Phase-control-dimmable CFLs: my first impressions

[Travis Evans]

So I went to Lowe's and bought some "dimmable" CFLs and light dimmers to
play around with and fill in another conspicuous gap in my lighting
experience. There seems to have been a lot of complaints of poor
performance, compatibility, and so forth with these, so I wanted to see
for myself how well the current models actually work (or not), having
never had an opportunity to try them before.

Initial results seemed rather disappointing. With one dimmer and a
Sylvania 24-watt spiral, the brightness didn't change much until the
dimmer was well below the halfway point. The lowest setting this
particular dimmer could go was about half brightness (power consumption
around 11-13 watts or so). Later I picked up a different-brand
(Utilitech) 23-watt one, with a similar story, though it did make it
slightly dimmer than the Sylvania was able to achieve. Ordinary
incandescent lamps were much dimmer at the lowest setting, but I still
didn't like the arbitrary minimum level limit designed into this dimmer.

So I found a dimmer with a greater dimming range that would allow me to
find out what the CFLs' lower dimming limit actually is. Both CFLs
exhibited quite an impressive dimming range with this one. They would
dim smoothly all the way down to the point where they started
flickering. I took it even lower, and they reached a point where the
tubing would dimly glow only at the ends and not the middle. That's
probably not so good for them, so I brought it back up again.

At lower brightness levels, I notice a bit of a 60- or 120-Hz flicker
effect, like that of a magnetically-ballasted fluorescent or HID (not
referring to the more erratic "swirling" or "snaking" flickery effect if
I take the dimmer down to an extremely low level, which I avoid).
Anyone happen to know if this is normal, or does it mean that the dimmer
setting is still too low and may be damaging the lamp? However, this
condition doesn't simply appear suddenly at one particular point; it
just becomes gradually more prominent as the lamp is dimmed further.

All in all, the potential dimming range of these seems quite impressive
to me. One problem seems to be that at least some dimmers are built
with a nonadjustable minimum brightness level which, while fine for
incandescents, is apparently still too high for the dimmable CFLs.
Unlike incandescent lamps, these CFLs apparently need *very* low dimmer
settings to actually dim significantly.

Unfortunately, it looks like the Sylvania one just failed after only a
day and will have to be returned. This evening I had it on a dim level
(maybe something like 15-25% brightness, I roughly guesstimate) for an
hour or two. Later when I entered the room, the lamp was not operating,
but the base still felt rather warm. The lamp now will not light at all
in any socket at any brightness setting. The dimmer seems fine; other
lamps still work. This makes me worry if reliability may be an issue
with these, as it sometimes tend to be with CFLs in general. Or could I
have done something wrong like running it too dim even though it seemed
to be doing okay (no excessive flicker or obviously erratic operation)?
But how would I know in the latter case--the packaging offers no special
instructions of any kind. I guess we'll see how long the other
Utilitech one holds up.

 

[Travis Evans]

]

Initial results seemed rather disappointing. With one dimmer and a
Sylvania 24-watt spiral, the brightness didn't change much until the
dimmer was well below the halfway point.

This is normal for most dimmable CFLs. The circuits are designed to
respond to the peak AC input voltage, and that voltage does not
decrease until the dimmer is at it's half-way point.
[...]

Unfortunately, it looks like the Sylvania one just failed after only a
day and will have to be returned. This evening I had it on a dim level
(maybe something like 15-25% brightness, I roughly guesstimate) for an
hour or two. Later when I entered the room, the lamp was not operating,
but the base still felt rather warm. The lamp now will not light at all
in any socket at any brightness setting. The dimmer seems fine; other
lamps still work. This makes me worry if reliability may be an issue
with these, as it sometimes tend to be with CFLs in general. Or could I
have done something wrong like running it too dim even though it seemed
to be doing okay (no excessive flicker or obviously erratic operation)?
But how would I know in the latter case--the packaging offers no special
instructions of any kind. I guess we'll see how long the other
Utilitech one holds up.

The problem is that low cost dimmable CFLs do not have any way to
properly increase the electrode heating current as they are dimmed.
Therefore, as you reduce the arc current, the electrodes become too
cool to support the reqiuired current, and the electrodes start
operating in the sputtering mode.

The two Utilitech CFLs are still working so far, but I have noticed a
slight amount of end blackening that seems to be appearing much sooner
than what seems typical. It looks like I would definitely want to run
these at higher brightness settings as much as possible.

The Utilitech packaging does say not to leave them on the "minimum"
setting "for extended periods", but what bothers me is that they neither
define "minimum setting" (which varies by dimmer--in fact, my model
actually has a *user-adjustable* minimum limit), nor "extended period"
(minutes? hours? days? weeks?).

High quality stand-alone dimming
ballasts have special circuits to heat the electeodes as the lamp
current is decreased.

That would be a much better solution. I wish this were more common.

I might not mind having a unit that plugs into a standard,
non-dimmed socket but has its own dimmer circuitry built in. Maybe even
with an IR remote control (I have a Feit Electric LED "party bulb" that
has a remote for changing colors, etc.) which would make it even more
convenient than an ordinary dimmer. I guess this would raise the
already fairly high price too much for CFLs with integral electronics,
though.