A light bulb used as dome light in a car is just a lazy, poor, weak solution. Along the time is gets burnerd by itself and the glass surface becomes blur that results in a brownish low useless light in the cabin.

You can replace the bulb with a new one but the problem will reappear.

You can also buy an aftermarkes led replacement but what if you don't want to wait?

I will show you how i converted the original dome light lamp into a led bright shiining sun.

(the example is made on a smart 451 but it is adaptable on any car that uses fastoon 4cm bulbs)

Step 1: Led Strips

Go on anyexpress or bangood and but 1-2-3-4-5 meters long 12v led strip, cuttable, with at least 3 leds between each cut point (like shown in the picture).

Prefer the models with led 5050 installed on the strip. Make sure that the led emits white cold light, NOT WARM: your car is not a cemetry.

Step 2: Find a Dissipation Plate

I made one cutting in shape a mint box like the one in the picture. Metal dissipates the heat generated from the leds: during summer it becomes really important!

Step 3: Install and Connect the Led Strips

Take inspiration from the picture but do the best you can tu customize your final result.

cover the edges of the metal plate with black tape to prevent shortcut with the circuit you're gonna build
red wire is positive +
i couldn't solder the negative terminal because the material on the lamp doesn't stick at it at all so i used a screw+bolt and i locker the negative wire by screwing it in place
connect as many strip cuts as you can
respect polarity
don't leave any wire loose
as you can see i minimized the amount of wires by connecting the strip's terminals on both sides of the plate

The attached video may help. Voice is not mine! I'm the one with horrible nails. My friend wanted to explain me the importance of sharing my ideas and was suggesting me to use Instructables; in the meanwhile i was taking a video for my Instructables post. life...

Step 4: Keep the Metal Plate in Place

DON'T USE HOT GLUE: it will detach during the first sunny day in spring!

I used a bi-component epoxy like the one in the picture.

Don't shortcut the components with epoxy: is has a minimal conductivity, even when dry.

Step 5: Final Result

Enjoy your new bright shining car lighting solution.

ON OLD CARS OR BIG DIESEL TRUCKS I HIGHLY RECCOMEND YOU TO INSTALL A VOLTAGE REGULATORE CIRCUIT BEFORE THE 12V LED STRIP, just to prevent demages caused by sudden voltage spikes
before reinstalling the assembly, remember to carefully clean and degreas the glass/plastic transparent/semitransparent protection
the solution can be suitable for plate lights as well but you would need to buy and use waterproof led strips and assemble them to keep the packaging waterproof. i did it on a scooter and it is working since more than a year, during summer and winter, no matter the water that gest splashaed on it.