The top flat surfaces of plant leaves is where light is taken in. If you have really researched different types of beans before you get them you will likely have noticed that different flowering times will be given for more northern regions and different times for more southern regions.
Some seedbanks will just give a range of say 7 to 8 weeks, in fact that is how most do it now but in the past many would specify times for different regions. If you ask them questions about the say 7 to 8 week ranges or whatever time frame they give you will find that is in part because they will be grown under different light conditions, both as in region and wattage. Also if you just research strains themselves you will find that different time periods for the different stages of growth are given for more northerly regions and different time periods will be given for more southern regions.
The closer you are to the equator the more direct the light rays will hit the top of the leaves and the more light they will be able to use, they will be more efficient. The more angles the light rays hit leaves the less efficient they leaves will be.
Two plants with identical genetics and given the exact same degree of needed care will grow and flower and produce different yields if one is say grown in Wisconsin and the other near the equator. That is because the one grown in Wisconsin will receive light rays that are far more angled and will not hit the tops of the leaves as directly as the plant grown near the equator that will receive very direct light rays to the tops of the leaves.
A more efficient usage of light will give faster and more growth in veg time and it will cause plants to flower faster and flower more while in the flowering stage again because the leaves can work more efficiently due to more direct rays of light.
Light from the side is ok to supplement light from above but the more directly above your plants you can have your lights your plants will be better able to use more of the light and use it more efficiently and that means more growth and faster growth and more production.
It is just like growing outdoors, a more direct ray of light hitting the tops of your leaves will give you more growth and faster growth and more production than light rays that are more angled and do not hit the top part of the leaves as directly.