More confused yet, Og ?
Kelvin = colour "temperature", but this has nothing to do with power or heat and has little/nothing to do with your blurple. It is more relevant to lighting sources that produce "white" light. The higher the kelvin, the "cooler" the white light and the lower the kelvin, the "warmer" the white light. "Cooler" white lights have more blue spectrum and "warmer" white lights have more "red" spectrum. "Cooler" are known to be better for veg and "warmer" are known to be better for flowering. With a blurple, this is essentially irrelevant because they typically produce lots of red and blue and very little else (hence, "blurple"). Some blurples have separate "veg" and "flower/bloom" switches which turn on separate sets of LEDs to change the colour from more blue to more red. In most (all?) cases these are useless and both switches need to be on all the time to get maximum growth in both veg and bloom.
Regarding lumens and watts: Watts are units of power being sucked from your wall, and lumens is one way to measure actual light energy being produced by the light. MANY people around here say "watts are watts" regardless of the light type. This is misleading, because different types of lights vary considerably in their efficiency. Efficiency is a measure of how much power (watts) are actually being converted to light energy (as opposed to heat). This is often measured in lumens per watt (lm/w). A standard incandescent 200w bulb produces FAR more heat and FAR less light than any of the LEDs discussed here. So the "watts are watts" argument is ridiculous.
Those that are saying you need at least 600 watts must be assuming you want to fill that whole 4x4 area with plants. You said you only have two plants in there. Plenty of folks have grown some decent bud off of 2 plants under a 200w (real watts) blurple. Can you grow better bud off of 2 plants under a 200w COB setup? The consensus is "hell yes!" Why? Because, watt for watt, COB puts out more lumens (and a better spectrum) than a blurple.
By the way, lumens are not a great measure of light output in the context of growing plants. A much better measure is PAR (photosynthetically active radiation) but the PAR data is not readily available for all types of lights, and manufacturers often publish false PAR data. Best to simply choose something that other people have had great results with.
My recommendation is to use that blurple for this grow and see how it goes. Keep the light as close to your plants as you can without causing burn/bleaching (start with manufacturer-recommended distances (12"-18") and work from there). Whatever you get will be smokeable and it will get you high - and you will learn a lot of other very important things along the way. If you are not happy with the results, then look into going with a DIY COB or strip LED setup. If/when you get to that point and you are having trouble deciding what kelvin (colour temp.) to choose, a good "general purpose" (veg + flower) colour temperature is 3500k-4000k (generally, but depends on specific LED brand/type).
