Great question, Mary! Probably worthy of an article.
Even though the tubes and fixtures can look similar, the difference between what I call a shop light and a grow light is the wavelengths that the bulbs produce.

Grow light bulbs cover a fuller light spectrum, much closer to that of sunlight than shop light bulbs do. The fuller-spectrum grow lights cover all or most light wavelengths, from infrared to near-ultraviolet, which plants need to gather energy.

Shop lights have a much shorter spectrum, usually toward a particular color range measured in units called Kelvin. You've probably heard the terms soft-white, daylight, and cool-white one of those spectrum areas is what shop lights aim toward.

Generally, shop lights are much weaker (less wattage - less power) than grow lights. Meaning they produce fewer photons (particles of light) than grow lights. 

You can think of photons as raindrops. They can "accumulate," so you can run less powerful lights longer and get the same results as a more powerful light that is on for a shorter period. But you can't compensate for the lack of light spectrum that grow lights produce.

The good thing is that microgreens (and any seedling) only really need blue light, which is what 5000K and higher shop lights produce. This is why you can get away without using grow lights. But if you want fruit and flowers, grow lights are the only way.

There is one exception: high kelvin shop lights are not as good at adding red color to leaves, such with some lettuces. The lettuce will be tinged in red but won't be entirely red. Some red microgreens like amaranth, rambo radish, bull's blood beet will still be red, but the red will be more of a greenish-red when compared to the same microgreens grown under grow lights. 

The short of it is you don't need to buy more expensive grow lights if you don't want to and still grow great-looking microgreens.