Hmmm. My experience is the opposite. My led UV flashlight charges GITD materials way better than my "white" led flashlights. If a white light is working better, I suspect might just be more powerful.
I've played with GITD materials and single wavelength light sources, and generally only blue and higher wavelengths get them going. I've tried 532nm green lasers and they barely get it going.
Writing on an entire wall or panel of GITD paint with a 405NM violet laser is the most fun.