[giwook]

I don't think it's really helpful (nor possible) to get into this level of specificity.

Generally, just apply sunscreen and limit prolonged sun exposure when possible (particularly when UV index is high).

Avoiding sunburns (i.e. prolonged sun exposure, particularly when skin is unprotected) is probably the main thing to focus on as I believe studies have shown there is a high correlation between getting burnt and developing skin cancer.