What current is drawn by LED mains night light?

On a sunny day (Wed, 23 Sep 2009 14:42:56 -0700) it happened Joerg wrote in :

I just held the scope probe next to it. I cannot uniquely identify any switcher RF, lots of other RF though. Some sawtooth like waveform of few kHz near the the bulb... mV So tried the radio, MW 580 kHz or so. Indeed when switching on there is a strong noise, for about half a second, then a sort of white noise stays, much whiter then the other interference crap. Switcher?

On a sunny day (Wed, 23 Sep 2009 16:05:06 -0700) it happened Joerg wrote in :

Since I have the RGB color strips, I finally, after many experiments, changed the night color to: R 0 G 1 B 21 (on an intensity scale of 0-255). And maybe some moon. That was matched against a night sky, based on the thought that there is little or no red at night, no sun, only star light. Very pleasant. It also works well when an other normal CFL source is on further away, complimenting that spectrum (say moon light).

The optimum, of course, would be to replace the EL with OEM, if it can still be had. As far as using an LED, that depends on a lot of factors, like how much room you have, form factor, and so on.

Good Luck! Rich

Maybe a "loose cannon" switcher? One old trick is (or in some markets was) to dither its frequency so you can fly under the EMC radar screens, get away with much in shields and ferrites.

crap.

Yep. Did that between 1977-1987. Really easy to do. ...Jim Thompson

Martin Brown wrote: [snip]

I have seen some which because of age they are unusable. In those, the electrodes have sputtered enough material against the glass to transform it into an opaque, mirror-like surface (from the inside) which delimits visible emissions to zero.

The same principle is applied with barium getters inside some HIDs.

The ones I've seen were very old, screw-base and of the honey-comb type. It is possible that newer types do not sputter electrode material this badly, particularly types which have coated electrodes, like those from PHILIPS or OSRAM.

crap.

But the federales in most places have caught on to that :-(

"Jon Kirwan" kirjoitti viestissä: snipped-for-privacy@4ax.com...

There is a thread on CPF where someone dissected and photographed failed chinese led under microscope. Photos show that phospors (or epoxy) apparently turns black near die

Link:

-ek

A night light we have at work has dimmed enough so it's pretty useless after a few weeks. See if I can dig out the LED and replace it with something a bit better in quality.

Believe me, the inorganic phosphors do degrade in LEDs from photons of energies 3 eV or a bit less.

Part of the problem may be contamination from other ingredients in the LED.

Light intensity of tens of watts per square centimeter, a couple orders of magnitude more intense than in fluorescent lamps (where phosphor life is usually only 10,000's of hours also), is almost certainly part of this issue.

- Don Klipstein ( snipped-for-privacy@misty.com)

That 250mW seems higher than I expected. The LED would draw only a fraction of that and I hadn't expected the supporting circuitry to need so much power.

I don't know which circuit they use in there but when you take a look at the left circuit in this link you'll see some resistive as well as Vce losses:

I see lots of neons either fade to extreme dimness or start flickering and then gradually become "less on" and "more off" in their flickering as they age. The flickerers eventually go completely out. My experience is that a neon glow lamp indicator is usually in bad shape after less than a decade of use.

- Don Klipstein ( snipped-for-privacy@misty.com)

LED nightlights often have a bridge rectifier and a current limiting capacitor in series with one of the AC leads of the bridge rectifier. In addition, there is usually a series resistor to limit inrush current, and a resistor in parallel with the current limiting capacitor to discharge it so that the prongs of the lightlight cannot cause a shock after unpluging it. My experience is that these two resistors combined often dissipate much more power than the LED does.

- Don Klipstein ( snipped-for-privacy@misty.com)

This is interesting :

"The Not-So-Bright LED Night Light"

Seems there are many different circuits one could use. I hadn't anticipated so many!

Those aren't for mains-powered lights. With batteries you can get even lower. IIRC the lowest useful conversion I got was at around 350mV battery voltage, using an RF JFET. I think it was the BF862. Warning to anyone trying this: Be careful. Sloppy wiring can make that JFET sing like a bird and disturb radio bands. You may not even notice such oscillation because it is able to happily do its intended job at the same time.

Can you name any specific ones that do? I use phosphors of various types and I haven't experienced any that degrade that much (to the point of complete failure for purpose like this.) If you mean degrade in a different sense, then perhaps we are talking cross-purposes.

Are you talking about migration into the phosphor? Or something that has nothing to do with the phosphors used? I'm confused about your meaning here.

I assume you are talking about these high-wattage LED cases? Although I don't have experience with them (or phosphors used in that circumstance), I have two thoughts. (1) The web site was talking about night lights, for gosh sake. (2) If the rare earth phosphor is to degrade, you are talking about dissassociation, aren't you? That is primarily a function of eV, not intensity. Though it may increase the odds of two photons stacking into a dissassociation event, I suppose.

I know you can attempt to 'argue' this, but frankly it goes against many years of practical experiences I've had. I admit I haven't used high wattage LED sources, but I've used xenon flash lamps quite a lot in combination with various phosphors for.. almost 20 years now. These lamps have the highest luminance of any light source you can name excepting perhaps some lasers. Those are serious sources and I've used them in continuous situations for decades without needing to change out the phosphor target. I just don't buy the argument.

Like I said, although I can imagine possibilities, my experience flies in the face of the idea of a mere night light LED using a rare earth phosphor with 3 eV photons completely failing to provide visible light levels for human night vision in 3 months being due to the phosphor itself degrading to that point. I just cannot go there. The stuff has to have been chemically unstable to begin with, or poisoned in some way. There are materials which will quench the effect.

Jon

That's probably the key sentence here. There are threading dislocations, plain old thermal runaway because of surface inconsistencies, contaminations, etc. Considering the price of such lights the manufacturers would probably hump every opportunity to scrape off half a penny by going to a different "distributor". And who knows where the stuff is really coming from. I have heard from people who had plain old jelly-bean opamps and similar chips do weird things. Leakage increases that couldn't be explained, and so on. In most cases they had been bought at, ahem, second tier sources.