How well will both hold up against the cold and gravel being kicked up at them?

Under the car? The same. Their both encased in this hard plastic covering.

The LED will be stronger and brighter if the neon tube is punctured at all it wont work but if the plastic casing around the LED breaks the LED's will still work.

neon tubes are inside the same tube as LED's unless the entire outer tube is removed, crushed or shattered it won't break from a stone, they are more prone to breakage from flexing. It depends on what you're looking for. Neon can be as bright as LED and give a very even 360 degree light. LED's have a narrower focus but under the car they just point at the road anyway so it's about the same. If you want to do more than one color so they change go with LED's


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DIY Clear 03+ Headlights