I bought a couple of the rectangular conversion units shown by vwpieces and used them in my overhead light and as a bulb replacement for the high positioned stop lamp on a Scion XB. They are plenty bright and if you peel away the double sided tape on the back of the square you will find a couple of tiny (probably 1/10W) resistors. They can’t possibly waste that much energy or the resistors would flame up in use. They are similar to the resistors you see next to the LEDs on a SMD strip.
If you are willing to wait for delivery, overseas eBay sellers sell them for less than a dollar each and even have a chip-on-board version out for the same price. Examples:
https://www.ebay.com/itm/48-SMD-LED-T10-1210-3528-5W-12V-White-Light-Car-Interior-Panel-Lights-Dome-Lamp/302590907280?epid=16004064512&hash=item4673d2d390:g:FB4AAOSw4kVZsU3q&vxp=mtr
or the more efficient COB https://www.ebay.com/itm/1pc-New-48-SMD-COB-LED-T10-4W-12V-Light-Car-Interior-Panel-Lights-Dome-Lamp-Bulb/152628342897?hash=item23895bb071:g:5PAAAOSw4A5YnCxG&vxp=mtr