In ,
DerbyDad03 wrote:

On Mar 24, 3:24*pm, (Don Klipstein) wrote:
In ,
DerbyDad03 wrote:

I just bought a 3 pack of Sylvania 15W CFL spot lights for my kitchen
fixture.

I know that CFL's take a little while to reach full brightness, but
these take over 2 minutes! *They'd barely be called a "nightlight"
when they first come on.

* This is a CFL with an outer bulb. *Those generally start dimmer and take
longer to warm up.

* The reason: *The fluorescent tubing gets hotter with the outer bulb
around it. *Fluorescent lamps only work well over a limited temperature
range, so the ones with outer bulbs are designed to work best at the high
temperature that they achieve.

Don,

Thanks for the reply, but your "reason" doesn't explain *why* they
start dimmer or take longer to warm up.

Your reason states 2 facts, both of which I agree with:

1 - The tubes get hotter due to the outer bulb
2 - They are designed to work best at their final operating
temperature

They are also white, they are also made of glass, they also contain
mercury.

All of these facts are true, but they don't explain *why* they take so
long to warm up and acheive maximum output.

If you said something like "If they started brighter and heated up
quicker then the air inside the outer bulb would expand too quickly
and the bulb would explode" *that* would be a reason for the dim start
and the slow warm up.

Is something like that the case?

The problem is that 15 watts only produces about 51 BTU/hour of heat,
minus whatever fraction of the electricity becomes light instead.

It takes a couple of minutes for 40-50 BTU/hour to get the tubing up to
the temperature it works best at. It's not just the tubing - the tubing
won't fully warm up until the outer bulb and the air in it also have an
increase in temperature.

What could be done to speed this up:

1. Have the ballast circuitry provide increased power during warmup.
This will both increase light output and speed up the warmup process.

One problem with this is that the filaments at the ends of the tubing
only work properly in a certain power range, and otherwise wear out
quickly. Another is the cost of such a feature, including detection of
need for increased power, and smoothly reducing the power to normal as the
bulb warms up.

2. Make the tubing of thinner glass and the bulb out of thinner material.
However, that would make them break more easily.

- Don Klipstein )