Hi Guru, I’m sorry for such a late response but vacation time happened and am back now.
I have only had the blurple now since last December and the COB for just under 3 months now so hard to determine at this point which one I feel is better.
Also, in a 2 X 2 space gonna have much overlap (especially now that I have them so close together…see pics). I will say that IMO the blurple adds more foliage growth (more bushy) than just white light. This is based upon my observation from using many large 9"-11" CFL’s from 2700K up to 6500K and then adding a, “Kind”, blurple flower light bar and seeing immediate difference in leaf growth (more bushy). It’s why I decided to splurge for a good blurple.
So I’m convinced that blurple adds to the available spectrum given off by so called, “white light” even though I would consider 6500K blue and 2700K yellow/red and probably 5000K would be white I guess but they call em all white.
My COB is 3500K and believe the red in blurple (plus I hang an 11" 2700K) gives me enough far end plus the blurple had IR and UV which may help finish faster.
I’m convinced the best spectrum can be achieved by using both, “white”, and “blurple”, regardless if the, “white”, source is HPS, MH, or LED COB.
Most of the current large Maui (update pics following this post) are grown exclusively under the 175 Watt Cob with partial blurple overlap because had AK-48 taking up most of blurple until just a week or so ago. I use elastomeric paint (best reflective available…better than mylar etc.) so get much side light from reflection in a 2 X 2 space.
The blurple only draws 168 watts and buds grown from directly under (approx 17" from canopy with decent penetration) were very dense and compact but the blurple was four times the price of the cob.
If/when I expand or just need another light kinda looking at QB (quantum boards) next time but will always fly a blurple even if not my main light just because I believe it adds also to resin site production (along with the bushy effect).