Ginger:One of the most common questions I am asked is how to test
lamps that are not new. It usually means that the person asking the question has just purchased a meter and wants to start monitoring their
lamps in the middle of their life cycle.Here's what you do. Put (if possible) three new
lamps in the top of the sunbed and read the output of the new
lamps and compare that reading to what you got from the old
lamps.For instance, if you got a reading of 25 UV Index units in under the new
lamps and 20 from the old ones, you could estimate that the old
lamps had decreased by 20%. If the old
lamps read 17 or 18, it is time to change them.The reason I came to agree with Michael Stepp, President of Wolff Systems Technology regarding the 70% number, is that I did some "expiriments" and found that it is at 60% of new when customers will start to say something about your
lamps. Thus, if you change them at 70%, you will get MOST of their useable life without customer complaints.Hope this helps.Don