Glow party was night 6 on the Epic two weeks ago. It was quite different from my previous 4 cruises (2 NCL, 2 MSC) where a majority of passengers of all ages wore white and at least dropped by the deck party even if they didn't dance or stay long. The attitude was it was the biggest party of the week. Wearing white wasn't mandatory, but it did look cool under the lights.
On my January Epic cruise, only about 20% of passengers dressed in white, and I got some blank looks on the elevator when I asked who was excited about going. The glow now seems to mean you are given glow sticks to wave around, similar to Carnival's Rock n Glow party. The crowd was pretty young and seemed to be having a good time but we didn't stick around.