Can you quantify "quality of light"

The term "quality of light" is thrown around often, typically referring to equipment. I'm trying to get a better understanding of WHAT is actually meant by quality of light? Is it the source? The modifier? Is the term often used improperly? I watched an hour long video (who's name now escapes me) who described it more about the harshness and softness dictated by modifier size and distance from the subject. In my mind quality of light would mean uniform intensity across the main light pattern and uniform fall off from that pattern.

I ask for many reasons. First, many tout the expensive modifiers like the Mola beauty dishes. A Mola Setti can be had at the tune of $600 vs a 22" Buff for $80. My question is, purely from a LIGHT standpoint, why? Is the light pattern from a Seti nearly 10x better? If it is scientifically designed, I can see the price difference. At the same time, people produce some pretty stunning images with umbrellas so....

Id be more interested in seeing a real life example and explanation using similar images. Perhaps someone with more experience who would likely have some old "junk" lying around oils use a "poor quality of light" setup vs a good quality of light with the same image and settings to illustrate the differences?

don't confuse the word "quality" with "better"

first definition i googled:
quality
noun
1.
an essential or distinctive characteristic, property, or attribute: the chemical qualities of alcohol.

I'd guess not, but if you shoot portraits professionally, it might be better from the standpoint of impressing the client with your great looking equipment? For the same reason that when I go to the head Ref at a v-ball tournament, I have the 70-200 f/2.8 hung on my shoulder & not the unimpressive 85 f/1.8 which is what I'm going to use 99% of the time? ; )

The term "Quality of light", as used in photographic lighting, is a broad and general term used to describe the different characteristics of light and in and of itself when used alone does not describe anything specifically without at least mentioning one or more of the different characteristics of light. You can not quantify it in terms of good or bad; cheap or expensive etc... as you would say to describe a product because photographic lighting is subjective. We can all agree on the different characteristics of light such as hard or soft and long or short etc... and it is these different characteristics that we lump under the term "Quality of light". It is with the placement of light, the direction of light and the use of different light modifiers that we create and alter the different characteristics of light and thus change the "quality of light". Because lighting is so subjective it would just be an opinion as to whether a certain light modifier produced better or worse light than another but a light modifier will produce a certain characteristic of light or "Quality of light". It is up to the photographer to decide which modifier produces the characteristics they find appealing and then to use that modifier in a way that yields the results they desire. Just because a modifier costs $600 and another similar modifier costs $100 does not mean that it produces 6X better light characteristics as that is subjective but it just may be that the materials and construction are better and the product will hopefully last longer and hold up better to daily use.

When I think of quality of light I think of it as light that is appropriate to the subject, having little to do with how it was produced.