This is what I understand. Not 100% fact.
Any time you make the light output "white-er", the bulb actually has some blue tint.
I purchased aftermarket housings for my Jeep, and they came with purple bulbs that had blue'ish output. I hated them. Went to the autoparts store and looke at different bulbs. The guy recommended some bulbs with a very light blue coating. The output was white. No blue tint. It was much brighter than the bulbs that came with the housings. I then picked up a set with no tint. The light was yellow, but even brighter.
If you want brighter, you cant go with something that adds tint to the bulb.