34 volts times 1.4 amps gives about 48 watts on the COB.

48 watts times 150 lumens per watt equals 7200 lumens. 7200 lumens is a bit much for a five gallon bucket assuming the bucket is foil/Mylar lined.

Use this 1 amp driver instead.

https://www.amazon.com/LPC-60-1050-1050mA-Single-Output-Switching/dp/B01818B63W

Use this driver if you want dimming.

https://www.digikey.com/product-detail/en/mean-well-usa-inc/XLG-50-AB/1866-5583-ND/9858488

Use this potentiometer if you want to dim the above LED driver.

https://www.amazon.com/HiLetgo-Single-Joint-Potentiometer-Variable-Resistors/dp/B07VJYH29F/ref=sr_1_3?dchild=1&keywords=100k+potentiometer&qid=1600310763&sr=8-3

Don't forget that you'll need either thermal compound or thermal adhesive. Never skip on this.

The heat sink is fine but overkill for this project. It's always better to overkill on the heat sink, though, and in the future if you want to drive the COB harder like up to 100 watts you'll already be set. This COB is a little over 50% efficient so only half the watts has to be dealt with by the heat sink.

When you DIY like this it's really important to get a lux meter if not using a quantum light meter.

https://www.reddit.com/r/HandsOnComplexity/comments/17nxpy/using_a_lux_meter_as_a_plant_light_meter/