The LEDs used. If you love the Windex look 24/7, get the Blue version. If you want a nice bright white with a ton of pop, get the Pro. With the pros I still get the super blue, ultra black light rave party look in the morning and night. I just don't prefer that look all the time and with the Blues, there was no way to ever get a good white daylight look that I've used and loved with halides and T5s