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Calculate Sun Protection, Sun Tanning Time

Find out, how long you can stay in the sunlight with which sun protection or which sun protection factor you need for a certain sun tanning time. The calculated value is an approximation, of course you have to take care for yourself not to get sunburned. As protection serve sunscreen, clothes, hat, sunglasses and shade.

Skin type: I: pale II: fair III: light brown IV: olive brown V: brown VI: black
Self-protection time:	minutes
UV Index (UVI):
Sun protection factor (SPF):
Maximum sun tanning time:	minutes hours

Explanations

Skin type
Type I: very light skin, light blonde or red hair, freckles
Type II: light skin, blonde or light brown hair, sometimes freckles
Type III: medium skin, dark blonde or brown hair
Type IV: mediterranean, brown or black hair
Type V: dark skin, black hair
Type VI: dark brown to black skin, black hair

Choosing a skin type sets the self-protection time, this also can be entered manually.

Self-protection time
The maximum amount of time, that the unprotected skin should be exposed to sunlight. An already present tan increases the self-protection time. This doesn't apply to pre-tanning with a sun tanning bed, because those commonly have a different distribution of the UV-radiation (less UV-B) as the sunlight. The WHO advises against the use of sun tanning beds for cosmetic reasons.

UV Index (UVI)
Specifies the intensity of the radiation that causes sunburns. The UV Index is often announced at weather forecasts.
Examples for good weather: spring, noon, Central Europe: 5-7, summer, noon, Southern Europe: 8-10
At 10 a.m. and 4 p.m. daylight saving time (wintertime 9 a.m. and 3 p.m.), the values are about half as high.
Cloudiness decreases this value.
Reflection by snow, sand or water increases this value.
A thin ozone layer (e.g. in Australia) increases this value.
Height above sea level (mountains) increases this value.
8 is the standardized value (summer, noon, Central Europe), not the current one!

Sun protection factor (SPF)
This value tells you, how much longer you can expose yourself to sunlight, when using an according product. Sun protection factor 1 is the self-protection of the skin, a sunscreen with SPF 20 increases the maximum time twentyfold. SPF should refer to UV-A and UV-B. When going into the water, you should use a waterproof sun protection. Please follow the instructions on the label of the product.

Maximum sun tanning time
The maximum time you should expose youself to sunlight without the risk of getting sunburned. This is of course only an approximation, which depends on the correct estimation of the skin type and the UV Index. Staying below this value or using a higher sun protection factor is recommended.
The output is in minutes and the according time in hours.


Formula for the calculation
Maximum sun tanning time = Self-protection time * 8 / UVI * SPF