A radical is a molecule with an odd number of electrons, and is induced in a variety of ways, including ultra-violet radiation. A sun burn is largely due to radical formation from this radiation. The radical-pair, however, is not simply two radicals.
A radical has an odd number of electrons and can be generated through different means, such as ultra-violet light exposure. Sunburns are mainly caused by the creation of these radicals. In contrast, a radical pair is not just two radicals.