Lumens is one of the ways to measure the brightness of the light. You need to measure the distance of your garage. For example, if your garage is 10 feet high and 15 feet long, and you place the light fixture 12 feet from the floor, then the light will cover an area of 180 square feet. Good garage lights emit at least 55 lumens per square foot of the area. So in this case, you need to get at least 1130 lumens for your garage.  The good news is that most of the LED lights can emit that much lumens. So, when you get a LED light, you will be able to see the things clearly even if they are far away.