If you chase the various patents from the Power Mizer you eventually get to this.
Scroll past the ads.

http://www.freepatentsonline.com/3823339.html

Quote
In case of a lamp, its life is lengthened because the filament will evaporate more slowly and retard darkening of the bulb, thereby reducing replacement costs. To get the same lumens as is normal for a lamp of a predetermined wattage and without the rectifier, the rectified lamp must be of a higher nominal wattage.

Greg Fretwell