Additional recommendations.
I ordered the lights recommended on this thread off eBay. 2 week delivery time. TEST THEM BEFORE YOU MOUNT THEM. The adhesive tape wanted to come up with the protective strip. Cut your length and peel from the end to the front. These things run a little warm so after mounting the strip to the rail let them run for a while and then press the strip down against the rail between LEDs all the way down the line to help with adherence. You could also use a thin amount of gorilla glue under the strips to help with adherence.

The LED strip kit has a wiring harness on each end. Thank God. Part of one roll was miswired so some selections off the remote were wrong.
It has ONE male connector that is removable so I put it into the other end and found that portion was wired correctly. Gorilla glue the removable male header otherwise it'll come out into the female connector of the wireless remote box when removing.

Mark your connectors! There is a faint molded arrow on the white female connector that the black wire must use and if you plug it in backwards you instantly fry the remote box wireless receiver!

Sync your lights! With both on, turn the brightness of both channels all the way up otherwise you'll get an unequal light pattern.

Use Gorilla glue to secure the wrapped harness end to the rail. I found some spring clamps and used those instead of using the white box as weight.

Lay down a thin layer of Gorilla glue on backside of rail for better velcro adherence.

I am using a Rock Custom Pinball Gameon module. If you choose to go this route you WILL need two female to male extensions . I have emailed him and told him this should be part of the standard kit. Luckily he shipped two trough light mods that had these extensions. The really cool part of this is you dont need to add an external power source not do you have to use those annoying wall warts. Runs right off the power up front and goes off when power in cabinet goes off (the sensor shuts it off when no light is present). Beautiful! Side note: the lights on the right are GI reflection. Shown before, and after with blue/white (equal brightness) and green/white (white turned down). I prefer the white/blue combo.
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Same here and why I made my own. Color and brightness fully adjustable, acts as if it's part of the GI. ~$80 including on/off with the game using the service outlet.

Ordered the LEDs off ebay specified in post #1. Half inch aluminum channel from home depot. Gameon power module. See post #505 for more details.

I use 1/2" velcro. I DO NOT recommend running the entire length of the cabinet. Makes removing them a real chore. These things are stupid light so either put a 3" strip of fuzzy side on each end of the cabinet side wall or (3) 2" left right and middle strips on the side wall. Run the entire backside of the L channel with the prickly stuff to eliminate light potentially coming through the cracks.

On a side note, I really try to keep games GI lighting as factory looking as possible. For example...LOTR, the gameon power module is absolitely brilliant. Stadium lighting goes on and off with the GI. You dont lose any of the mood type feeling when doing it this way. Plus you're using 12v right off the ole service outlet ... no additonal cables run and turns on/off with the game. Not to mention the 12v lights are brighter VS the 6.3 stuff. Same principle when adding LED's. I despise the sharp on/off they give so I use Hergs OCD boards. The cool part is that you can program individual bulbs and allows you to basically buy the same bulbs for the entire machine (unless you're a fan of colored bulbs) and dial em up/down for your liking. Just makes going LED that much easier not to mention you don't have to pay extra for Ghostbusters.

I've seen several remarks made.... something along the lines of "you can spend X amount of dollars on a pin but you wont spend $400?"
I literally despise that line of thinking. First of all I support any business that makes stuff for the community, but for me, I cant stand stadium lighting tied into flashers. It hurts, however I sincerely love adding light to the entire playfield. Spot lights just dont do it for me. But even the "cheap" pin stadiums are what.... $200ish? Luckily I'm a do it yourself type of guy but for someone that's not so "handy" $200 is actually not a bad price. Regardless of his profit margin. $400 is just too damn much money. I used to run a business. I made the choice to make the money in the end not the beginning. What that means is I sold stuff at a lower price but at the end of the quarter I ended up selling more and because of the volume I actually made a little more. I always stuck with that business practice until the day I sold the business. The new owner reverted back to "bleed em for every nickel and the business failed in a year.
This is not a "must have" product so you lose the power to command whatever price you want. Hes a super nice guy, I hope for some reason he sees this and rethinks his business model.

I'm thinking flat bar aluminum 1/8" x 1/2".
These lights are super freaking light weight so you dont need much support. Basically you can create a mount or two where it makes sense to attach on your title. The key here woud be to create a tight cradle for the light bar to sit in (maybe even add soft velcro piece in the cradle). Of course drill a hole in the bottom flat piece to mount onto where ever.
Another cool feature of aluminum being pliable is if needed you can twist the mount the get it "straight" you can. I'm actually out and about right now. I'm going to swing by home depot and see what I can find. I'm actually installing lights on a TAF right now. I do like the idea of NOT using velcro.

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Ready to experiment

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The 1/16" thickness will easily slide between the cabinet and playfield. This is great. No additional shadows or blockage/eye sores.
The plan is to mount under playfield. I believe 2 per side will be sufficient. Now to get some measurements AMD bending going. Need to ensure the base is bent at an angle so the lights run the same angle as the cabinet.

Thought I'd post a pic of my poor mans setup. I prefer to use Gameon power and set the sensor in a gi hole that way the stadium lighting interacts with the gi so it feels like it's supposed to be there. As you can see the before pic is just gawd awful. (Previous owner added warm white leds which suck and are getting replaced with cool white). TAF is kind a night mare to play with stock lighting. The next pic is with full blue/white both @ 100%. Due to TAF having dominate blue on the 3rd pic I turned the brightness down on white and left blue @ 100%. The "chicklet" effect most people complain about is SUPER in your face at the angle the pictures were taken. Normal standing position it's no where near as bad but I plan on adding diffusers.
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Velcro was used.

For the record 1/2" vs 3/4" ... that extra 1/4" is annoying not to mention that's expensive considering for around $13 you get both 1/2" side rails and a can of black paint.
https://www.lowes.com/pd/Steelworks-3-ft-x-0-5-in-Aluminum-Solid-Angle/3053617

Dont disagree, but the flip side of the coin you have complete control over brightness and color. Honestly I "originally" planned on using just white due to all the pinstadium posts showing they annihilated the playfield with flooding color. I played with the brightness, then out of curiosity the color settings and found adding a scooch of a color really helps accent the playfield majority color. Using spot lights is good stuff, but you still end up with dark spots. They might not be ball trafficked areas, but being able to see all of the machine clearly is pretty cool. It does take some getting used too, I wont even lie about that. I also realize it's all personal choice but when I see peoples posts with em on full brightness it makes me think I'm playing a virtual pin, which I very very much dislike Lastly I do have to admit that adding these lights to my LOTR made a world of difference in longevity/playability. I can almost assuredly get to TABA everytime on 3 ball. Owning the machine for 6-7 years so that's huge. I never had that before. Being able to track the ball/balls seriously made a huge difference.

The physical size of those reflectors are something like 1.5"? That rail would have to be the same width .... that's a ton of real estate hanging on the side. Cool thought though.

Thin layer of gorilla glue works wonders. Also great for securing the connector/wires to the channel.

Unplug your added lights. Then either go into the games menu, specifically test the bulb that the Gameon relay sensor relies on or simply use a flashlight. The Gameon will make a SINGLE clicking noise when it receives a light source signal. If it's more than a single click, adjust the gameon sensor position.
Try one of the other gameon power leads.
Ensure the relay sensor is clean.
Ensure your Gameon is being power by the games 12v service port and not a power strip.