D.I.Y. Note :
It will be wise enough never to run any type of COB at HO mode .
(75%-100 % of max power dissipation) .
Yeap,better to forget about any kind of "HO operational mode".
It's counter -productive ,energy-consuming,the COBs shift to cooler CCT ,their service life decreases,cooling needs in power terms are 'way out of line' and many more bad-bad things are waiting ,hidden behind the "HO operating mode" .
The rest :
*High Efficiency Mode -(up to 50% of COB's max power.)
One efficient way of course ,is to run HE mode ,and 'make up ' for the low output ,
by using more units of COBs.Cooling is also somewhat easier as an aspect,as of dealing with lower heat power per COB unit.Light spreading & power distribution also ,are close to optimum.The drivers may be dimmable ,offering greater versatility / power savings in case of seedlings/clones/SOG/SCROG/"MILK s".(Mothers I'd Like to Keep .)
* "Pure HE" -
As before ,but the drivers are not dimmable,having a preset output current.
Thus they operate at high efficiency.Most efficient way .
* High Efficiency Mode & Nominal Mode -(up to 75% of COB's max power)
Another way will be using less units of COBs but more powerful drivers ,running the COBs
at NM mode ...Not as efficient way ,but allows for smaller light fixtures.Thus ,a more preferable way for tighter budgets and /or tighter available spaces.Cooling becomes a serious issue,in such case.Use of optics (reflectors mainly),may prove a real enhancement / aid ,also.
* "Multi HE&NM " .(HE & NM modes / multiple units )
Use of multiple COB units / fixtures ,driven with dimmable high power drivers.
Plenty of units & plenty of available power.
The most 'versatile' & 'powerful' ,but also most expensive way .
(Still not as efficient as a "pure HE". Total efficiency is COB eff. multiplied by PSU eff.
Dimmable drivers have their highest efficiency when operated to their full load or close.
So ,at low currents of HE operating mode ,a dimmable high power driver will 'under-perform' counter-acting the high efficiency of COBs ,thus the total efficiency will be decreased,compared to a pure HE mode system using non-dimmable drivers .)