There are only a handful of ways to get Etheric Light. - Level 34 and 35 Prison of Elders will give one each week, per character - Trials of Osiris; the 6 win and 8 win packages will give one each week, per character. Another one is at the Lighthouse chest, which can be grabbed if you go 9-0 on a card - Possible Nightfall strike reward (so far, I've only seen one Etheric Light as a reward from Nightfall) - Iron Banner, one can be purchased with glimmer by reaching rank 3 and then at rank 5, per character. Note that dismantling an item that has been ascended with Etheric Light does not give you an EL, and reforging a weapon that has been ascended with EL will reset the ascension (weapon goes back to max attack 300/331). Edit: whoops, didn't notice you posted this in your group forum, hehe.