Victor Roberts wrote:
[snip]

The main problem with CFLs is HEAT in the ballast
compartment.

After reading a couple of pages on the electronics contained in the "ballast"
compartment of modern CFLs, I am still stumped at the simplicity of this chinese
small nightlight I have on my webpage:

http://ioannis.virtualcomposer2000.com/spectroscope/collection.html

(photos [41]-[43]).

This nightlight is supposedly 1W, but the electronics are extremely simple
compared to what I've seen for modern CFLs. I haven't measured the light output
of the device to know anything about efficiency, but it looks to me like
replacing the tube's phosphor with a bi or tri-component triphosphor (the
nightlight uses halophosphate phosphors so it's closer to the older "daylight"
color) would push the efficiency to some good levels.

My question is, if such simple electronics can drive this small 1W fluorescent
tube, why are such extravaggant electronics needed for modern CFLs?

On Tue, 15 Apr 2008 17:51:28 +0300, "I.N. Galidakis"
morpheus@olympus.mons> wrote:

Victor Roberts wrote:
[snip]

The main problem with CFLs is HEAT in the ballast
compartment.

After reading a couple of pages on the electronics contained in the
"ballast" compartment of modern CFLs, I am still stumped at the
simplicity of this chinese small nightlight I have on my webpage:

http://ioannis.virtualcomposer2000.com/spectroscope/collection.html

(photos [41]-[43]).

This nightlight is supposedly 1W, but the electronics are extremely
simple compared to what I've seen for modern CFLs. I haven't
measured the light output of the device to know anything about
efficiency, but it looks to me like replacing the tube's phosphor
with a bi or tri-component triphosphor (the nightlight uses
halophosphate phosphors so it's closer to the older "daylight"
color) would push the efficiency to some good levels.

My question is, if such simple electronics can drive this small 1W
fluorescent tube, why are such extravaggant electronics needed for
modern CFLs?

Your night light operates at very low voltage, so all it
needs is a simple series impedance to both start and run the
lamp.

You lamp may also use cold cathodes instead of thermionic
cathodes. Cold cathodes are far less efficient than
thermionic cathodes unless the lamp voltage is well above
100 volts. Efficiency is not an issue with a night light,
but it would be for general lighting.

Also, capacitor ballasts, which are used in cheap fixtures
in the US, generate a lamp current with very high current
crest factor, leading to short lamp life if the lamp uses
thermionic cathodes. The higher the lamp current the higher
the current crest factor. You low power lamp may be able to
survive with the current crest factor generated by your
capacitor ballast, but for a lamp of "normal" power rating,
the current crest factor would kill thermionic cathodes in
short order.

Thanks. I cannot see directly under the fluorescent coating to check if this is
a cold or hot cathode, but I suspect it is a cold cathode. It has three prongs
on each side, with two of them short-circuited.

Victor Roberts wrote:
[snip]

Your night light operates at very low voltage, so all it
needs is a simple series impedance to both start and run the
lamp.

You lamp may also use cold cathodes instead of thermionic
cathodes. Cold cathodes are far less efficient than
thermionic cathodes unless the lamp voltage is well above
100 volts. Efficiency is not an issue with a night light,
but it would be for general lighting.

Also, capacitor ballasts, which are used in cheap fixtures
in the US, generate a lamp current with very high current
crest factor, leading to short lamp life if the lamp uses
thermionic cathodes. The higher the lamp current the higher
the current crest factor. You low power lamp may be able to
survive with the current crest factor generated by your
capacitor ballast, but for a lamp of "normal" power rating,
the current crest factor would kill thermionic cathodes in
short order.

Thanks. I cannot see directly under the fluorescent coating to check if this is
a cold or hot cathode, but I suspect it is a cold cathode. It has three prongs
on each side, with two of them short-circuited.

Indeed, the life time of this mini night-light is attrocious. My mother bought
one and it failed within a week. The one I have on my website is the second one,
which I do not operate, in fear of burning it.

I would guestimate a useful life-time of approximately one-two months on
continuous operation, perhaps less.

Also, capacitor ballasts, which are used in cheap fixtures
in the US, generate a lamp current with very high current
crest factor, leading to short lamp life if the lamp uses
thermionic cathodes. The higher the lamp current the higher

In article <osbc04pc44u8jehjb0fhjmd2ql863209bl@4ax.com>,
Victor Roberts <xxx@lighting-research.com> wrote:

Also, capacitor ballasts, which are used in cheap fixtures
in the US, generate a lamp current with very high current
crest factor, leading to short lamp life if the lamp uses
thermionic cathodes. The higher the lamp current the higher

On a remotely related topic: is this why tube diodes generally
have rather low maximum values for capacitor-input filters?

On 17 Apr 2008 08:13:20 +0100, hcb@fki030.fki.uu.se
(Hans-Christian Becker) wrote:

In article <osbc04pc44u8jehjb0fhjmd2ql863209bl@4ax.com>,
Victor Roberts <xxx@lighting-research.com> wrote:

Also, capacitor ballasts, which are used in cheap fixtures
in the US, generate a lamp current with very high current
crest factor, leading to short lamp life if the lamp uses
thermionic cathodes. The higher the lamp current the higher

On a remotely related topic: is this why tube diodes generally
have rather low maximum values for capacitor-input filters?

Do you mean vacuum tube rectifiers?

In article <8rke041q8knmkd88cur2c6eo7l5euuqk3v@4ax.com>,
Victor Roberts <xxx@lighting-research.com> wrote:
On 17 Apr 2008 08:13:20 +0100, hcb@fki030.fki.uu.se
(Hans-Christian Becker) wrote:

In article <osbc04pc44u8jehjb0fhjmd2ql863209bl@4ax.com>,
Victor Roberts <xxx@lighting-research.com> wrote:

Also, capacitor ballasts, which are used in cheap fixtures
in the US, generate a lamp current with very high current
crest factor, leading to short lamp life if the lamp uses
thermionic cathodes. The higher the lamp current the higher

On a remotely related topic: is this why tube diodes generally
have rather low maximum values for capacitor-input filters?

Do you mean vacuum tube rectifiers?

Yes---I am sorry for the imprecise wording.
As far as I remember the maximum input capacitance for C-input
filters was usually in the order of a few tens of uF.

On 18 Apr 2008 09:20:15 +0100, hcb@fki030.fki.uu.se
(Hans-Christian Becker) wrote:

In article <8rke041q8knmkd88cur2c6eo7l5euuqk3v@4ax.com>,
Victor Roberts <xxx@lighting-research.com> wrote:
On 17 Apr 2008 08:13:20 +0100, hcb@fki030.fki.uu.se
(Hans-Christian Becker) wrote:
On a remotely related topic: is this why tube diodes generally
have rather low maximum values for capacitor-input filters?

Do you mean vacuum tube rectifiers?

Yes---I am sorry for the imprecise wording.
As far as I remember the maximum input capacitance for C-input
filters was usually in the order of a few tens of uF.

It's been a while since I used them, but the maximum
capacitance rating could easily be related to the peak
current rating of the cathode.

In article <va4p045ivh7dte6uq7b6e9ga0ld8gsda5s@4ax.com>,
Victor Roberts <xxx@lighting-research.com> writes:
On 18 Apr 2008 09:20:15 +0100, hcb@fki030.fki.uu.se
(Hans-Christian Becker) wrote:

In article <8rke041q8knmkd88cur2c6eo7l5euuqk3v@4ax.com>,
Victor Roberts <xxx@lighting-research.com> wrote:
On 17 Apr 2008 08:13:20 +0100, hcb@fki030.fki.uu.se
(Hans-Christian Becker) wrote:
On a remotely related topic: is this why tube diodes generally
have rather low maximum values for capacitor-input filters?

Do you mean vacuum tube rectifiers?

Yes---I am sorry for the imprecise wording.
As far as I remember the maximum input capacitance for C-input
filters was usually in the order of a few tens of uF.

It's been a while since I used them, but the maximum
capacitance rating could easily be related to the peak
current rating of the cathode.

There's nothing to sputter the cathode coating in a valve/tube
recitifier, i.e. no positive ions hitting it (if the tube is
properly evacuated), and no electrons during current reversal.
The anode metal gets sputtered, but that's too slow a process
to be significant.

On 21 Apr 2008 14:05:53 GMT, andrew@cucumber.demon.co.uk
(Andrew Gabriel) wrote:

There's nothing to sputter the cathode coating in a valve/tube
recitifier, i.e. no positive ions hitting it (if the tube is
properly evacuated), and no electrons during current reversal.
The anode metal gets sputtered, but that's too slow a process
to be significant.

Good point, but there's a maximum current available from any
thermionic cathode that's a function of its temperature,
surface area and the work function of the cathode surface. I
remember from the past that vacuum tubes die when the
cathode coating has deteriorated to such an extent that the
cathode is no longer able to emit a sufficient number of
electrons per second. So, is it possible that the maximum
available current is not that far below the average current
rating of the tube?