http://imgur.com/a/WYFG4
You need 2000 Light on your weapon to finish soul attunement.
I'll update these values as I figure out more but so far:
Feeble: 1 Light
Gentle: 4 Light
Brilliant: ?
Blinding: 8 Light
Newborn Star: ?
Tiers:
'No Activity': 0 - 199
'Indisctinct Activity': 200-399
'Faint Activity': 400-599
'Slight Activity': 600-799
'Modest Activity': 800-999
'Distinct Activity': 1000-1199
'Robust Activity': 1200-1399
'Vigorous Activity': 1400-1599
'Intense Activity': 1600-1799
'Extreme Activity': 1800-1999
'Bursting Activity': 2000+ (Complete)