Warm glow of the LCD panel.
What is this, an arcade for ants?
I saw these at a local Toys R Us, and picked a few up. They were selling for $200 HKD which is about $25 USD. They are SUPER tiny, and yet very cool to actually play with. They feature a single game on each cab, and luckily there is no coin slot, just a player 1 button.  As a bonus the marque does light up, which is why I wanted to do a dark/night picture of the machine.
The games have been modified for what I’d assume is an ARM SOC, and game play is somewhat easier. For anyone looking for the exact arcade expedience, they will be no doubt disappointed as many things like sprite animations are simply lacking in this version.
That said the controls are surprisingly very responsive, and it’s almost a treat to play, except of course that the screen is so incredibly small, the sound is faint, and it’s not hard to have your thumb in the way obscuring things.
It’s a neat novelty item, but it’s no substitute for a nice USB arcade stick & a copy of MAME, or the actual PCB & a JAMMA harness.
I’ve seen somewhere that these use a glob-top SoC, and the ROM actually stores all games, with the machine’s game being selected by a series of jumpers on the board.
I’d be more interested and re-purposing the controls & screen for something more like a Pi Zero.
Yep, all 4 (?) games are built-in, with a 0-ohm resistor to select between them. Easy enough to remove the jumper, and wire all 4 inputs to the joystick so you can select a game by holding the joystick in a direction while flipping the power switch. I too thought of using the screen & case with a pocketbeagle.