I'm trying to find an oil leak, and I already had a UV flashlight so I tried shining it around the engine before adding any UV dye, and found that the oil naturally glows yellow (without dye). So my question is, what does the dye do that makes it easier to see the leak more than just the natural yellow glow of the oil? If I add dye, can I tell the difference between the oil with dye in it vs the oil without dye under the UV light? And does it make any difference to use yellow glasses (haven't gotten those yet)?