my line of work consists of working outdoors allday, i have bought sunblock after sunblock ranging from spf 30-70, none of these have seemed to help. I notice the skin on my arms really bright red, then only that area gets dark brown day after day. (my arms are the only area exposed to the sun, since it is too hot to wear long sleeved clothing) I am naturally light complected......is there a way to lighten this area to my natural color? please help:

I'm afraid the only thing you can do is to try stay out of the sun as much as you can (which isn't really an option). Sunblocks are usually to protect the skin from the harsh UV rays, it doesn't necessarily stop you from tanning.
You could try lightening cremes but then you'll only get tanned again.