I guess it must be a difference in the way that they are made, because I haven't noticed a prolonged warmup period on any of my CFLs. It takes maybe a second, and they are at full brightness. As far as how dim that they are, that depends on the wattage and color of the bulb. I have a 3000k 150 watt equivalent bulb over my desktop, and a 100 Watt Equivalent 6500k in the kitchen, and the difference is like between night and day. Eventually, I will probably convert all of my CFLs to 6500k. I really like to be able to see what I'm doing.