I bought backup and tail light bulbs for our VWs and Benz here:
www.autolumination.com Tail Light Brake Light Turn Signal LED Bulbs
For the Benz, the backup lighting was brighter. I put the same bulbs in the VW backup sockets, and they're not as bright. Depends on the type of reflector; I guess. Didn't analyze the differences. The LED bulb has the LEDs around the sides; so, if the reflector is mostly reflecting light from its top end, there may not be better light.
In brake light sockets, I experienced 2 problems: 1) radio interference, worse with red bulbs than with white; 2) cruise control ceased to work on the Benz; worked after putting regular bulbs back in; cruise stopped working on the VW and didn't come back with regular bulbs back in place. Of course, you won't experience these problems on a tractor unless you use a radio on it. Cruise on a tractor is a pretty simple device: doesn't depend on the brake light working because there is no brake light.
Think some people on the VW TDI forum have put LEDs in for their head lights. Don't know the details.
Ralph