The user sets a timer (or it is set remotely by the salon operator), lies on the bed and pulls down the canopy. The maximum exposure time for most low-pressure beds is 15–20 minutes. Maximum times are set by the manufacturer according to how long it takes to produce four "minimal erythema doses" (MEDs), an upper limit laid down by the FDA. An MED is the amount of UV radiation that will produce erythema (redness of the skin) within a few hours of exposure.