Why are so many new growers choosing blurple LED over HPS/MH?
A combination of sales tactics, and a general lack of understanding of how LEDs actually work. For traditional grow lighting, for the average human, the only quantifiable measure of the lamp is "Watts" ...How many watts does it put out? None actually, Watts are a unit of consumption. A better question would be, how much light do I get for the watts it consumes....which is measurable, but that's another discussion....
Think of a diode like a speaker. A speaker
has a maximum amount of "power" it can handle. The more power provided by an amplifier, the louder the sound.
A LED itself (light emitting diode) works on a similar principal, only the light gets more intense, as the power provided, from the driver increases, until a certain point.
So, we build a fixture with 200x diodes capable of consuming 5w each....
In the eyes of a clever marketer, this makes this a 1000W LED.
However, since the driver is only actually supplying enough power to drive the diodes at 1w each, as an example, it's really only a 200W light....
Inflated, and downright false claims of equivalency, in comparison to HID is how many growers got "burned" by LEDs.
The wrong LEDs, and certainly in many cases, not enough LEDs per fixture, at the level of power they are being provided.
Another factor in the drama, is spectrum capabilities.
Quite often, the banner of "full spectrum" is substantially less than a full spectrum.
Purple light, from reds and blues. Plain old white LEDs have a "Fuller" spectrum alone.
Of course, things get far more in depth, but I generally leave that discussion for those far more advanced than I.