Citizen COBs are one of the most economical choice for DIYers. The CLU-1212 series offers unmatched performance for its price.
CLU-1212 is a nominal 36V COB which can operate up to 2.76A max (approximately 100W). Best efficiency is seen below 50W with this chip.
Can be mounted directly via handy mounting holes, for solderless option this chip uses Ideal Holder 50-2204-CT or BJB for 048 series
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