In article ,
"Dave Plowman (News)" writes:
In article ,
charles wrote:
In article ,
Dave Plowman (News) wrote:
In article ,
Andrew Gabriel wrote:
The SL18 was quickly followed by the Thorn 2D lamps - same idea but
with separate reusable control gear. (Thorn eventually sold all
their lamp manufacture to GE, although they retained luminare
design.)

Can you explain to the likes of me how a fluorescent tube with
separate control gear is a CFL?


The C stands for compact. The tube is compact - in comparison with a 4ft
batten fitting.

There were smaller than 4ft tubes around before the 2D. Surely what most
understand as a CFL is a complete unit which can replace a tungsten bulb?

Most people do assume that, but that's not at all what a compact
fluorescent really means. It relates to tubes designed to run at
different (higher) pressure, higher temperature, and higher current
densities than the original fluorescent tubes, which is a way to
make smaller tubes efficient, but it's not only used with smaller
tubes.

Original tubes were designed to run at 40C at an ambient of 25C,
and the gas pressure designed to be optimal at 40C for best
efficiency. (They could be manufactured for other optimum
temperatures, e.g. special tubes made for use in industrial
refrigerators, but each had a fairly tight optimum temperature.)

Compact fluorescents are designed to run at, typically, 100C,
and have much higher loading (Watts/foot of tube length).
The larger temperature difference between switch-on and running
presents a challenge and so does significant variation in the
final temperature. In order to keep the mercury pressure nearer
to optimal over a larger range, they use an amalgam pellet which
absorbs and releases mercury depending on the temperature. This
pellet heating up and releasing mercury is partly the reason for
compact fluorescents having a noticable run-up from a cold start.
Some also rely on a cold limb to regulate the gas pressure (e.g.
all T5HE and T5HO tubes which are also compact fluorescents, the
cold part being the extra tube length behind the electrode at the
labeled end of the tube).

Actually, original fluorescent tubes also have a significant
run-up, but it's much slower, and not such a marked change, so it
was rarely noticed.

Of course it would have made far more sense to stay with the 2D principle
- as it would with LEDs. A separate PS.

Economics of volume production trumps that. Separate parts should
be cheaper, but they aren't when there are orders of magnitude
difference in production quantities.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]