* When is the last time you replaced your acrylics? You may want to take readings with a UV meter, one with the acrylic on, another with the acrylic off. If there is a difference of 20% or more, replace your acrylic. See the FAQ sections on acrylics and UV meters for more information.
* Have an electrician check your actual incoming voltage. It may be too low and therefore minimizing your lamp's potential.
* Make sure that your tanning unit is properly cooled. If your unit is running too hot, that can reduce the lamp's output down to only 70% of what it should be delivering. Check your fans, clean your unit thoroughly, and change any filters.
* Your old lamps may have been a lot "hotter". Often, customers mistake "heat" for "tan". Have your customers follow the recommended exposure schedule. Have them use a body sticker so they can accurately see the results they get after several sessions.
* If you have done all of these things, and are still getting repeated complaints from several customers, get your invoice number, the batch code off of the lamp, and contact the company that you purchased the lamp from. Or, contact the lamp manufacturer. They will probably want to see a sample of the batch you have for testing.