UVC light (which should be in the QUV-T8) works best, in conjunction with Developer 40 ($6 for 16oz). To get the best/quickest whitening results, it should be done this way by using UVC light with the hydrogen peroxide -- it generates hydroxyl. The hydroxyl radical are an oxidizing agent and whiten the plastic really fast compared to just sunlight, just bleach, or just ozone. It should take about 3-4 hours of exposure for very noticable results.
If you can't fit stuff in the QUV-T8, you can buy ~250nm UVC high power bulbs on Amazon for pretty cheap and just build a box for it. I just bought a 25-watt bulb on Amazon for about $26. You have to be careful though -- some of the bulbs aren't 250nm, and some are shielded which won't do you any good.