high and lowering as you watch. This will work for any scale. The material I used for hand scribing was soft, clear styrene. I did not try it on other harder plastics. This technique should also work with “gray smoked” plastic, even colored plastics. Remember that you are “lighting up” the fluorescent paint in whatever trough you create. You can also add “glass joins” with a drop of black paint, placed at critical segments. One can also simulate a neon sign “failing” in whole or in part with Arduino control of one or more UV LEDs connected to the Arduino pin(s) with the appropriate current limiting resistor. A modeler could start with the “campfire” sketch presented in the MRH December 2016 issue, A modeler’s introduction to the Arduino, http://mrhpub.com/2016-12-dec/online/ , to demonstrate the failing neon sign, and adjust the timing. Similarly, a simple blinking sign could also be built.
I hope you find this of interest. As always, appropriate comments and suggestions are always welcome!
Have fun!
Best regards,
Geoff Bunza
