I am going to stick my neck out here but its what I believe.
Engineers and national organisations have determined that a good tail light
output is what is given from normal 12 volt incandescent bulbs rated at about
10 watts.
Turn signal lights have been determined to be good at 21 watts.
An exception to this is in bad conditions like fog where much brighter tail
lights make sense.  Its a pity that only a few expensive foreign cars have
them in USA
To use 50 watt bulbs as running tail lights is irresponsible in my opinion,
and could be dangerous by being blinding and distracting.

If your lights seem dim, then:
Clean the glasses, inside and out.
Clean the contacts.
Put in new bulbs of good quality and proper rating.
Make sure that they are getting the proper voltage and if necessary clean
switch contacts and replace dirty connectors.
In other words, correct the problem, dont just deal with the symptoms.

In many european countries, if you use rear red fog lights ( mostly 21 watts)
when it is not foggy, you will be stopped and ordered to pay a fine.

Many american headlight are 35 watts on the dipped beam.  To have tail lights
brighter than headlghts is once again........irresponsible and probably
illegal.
Let common sense prevail !!

Flame away        Steve Cotsford