Citizen COBs are one of the most economical choice for DIYers. The CLU-1818 series offers unmatched performance for its price.
CLU-1818 is a nominal 50V COB which can operate up to 4.14A max (approximately 250W). Best efficiency is seen below 150W with this chip. This chip offers similar efficiency to a CXB3590 of the same color temperature
Can be mounted directly via handy mounting holes, for solderless option this chip uses Ideal Holder 50-2204-CT
Precut Arctic thermal pads are available for the CLU048 series here
80CRI offers a general spectrum with the red peak centered around 600 nm
Tech specs on the COBs are found on the Citizen datasheet here
Thermal Pads are 0.5mm thick Arctic brand, cut to size from larger sheets. You can read about them here