Or ready built and kit ?

I don't have my catalog with me (I'm on vacation this week) but according to what I see on various store sites, the 400x is the "compact type" whereas the 401x is the standard light configuration.

In fact, the 400x serie is called "compact type", but I don't know what that means (except the height: 73 instead of 79 mm)?
Looking at the "English version" on Viessmann site, I see that the 400x serie is in metal. This information was not on the French version I looked before!! That may explain the price difference!(You are right , Mikael)

Thanks to all for your answers

Fred

Hi All

I bought one 400x signal and one 401x .
400x signal are metal instead of plastic, but I must say it is not that obvious to see the difference!
One small difference, however, is in the caps ("Sonnenblenden" ) above the LEDs. In 400x case, caps are not only on the top of the diodes, but also, in part, on each side, (like new Marklin signals, and like the reality, I suppose).
But for my own point of view, I far prefer the 401x, with small cap: It is then possible to see the signal lights everywhere on the layout, without need to put your nose on the track for your eye to be in the right light axis .
Less realistic but more sparkling [:p]!

Fred