Tommy:You have found an anomoly that is almost always true and I can't give you a scientific reason why it happens.We ALWAYS keep the fairer skinned individuals at the same time for the first 3 sessions because they will almost always have problems (if they are going to sunburn) on the THIRD SESSION. In your example, we would have kept them at 5 minutes for the first 3 sessions and then moved them up to 7 minutes on the 4th.I am researching the reasons for this happening but, at present, I can't tell you why it happens. All I know is that it does, as you have found out.What I do know is that there is a very small margin of error between the dose it takes to cause them to sunburn and the dose required to develop a tan.Also, we would only go 4 minutes for the first 200 hours of new
lamps and then to 5 minutes after that. If your
lamps were new, this would also affect the situation.Hope this helps.Don