How much light does grass need?

We know one thing - plants like grass are very sensitive to light - too little light, too much light, too much blue, not enough far red or UV. Then how do we know how much light to give to optimize growth? 

From what we know, there is currently a growing trend of research, witnessed by the number of inquiries from public and private sectors reported by grow light companies.

There is no simple way of developing a recipe for any particular grass based on a common formula. Right now the research is simply trial and error, but companies and academic organizations are beginning to accumulate databases with their findings.

But how do we know if grass is reacting to certain wavelengths of light - we would have to wait weeks for any sort of physical changes. 

Not really - in research labs, plants are grown in “clean” Growth Chambers, where they are exposed to various test lights. If they are metabolically active (photosynthesis) under the test lights, they will give off the by product O2 . They can then measure this rise in O2 in the chamber very accurately and within a reasonable period of time.

Other than the wavelength of the light, there is one other important factor. A lot of people will think that the brightness of the light in lumens or LUX will make a difference in growing plants. But in fact, both are calibrated for how humans perceive brightness, mostly in green regions, which is mostly irrelevant to grass. Plants like grass care mostly about blue and red wavelengths, and if you have an LED lamp that is registering in those colors only, it will not register as very bright in lumens. But this is misleading as the light will still be quite effective in grass growth.