ard at p850ug1.demon.co.uk
Fri May 30 20:57:50 CDT 2008
> On Friday 30 May 2008, Tony Duell wrote:
> > > > After working on a SMPSU (or any power supply for that matter,
> > > > but especially a switcher), I usually power it up to test
> > > > throught a light-bulb. [...] Has saved me from "secondary
> > > > catastrophic failures" on more than one occation.
> > >
> > > And I've heard people talk about banning incandescent bulbs
> > > entirely.
> > Indeed...
> I don't see what the problem is. There are much more efficient methods
> of lighting, than the one that Edison worked a lot on over 100 years
So? I would agree that in many application CFs (or other technologies)
are superior to filamnet lamps. Which is why I generally use said CFs.
But that's not a reason to totally ban filament lamps since there are a
few places where they are still superior.
> In addition to compact fluorescent lamps, you can get LED-based bulbs,
> halogen lamps (which still are effectively incandescent, but a bit
> better), and various gas-discharge lamps.
> > Whele I use compact fluorescent bulbs a lot, there are 4 places where
> > I stick to the old filament lamps :
> > 1) Over my lathe. There is significant 50Hz flicker from compact
> > fluorescents in my experience, I don't want the possible hazard of
> > thinking something is stopped when in fact it's rotating at a
> > multiple of the mains frequency
> I don't think I've ever seen a CF that had a ballast that operated at
> mains frequency. Usually, a switching supply that runs at many kHz.
Actually, earlt ones (perhaps 20 years ago) had an iron-cored choke as
the balanst and ran at mains frequency. I may even still have some of
> Normal fluorescent bulbs, with a "magnetic" ballast instead of
> an "electronic" ballast, though could produce your 50Hz flicker. CF
> bulbs would need do be quite a bit bigger and heavier to have a 50/60Hz
> ballast in them.
However, there can still be mains frequency ripple on the output of the
switching supply. Perhaps I am overcautious here, but I really don't want
to put my hand onto a spinning milling cutter or similar...
> Between that, and the phosphor persistence of the bulb, I don't think
> this could be a real problem. If it is, you could always just run a
> fluorescent bulb off of a DC supply. :)
Which is suppsoeldy bad for them. I can't remember the problem (it's
something to do with uneven 'wear' on the electrodes), but I do recall
that when DC mains were not uncommon there were special swtiches for
fluorescent striplights that reversed the polarity of the supply on ever
other 'on' operation.
> > 2) In my darkroom. CF's have a long afterglow when you turn them off,
> > easily enough to fog film. I want a light source I can turn off
> > instantly
> LED lights turn off much faster than Incandescent bulbs do. Plus, it's
What about white LEDs (which IIRC have phosphors in the plastic package)?
> easy to get/make one that produces red light. :)
I am not talking about the safelight  but about the normal white light
used for seeiong to set things up, etc.
 LED safelights are well-known. And a sodium vapour lamp, sutiably
filtered, can be used with some colour printing papers. Yes, I have one.
> > 3) In my copying stand, where I need a contimuous spectrum of light
> Halogen? There are fairly good spectrum flourescent bulbs available
> these days, but I've not tried to look at them through a prism.
To me, 'halogen' bulbs (assuming you mean tungsten-halogen, and not some
kind of gas discharge lamp) are a subset of 'filament lamps'. And yes,
they are suitable here
> > 4) In my SMPUS current limiter, for obvious electrical reasons.
> Halogen? Maybe a properly engineered RL circuit instead of some
> cobbled-together light-bulb current limiter. :)
I think a tungsten-halogen bulb would eb fine here too.
The point about using a filament lamp for this application is the
non-linear resistance chracteristic. When cold, it has a low resistance
(and effectively no effect on the circuit), buit this reisstance rises to
limit the current if the bulb warms up, e.g. on an overload.
Lamps as current limiters (and even constant-current devices) are
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