This is a two-sided lamp in the classic London Underground logo (or roundel) style. It's designed to use LED tape of your preferred voltage. The approximate diameter of the shell is 153mm, with the oblong area coming out at 203mm. The cable entry point is to be made by the end user to suit their preferred location (or, to put it another way, make your own 'ole where you want it!).

UPDATE for 2023 - Added a one-piece file for the blue lens for those with Bambulabs printers (and similar). The colours will need to be assigned in your multi-colour slicer.

In the most simple version, the blue oblong is plain, with no writing. But the more complex version incorporates the word "underground" in white. This requires use of the Z-Hop technique to achieve flush white letters that allow light to pass through. Don't worry, it's not difficult - though you may need to practice! I'll tell you more about this later, and link you to a brilliant YouTube video by Chuck Hellebuyck.

The printed parts are as follows:

1) THE SHELL (OR BODY):

This takes the longest time to print of the parts - in my case 18 hours (your mileage may vary). It needs a small amount of buildplate-only support in the recessed areas where the rear lenses will sit. These rear recesses are designed slightly larger than the front ones to allow clearance for any potential "elephant's foot" during printing, and also to eliminate (or, at least, reduce) the need for a perfect clean-up of the support structure before final assembly.

2) THE RED AND WHITE LENSES:

The lamp requires 4 red, and 4 white lenses. Because they are thin, they take little time to print, and require no support.

These will all be held in place in ledged recesses using cyanoacrylate adhesive (CA) on assembly. If you can, print them onto a really smooth buildplate such as glass or steel etc to cut down on visible print lines. If this isn't available on your printer, then I recommend using "ironing" in your slicer of choice.

3) THE BLUE LENSES:

There are two choices for these: A simple plain blue design, or a trickier (but much more satisfying) two-colour lens with writing.

The plain blue lens option is easiest to print. It only requires the STL to be oriented to provide a flat face to the print bed.

The two-colour lens option is designed to print on a single colour machine. It takes advantage of the Z-Hop feature in most slicers. Essentially you print the blue colour part, face down, first. Then you trick your machine into printing the white part straight on top of it. This requires both STLs to be flipped over, face down, and lined up correctly with each other.

If you aren't familiar with the technique, watch this video:
https://www.youtube.com/watch?v=0Sla-vIsvh4
and all should become clear. It might take a few practice runs, but if an idiot like me can do it, anyone can!

I used a 0.8mm Z-Hop height in the print settings. One tip not mentioned in Chuck's video is for machines fitted with bed-levelling. You need disable it! You'll also probably need to locate the print away from the centre of the buildplate so that it doesn't affect the zeroing point at the start of each print stage.

Using Chuck's technique, you create a blue lens with the legend "UNDERGROUND" on it in flush white letters, and the white light only comes through it where it needs to.

ASSEMBLY:

You'll need just under a metre of cool white LED lighting tape. I chose high intensity COB tape, but have since decided this is overkill, and unnecessary. Whilst the light output is undoubtedly amazing, it generates far more heat than the standard tape, and I can envisage this being a potential issue in the future. My advice: Stick with standard LED tape and you won't go wrong.

The shell incorporates tapered areas to provide a continuous bonding surface for the LED strip. However, LED tape backing is notorious (in my experience) for coming unstuck over time, so I recommend securing it using contact adhesive at each end, and at frequent intervals along its length.

Until I obtained my LED tape, I wasn't certain of the best route. So I simply took it around the outside of the shell, and cut it to the nearest segment length. I chose my cable entry hole beside one of the legs, then soldered the cable to the LED tape before I stuck it in place.

With hindsight, I would probably divert the tape to give an extra loop to cover the middle of the lighting area because it appears slightly darker with the tape only around the outside of the shell. I suggest this loop to be the middle of the tape run, and should simply run down and back from the top of the outer shell, around the lower half-circle and return. I've added a rough drawing to illustrate my proposed route. But feel free to experiment!

Once the tape is stuck and tested, all the lenses can be fitted to the shell. You'll want the smoothest faces outwards, and you'll glue them in place using CA glue. The rear lenses may need a little adjusting to fit. I have tried to compensate for elephants foot and/or support leftovers in the lower recesses, but this stuff can vary according to the idiosyncracies of each individual machine.

MATERIALS:

I used PLA+ for all my parts, and printed at 210 degrees C. However, I'm sure other materials will work as well.

Getting the blue right was a little trickier, but I found that eSun do a very nice dark blue PLA+ filament that close enough to the official colour used on the London Underground.

FINAL THOUGHTS:

I hit one small problem with my lamp that shouldn't affect people using standard LED tape: Because I used the high-intensity COB tape, the feed cable is much thicker than normal, and not as flexible. This prevented my lamp from sitting properly on its carefully designed feet! Barely a millimetre or so - and nowhere near enough for the lamp to fall over or anything - but just enough to annoy me!

Because of this, I designed an extra stand that allows a bit of extra room for a thicker cable. You probably won't need this on your lamp, But I've included the STL for those who wish to use it. It can be glued in place or just packed out with felt to make it a friction fit like I did on mine.

Depending on your 3D drawing skills, you could redesign the blue oblong to carry the legend of your choice. All you need to do is fit it within a rectangle of 201.5 mm (don't ask!) and 40mm, with a total thickness of 1.4mm.

Right, I think that's everything covered. So I'll leave you at this point as I have a tube train to catch!