I personally don't agree with having a green piece of armour having the same defense value as an exotic per say but for your new light level to he increased it is an average of your stats on all equipped items (weapons attack rating, armours defense rating) and also something to so with your class items ghost and artefact. all that will make your light higher as in a video on YouTube there was a character who was level 40. had 216 light level and had thorn and 2 legendary weapons equipped. a rare ghost and all rare armour with an artefact. apparently the highest light level is over 400 now