The all new Light Rail 3.5 Intelli Drive with Solid State Advanced Control's fully integrated PCB circuitry will give you the control you are looking for; with an adjustable 0-60 second time delay you can "fine tune" the length of delay at each end of your lamp's travel to meet your garden's ever changing needs.
If your plants are stretching at the ends, simply increase the delay and your plants will all grow at the same rate.
For a rectangular growing area, a linear lamp moving system is preferable. The self propelled Light Rail 3.5 Intelli Drive uses no pulleys, chains or gears. Simply mount the standard 6' track (ships in 2 convenient 3' pieces) to the desired area and place the lamp-moving drive motor onto the track. 3' extensions are available as well to extend it out as much as desired.
The Light Rail 3.5 comes with adjustable switch stops so the lamp travel can be any length you wish. It will easily handle up to 50 pounds of weight.