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Two other areas for additional inquiry:

1) Flicker: does the LED's high-speed flicker play a role in damage to the eye? (Here's an LED viewed in slow motion: https://www.youtube.com/watch?v=3wdljou1M8Q)

2) Spectrum: LEDs can have very uneven spectrums with spikes at particular frequencies (particularly in applications like street lamps that don't use phosphors). This is something an eye in nature would never experience.

Here's a great video showing LEDs strobing compared to other bulb types: https://youtu.be/1IDf16R_eJ0?t=13s




This is why I didn't jump on the spiral CFL bandwagon and why I won't jump on the LED bandwagon for some time to come. Good old-fashioned incandescents may be less efficient to run in summer, but they are heaven to my eyes compared with the crap being sold today. I'll gladly pay for lighting that doesn't make me nauseous or make everything look horrible.


Decent LEDs have very similar spectra and colour reproduction to incandenscent. And everyone on this forum stares at LED or CFL light whenever they look at a computer screen.


Which bothers me less, as it's much darker, contains less blue light with flux or night shift, and doesn't flicker as many bulbs from the hardware store do.


Look for high CRI neutral or warm LED lights.


There's still the flicker and glare, and an unnatural "look". LEDs are not as bad as CFL's, I'll grant you that, but still not as good as an incandescent for the living room or bedroom.


try dimmable, high quality LED's. Osram, Phillips, Sylvania are all good brands to try. stay away from cheap chinese crap.


If the spectrum is good, and there's no flicker, I think this could make sense in the kitchen or hallways. I haven't been that pleased with the LEDs I've seen but they are still better than CFLs and show more promise.

In the living room or especially the bedroom and bathroom, I prefer dimmer lighting with less blue spectrum. My 29W halogen incandescent on the night table doesn't exactly burn through a lot of electricity and has the most pleasing light in my eyes. Until there's a LED that can perfectly match that, I'll stick with that until these bulbs get banned, too.


The LEDs should be in 2 or more groups that each pulse at AC speed but offset by a fraction of the wavelength, that way there is little to no flicker. Or convert to DC and power it that way.


That's WAY too complicated. Just run the power through a high-frequency tank oscillator to convert from 60Hz to a much higher frequency with just a coil and capacitor.

Or, do what I did. Just make the rectifier directly out of LEDs itself - https://www.youtube.com/watch?v=jDnCHyF7o5U And from there you can power your devices with the leftover DC power.

LEDs are seriously far more robust than they were a decade ago.


Not sure this makes sense, when you PWM something like an LED, there is no 'leftover DC power'; the energy unused by the LED each cycle is not wasted.


Yes, there is "leftover DC power" as a diode only allows power in one direction and whatever is left after the LED voltage drop is rectified DC. If I put 12V of LED on a 120V leg, I'll have 108VDC rectified left over after the LEDs take their voltage drop. If no other device uses that power, it just gets dumped out to ground, but it's still unused DC power.

That's not PWM in the video. That's raw mains frequency.


What's the frequency of the 12V AC supply in that video? Is it the same as 110V AC going into the transformer? What is causing the lights to pulse every few seconds?


Yup, same 60hz power mains, it's a simple 10:1 step-down transformer with a resistor and filter cap wall-wart. My camera is recording at 29.97 FPS so you get to watch essentially which sets of diodes on the rectifier are operating on the waveform peak/trough (or would actually see which ones had I had this on an o-scope.) The weird star-trek transporter effect is just the intensity of the lights screwing with the camera + the progressive-scan nature of the camera sensor.

Here's one directly on the mains power. NO CONTROL CIRCUITRY.

https://www.youtube.com/watch?v=AE9QkHmeA-o


You don't want to power LEDs with DC if you want the highest light output. This is because the junction heats up and lowers the efficiency of light output. When LEDs are pulsed at a high enough rate, the junction temperature can stay lower at higher currents. This leads to higher light output.


Fluorescent and gas discharge bulbs also have very spiky spectra. It doesn't seem like the spikiness is a problem in itself.


Fluorescent lamps are also very unpleasant, for the same reason, as are “neon” signs if you look at them up close.

Sodium lamps are much less objectionable because their spectral spikes are at much longer wavelength.


In my opinion neon lamps emit the most pleasant colors to look at.

The only sodium lamps I'm familiar with are high pressure sodium, which emit a garrish orange hue.


To look at, or read under?


Its funny, I replaced 2 spot lights in my kitchen with leds and when I use one certain kitchen device (high speed rotation thing) the leds start flickering visibly.


One or the other doesn't have proper grounding or the cable for power to your appliances is run too close to your cable for lighting (which should be on separate circuits, mind you!)


Different rules here. There is proper grounding, but both the device and leds do not use grounding. Grounding is just for the metal cases, the lamp holder for example.


Proper grounding regardless helps eliminate this.

https://www.youtube.com/watch?v=l6bTSJVLCVI - I used to build fully-functional hydroponics buildings from the foundation-up. Electrical included.


How do you ground a light bulb, and a motor inside a plastic case?

Ground is for safety in AC, when there is a short the ground should take the current away resulting in power loss through the earth that in turn makes the breaker flip. Without grounding the wire that is exposed and touching something will (depending on material etc.) not transfer any current because of too high resistance, then as you touch it it will shock you and then the breaker will go off. (A loss power breaker, not a draw power breaker)

Perhaps you mean the neutral?


"How do you ground a light bulb, and a motor inside a plastic case?"

Same way you complete any other ground - since ground and neutral are literally on the same leg (go look at any installation. You've got TWO wires coming in at the mains, ungrounded.)

So, tell me, how do you ground those ungrounded 240/277V wires??

You don't. Both of them ARE the natural ground dependent upon whether you're at the peak or trough of the waveform. That's kinda how AC works.


Yes the neutral is ground basically.

Where I am from we have installations differently. phase and neutral come in the box, they go through a loss breaker(RCD) and then split up in to multiple breakers. Then those wires go to the socket. Then near the box there is a metal rod in the ground with a wire going to the box, this wire connects to the ground wires coming from sockets. The ground wire, is not connected to anything but things that are not supposed to have any power flowing through.

Yes Neutral is grounded (outside my house, on the main) But when we say we ground things we mean the third connection.

Sorry, didn't know it was so different over there.

edit: Saw the correct name for the "loss breaker" in other post, it is RCD :)

edit: Question, what happens if you hold the neutral to the ground wire there?


Yup, it's different over here. RCD (we call if GFCI here in the USA) tends to be built directly into the outlet, main breakers installed at the box. You guys generally tend to run 240/277V series-ring wire runs, though, yes? We run parallel circuits here.


240V, What we usually do here is run wires to a light point and fan out from there (the light fixture has a small box above it), small rooms can be grouped together by connecting the two boxes. Heavy appliance sockets get separate circuits, and kitchens usually have most circuits. So parallel mostly.


ground and neutral are literally on the same leg (go look at any installation. You've got TWO wires coming in at the mains, ungrounded.)

Forgive my ignorance, I'm no electrical expert, but did you just say that the ground wire is connected to the neutral somewhere in the circuit? Or did I misunderstand you?


That's exactly right. Ground is always tied to neutral in a single-phase 120V installation. Open your breaker box and remove the front panel. You'll see it. http://i.imgur.com/hCY1jV0.png

EDIT: That "always" is assuming the house is modern wiring and not older-style two-prong wiring for the wall outlets. Those systems were just main and neutral at the box and controlled by a fusible link.


Intriguing. I'm from the UK and I believe we do it differently here because I have an RCD on my earth bar in the consumer unit. The RCD detects current on the earth wire and cuts power to the circuit instantly. An earth fault doesn't trigger the circuit breaker, it triggers the RCD. A fault between live and neutral would trigger the circuit breaker.

If I'm understanding you correctly, in the US the ground wire is functionally identical to the neutral due to the bonding. Therefore (this is my own deduction and I'd appreciate being corrected if I'm wrong) you could, in theory, invert the ground and neutral wires in the plug of an electrical appliance and there would be no change in the behaviour or safety of the appliance?


"you could, in theory, invert the ground and neutral wires in the plug of an electrical appliance and there would be no change in the behaviour or safety of the appliance?"

Generally, no. I've seen backwards wiring jobs cause 48-80VAC to run through the casing of microwaves (they usually use the casing as a floating ground.) Any wiring inversion will usually cause some issue somewhere.


This is fascinating, I'm reading lots of resources attempting to understand how this works. Thanks for your responses, I appreciate you taking the time to do that.



That device must be causing the powerline voltage to dip harder than normal (or otherwise screw with the voltage waveform), more than the capacitors in the AC/DC converter for the LED lights are designed to handle. And thus uneven current = flickering light.




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