brand new beds and customers (few)complain not getting red enough?!

just opened a new salon a week ago and some say they are not getting "red" enough. these are brand new beds. even when they get in the 432 12min bed. i have had them try different lotions and found one today that made them red. is it the lamps that are used in the new beds? do they take longer to tan? a friend who is glow in the dark white laid in 20min 28bulb bed and did not notice any difference. what's up? thanks tonya
(new kid on the block)