Not much! Go for the one with more lumens.
John, would you mind getting all the info you need off that fertilizer thread and letting me know so I can delete it and fix your rep that idiot messed up?
stinkyattic Reviewed by stinkyattic on . Light bulb question Whats the difference? Spiral Compact Fluorescent Light Bulb Medium Base, 24 Watts, 120 Volts, 1500 Lumens Long Life 10,000 Hours, 6500K Daylight Color Tone 5.70" Maximum Overall Length Spiral Compact Fluorescent Light Bulb Medium Base, 20 Watts, 120 Volts, 1250 Lumens Long Life 10,000 Hours, 6500K Daylight Color Tone Rating: 5