Sunburn or something else?

I was out in the sun yesterday for about 2 hours - the first time this summer I've been out for that long. My legs developed large, triangular patches on the front of my thighs with splotchy edges, but everywhere else I was exposed is still completely fair and unburned. The redness doesn't itch and doesn't have bumps, but is tender. Is this just usual sunburn that is just showing odd or is it some other condition related to sun sensitivity?