But, just to play devil's advocate, it seems plausible that sunlight might activate some kind of defense mechanism in the eye that protects it from the effects of the higher energy part of the spectrum.
If nothing else, the overall brightness levels would cause your pupil to shrink more in sunlight than under LED lighting.
http://healthland.time.com/2009/08/04/can-cheap-sunglasses-b...
However, the ganglion cells that influence dilation and melatonin happen to be mostly sensitive to blue light (~470 nm), so in theory this would only be a problem for LEDs largely concentrated at even shorter wavelength.
https://en.wikipedia.org/wiki/Intrinsically_photosensitive_r...
(And I own a pair of wavelength-matched laser goggles now, as should you if you're going to do anything at all with a laser and any kind of focusing optics. Carelessly enough handled, even a 5mW pointer beam can pose a real risk. Don't make the same mistake I did!)
Fascinating though it was, I have to say I found the experience with very little to recommend it, not least because it disquiets to realize that the click you've just heard, conducted through the bone and tissue of your head, was produced by a small volume of fluid inside your eyeball suddenly boiling.
[edit] My email's in my profile if you'd prefer not to say publicly, although since a few others upvoted my comment it looks like it's a popular question :)
(The idea there, if you're curious, was to build a light collector with a relatively wide incidence angle that'd focus the beam onto a mostly decapsulated violet LED reverse-biased to act as a photodiode and tied to the base of an NPN transistor, so as to switch a GPIO on my entertainment center Raspberry Pi and use the laser pointer as a kind of remote control. The circuit worked quite well when illuminated, but a ~1mm target is hard to hit from ten feet away, hence the messing about with focusing optics.)
I don't have a detailed characterization of the injury because I'm rather overdue for an optometrist's appointment, but later experiments with the same configuration (and goggles!) showed that, so focused, the beam would deform and start to burn black ABS plastic within a few seconds, and took no perceptible time to burn a hole in a sheet of black construction paper, in both cases producing damage in a radius well under a millimeter - I found that, unless placed precisely in the focal plane, the beam was too widely spread even to raise smoke from the paper. The effect on my retina would therefore have had to be the same sort of closely localized heating, a hypothesis borne out by the effects I observed to result.
Beyond the pain already described (which lasted a good couple of hours), those effects included the click sound I mentioned, which I believe to have been produced by the sudden vaporization of a small volume of aqueous humor adjacent to the retina, and a quite noticeable but thankfully non-foveal bright green floater which did not cease to be perceptible until about a month had gone by. Whether this latter is the result of the injury healing, as I gather such minor retinal injuries often do, or rather of my visual cortex having grown a new filter, I won't know until my next slit-lamp exam.
[1] http://m.ebay.com/itm/Teaching-Powerful-405NM-Blue-N3ioiet-P...
I have worn polycarbonate lenses my whole life, well since infancy. Polycarbonate lenses block UV light. If I go outside without my glasses or sunglasses my eyes hurt, even in winter. I don't know if my eyes are super sensitive or they just aren't used to the UV light and the micro-damage it causes.
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
https://www.youtube.com/watch?v=l6bTSJVLCVI - I used to build fully-functional hydroponics buildings from the foundation-up. Electrical included.
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?
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.
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?
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.
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?
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.
http://ecmweb.com/code-basics/grounding-and-bonding-part-2-3
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?
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.
Here's one directly on the mains power. NO CONTROL CIRCUITRY.
That's not PWM in the video. That's raw mains frequency.
Sodium lamps are much less objectionable because their spectral spikes are at much longer wavelength.
The only sodium lamps I'm familiar with are high pressure sodium, which emit a garrish orange hue.
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.
There are no results which say that our eyes are safer outside.
If you meant: "if we're safer outside then if we've a defense mechanism then we'd be safe "
That's already two "If"s deep and not a reasonable position to take :)