Like @legalcanada asked, both COBs and LED strips can be used with great success. I think COBs are best for larger canopies of say 32 s.f. or more, where they can be deployed in groups and position higher from the canopy so that their light can spread and even out across the canopy. COBs used in configurations of a few (1-6) emitters are prone to hotspots and dark spots.
LED strips distribute the light across the canopy much more evenly, reducing or eliminating hotspots and dark areas, even when positioned a few inches from the canopy. They are also much easier to work with in terms of heat mitigation. COBs always need hefty heatsinking and/or active air cooling, which often becomes the most expensive and difficult aspect of a COB system.
-b420