This one shows the stealthy DRL mod.
Why not just leave the light on all the time? This car had all LED front lights and burning the hours on the dipped headlight will mean more expensive lamps need replacing eventually, but the T10 re many times cheaper to replace, and many times more accessible to change

Assuming you have now fitted fully LED lamps in the C3 headlight cluster, the 'stealthy DRL' mod will change the side lights (W5W) to ultra bright LEDs that come on with the ignition.
The LED W5W used in the project are similar to those available here (eBay). You are looking for the brightest T10 W5W lamp that isn't any wider than a standard lamp.
This is the lamp in position.
I call it 'stealthy' because it uses the standard reflector and fitting in the headlight. There is nothing to stick on the outside or any holes to drill. Unless you look very closely as shown in the photo, you can't see the DRL until the ignition is on.