Hi. Please explain to me why is there Truesight auto darkening welding lenses with many different numbers? for instance you got lens 30319, 30313, 30315 ,, 29371 etc. what is the difference between all of them? and is there a shade/color different? and which is witch? i know there are green filer/color lenses,, red, blue. please help me figure it out. Thank you.