why do CFL's have a warm-up time, but conventional fluorescent lights don't?

Old-school fluorescent tube lights - T8’s, T12’s, etc. - develop full brightness moments after you turn them on. CFL’s take a few minutes to get there. What’s different that makes this so?

They do. It’s just faster. Plus, ceiling mounted lights turn on a whole bank of them at once, so the “dark” to “light” experience is more dramatic.

CFLs have a smaller ballast than tube fluorescent bulbs and fixtures generally do.

The warmup times for CFL really varies.

I bought two twin packs of GE CFLs years ago. Both with the same model number but slightly different packaging. One of the packs were your typical slow warming up bulbs. The other were nearly full brightness immediately.

They can be built to be bright right away. They just don’t usually do that. And the package labels can be very misleading about how quickly they warm up.

A standard spec for warm up time needs to be established. Manufacturers can choose to get their bulbs certified and then allowed to use the approriate label giving warm up time.

The fast warm up bulbs are generally shorter life then standard (slow) start CFLs and from what I have seen use a little more power vs. lumens provided.

What needs to be warmed up in a CFL? Is it the phosphors, the mercury vapor, or some electronic component?

The cathodes need to heat up to get to full light output.

To ensure covered CFLs don’t overheat the mix of chemicals involve tend to mean this type of CFL has the longest warm up time. Up to 3 minutes in some cases.

For this application start shopping for inexpensive Gen 2 LED light bulbs. They are getting close in cost now and work far better.

The warm-up time is mostly due to the need to vaporize the mercury in the lamp. When there isn’t much mercury vapor, the UV output is low, which means the light output is also low. This is also why Fluorescent lamps work poorly in cold areas.

I’ve noticed the T8 lights in my kitchen (I was kind of angry because it wouldn’t use T12 bulbs like the web site claimed) need a warm up time, though not as dramatic as CFLs. None of the T12s in the basement do, whether they’re on magnetic or electronic ballasts.

Still waiting for the Home Depot to get Cree TW series LEDs in stock…