The acronym FPS correspond to “sun protection factor” and said structured manner which gives our skin protection product applied.

In general, SPF indicates the number of time that can be exposed without burning the skin to ultraviolet radiation.

The FPS depends on the skin type . That is, in the case of a skin to which, with a given radiation, it takes 10 minutes from time redden (DEM: minimum erythemal dose), if applied SPF 30 could remain 300 minutes the sun without burning; ie SPF 30 will provide 5 hours of protection.

As imaginaréis, the calculation of the FPSdepends on multiple factors, the characteristics of skin, how it is protected (Bronzed) at this time of year, solar radiation, which in turn depends on the latitude, weather conditions and hours of incident or exposition.
The answer is clear: no. If we use the above DEM (10 minutes), with an SPF of 50 we would have 500 minutes exposure, that is, more than 8 hours. However, the calculation is not so simple.
We should note that not all sunscreens 

They are equal and equally protect the skin. We know that products containing SPF basically sunscreens should be absorbed perfectly to provide such protection values. Calculations are arbitrary and depend on many factors, such as the absorption capacity of the skin, its thickness, its intrinsic characteristics and temperature and environmental conditions or contact with water.

One of the factors that should influence the choice of FPS is the skin type , because, lower natural skin pigment, the greater should be the FPS of the product that we use.

Remember what skin type you have to know which product will be most useful for you and for the health of your skin:

According to the Guide Solar Protection , supported by the Ministry of Health and the Spanish Association Against Cancer, according to skin type and UVI (ultraviolet index), these are some useful recommendations:
But you will not fool the calculation of the FPS is unclear. Depending upon the product , it may have been obtained by different values and range from a pharmaceutical company to another depending on the amount of product applied per unit area and the type of light source used, which makes these products are not always comparable.
Another concept that is often linked to sunscreen products is the translation of the English FPS SPF ( sun protection factor ), which measures protection against UVB rays. There is also the PPD ( persistent pigment darkening ), which is the index that measures the ability to produce lasting or immediate skin pigmentation and indicating protection against UVA rays.