It's my guess that these are lit by an array of large LEDs instead of a more traditional bulb, but I don't have any proof of that.

In my area of the country, it's extremely obvious when they've replaced a bulb with an LED array (something that's becoming more and more common around here). You can see the individual LEDs because they don't have a diffusion lens over them.

I seem to recall several years ago that they were replacing bulbs in some traffic signals around here with brighter ones, and those weren't LEDs, they were just really bright bulbs.

So I don't know if you're seeing one or the other... It could be either...