How many LED light fixtures to put in 30 by 40 Shop

Depends on the light output of the LED tube. There is no specific code for shop lighting. However, average shop lighting will be in the 500 lumens per square foot range. 1200 X 500=600,000 lumens spread over the whole floor. A lot also depends on the ceiling height, reflectivity of floor and wall surfaces, Windows etc. A 40 watt equivalent LED produces roughly 2,000 lumens at the bulb. Generally speaking, you task light and then background light. In my small 240 sq. ft. shop, I have 8 T8 fluorescent tubes but 1/2 are over tools, about 8 ft. off the floor.