UVA

So I am buying either a 50W or 75W exo terra basking bulb and it says it has uva (I really dont know what it is for if you can explain me) but I was checking my uvb light and it says it has 30% uva so my question here is. Is too much uva bad? Or is it okay if I buy that basking bulb and put them together even though my uvb already has some uva?
 
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