The heart of any tanning system is the measurement of the time it takes to tan with a given set of components and tanning lamps. The performance standard for sunlamp products (21 CFR 1040.20) stating the criteria for the recommended maximum exposure time and the adequacy of the exposure schedule was published on September 6, 1985, and became effective September 8, 1986.
Based on this criteria, the recommended maximum exposure time is computed as the lesser of Te or Tm. Te is equal to four (4) times the MED or minimal erythemal dose, and Tm is equal to four (4) times the MMD or minimal melanogenic dose.
The minimal erythemal dose is the UV radiation dose which would cause a barely discernible pink coloration. By definition, one MED would be the minimum dose necessary to cause a discernable pink coloration after 24 hours.
The minimal melanogenic dose is the UV radiation dose which would cause melanogenis, new melanin biosynthesis, or tanning to occur. By definition, one MMD is the minimum dose necessary to cause a noticeable tan after seven (7) days.
Measurements of Te and Tm are accomplished by applying a weighted factor to the irradiance as measured by a sufficiently accurate spectroradiometer. The irradiance is measured over the UV spectrum in 1 nm intervals for power per unit area. Once measured, the following formula are recommended by the FDA for computing the maximum exposure time, Te, and the maximum exposure time, Tm:
The following is the action spectrum for erythema, indicating the weighted factors applied to the spectroradiometric readings to compute Te:
The following is the action spectrum for melanogenesis, indicating the weighted factors applied to the spectroradiometric readings to compute Tm:
The FDA has recommended in 21 CFR 1040.20 that the exposure schedule on the unit provide for exposures of no more than 0.75 MED (3) three times the first week, and then gradually increasing the exposure over approximately (4) four weeks to a point of maximum tanning at which time maintenance of a tan would be achieved by biweekly or weekly exposures of up to four (4) MEDs or four (4) MMDs, whichever is less.
Finally, tanners are divided into groups by skin type. Exposure schedules should reflect different skin types with different schedules. Skin type I, persons who burn easily and severely, and never tan, should not expose themselves to UV, indoor or outdoor.