I replaced some 4 foot fluorescent bulbs with cheap ($5 ea from E-bay) LED bulbs. I shopped around and found bulbs that produce 1584 lumens. Although this is less than the old fluorescent ones (2850 initial), the LED lamps are directional and the light goes where it is wanted. The fluorescent lamps and reflectors waste some of their light. Visually the LEDs are at least as bright as the old lamps.
The LED lamps are direct wire, meaning eliminate the ballast. After a few months, they started to strobe (flicker does not describe it). At first they would flash for a few minutes and then stay on, but it got worse and eventually they would be off more than on. It turns out these LED lamps have an electronic driver board to convert the 110 AC to about 72 Volts DC. The driver board can be easily accessed by sliding one end pin assembly off the LED bulb.There are three electrolytic capacitors on the board, and at least one of them was degrading. I purchased 100 of each size from Mouser electronics and replaced all three which solved the problem. It may come back since even the new capacitors are rated for 5,000 hours. The LEDs may last 50,000 hours, but the driver electronics will probably not last that long. Easy fix and cost only about $0.35 to fix each lamp.