Whats the point anyway ?

Maybe to appeal to the "greenies"?

There are the glow in the dark switches, it does not use any electricity at all, and the later ones (from the 90s) glow quite bright. The only chemical added in production is Zinc Sulfide (the glow in the dark substance thats mixed into the plastic) which is not polluting (its a common mineral found in nature anyway. The ZnS used in switches and other glow in the dark stuff is of artificial origin, it is waste product from other industries being put to use)

0.1W is very little power, but compare the chemicals used to process the switch components : The Neon is just that, a Glass lamp with 2 Iron electrodes (they dont even use Tungsten there) and Neon/Argon fill. The LEDs being LEDs require all the semiconductor processing and related etching solvents in big quantities, and then some more procesing and chemicals to bond them onto some PCB or PCB substitute that can be assembled into the switch. Which one is environmentally friendly ?

But then you will have trouble marketing it to them.

Greenies on this scale dont use switches anyway, they use motion detectors and the like "energy saving devices". Gotta convince them first that any plain switch at all is good

Greenies on this scale dont use switches anyway, they use motion detectors and the like "energy saving devices". Gotta convince them first that any plain switch at all is good

Oh, but then you have to worry about powering the motion detector.

Even when the resistive LED ballast is so inefficient, the LED's use to be way more efficient than the Ne glow lamps. So at the end you end up with similar brightness.
Mainly when you may go for blue or white, the LED's would be brighter for the same power dissipation.
But there is other thing: The Neons tend to blacken over time, so they have to be replaced after few years.
The LED's in such applications (resistor plus two diodes) are operated at about 1/10'th of their rating (due to the resistor power dissipation), so practically no degradation at all.

The little Neon (without the resistor) is about 20 Lm/W. A good Indicator LED is lets say (and its by a long stretch) 100 Lm/W. So 5 times more efficient. But the ballasting resistor to use with LED is 25 times less efficient, so still all the advantae to the Neon. Would come out even if they used atleast 5 LEDs in series, but why bother with all that ?

Neons go Black because the switch manufacturers like to push them hard. They use it often with as low as 150K resistor on 230V.. quick estimate (230 - 60) / 150K = over 1mA. This brightness level is not needed to see the switch in darkness. They could of used several times higher resistor, so make the Neon last several times longer accordingly.. (i assume for each Electron the chance to kick an Atom out of the electrode is constant, so the blackening speed depend linearly on the number of Electrons so the current)

Motion detectors are Green devices by definition, there is no need to take into account their power use (using Green logic, not actual reasoning)

With LED's you may utilize their lens to make them more efficient. What I know, to make a LED indicator visible and of course safe, you suffice with about 1mA for one half cycle (and zero for the other one; that means about 115mW of power from 230VAC), while the same visibility you would need the 0.5mA to flow in both directions with the Neon, so the same 115mW.

And for the life: The Neons use to be rated for about 1mA as maximum current. By reducing that by factor of two, you just double the life.
But the LED's life depends mainly on the temperature, the rated current of about 15 or 20mA means junction temperatures approaching 100degC (a "3mm" LED with 40degC ambient) and there the rated life is about the same as the Neon rating, so 10k hours or so. But when operated at 1mA, it means more than 10x less temperature rise, so junction temperatures around 46degC for the same 40 degC ambient. That means 54degC lower temperature, so about 45x longer life.
And when the temperature is lower (mostly the case for the switch buttons), the life of Neons remains the same, while the life of LED's gets way longer than the rating.
But the LED needs some extra components. A really minimalistic AC indicator is one resistor and two antiparallel LED's, so one for each current polarity; but that means half the surface brightness. If you wany the maximum brightness, you need an integrated bridge rectifier and/or two diodes (one in series to block the current, other anti-parallel to block the reverse voltage across the LED) extra. And that makes the wiring a bit more complicated (compare to just a single resistor in series with the indicator lamp in the Neon case)

But why not use just one LED instead of 2 antiparallel ones?

The Neon in th switch is in a White Plastic assembly, under the Red transparent button. Most of the light of the Neon is reflected to the button and whatever part goes through. With the LED lets say yo can make all the light directed to the button, its not all that much difference. The purpose here is not to make on/off indicator clearly visible under bright ambient light (which is where lenses of LEDs count), but to spot the switch in darkness, in which case its only plain Lm that count and nothing else. The same Lm flux escaping from 20x20mm button or from 3mm round dot would be equally visible from the far end of the corridor..

Want more life then use a bigger Neon, there are 2mA and 3mA options, you dont have to push to the limits the tiny NE-2... Then you can make it last as long as you want (in the many decades range)

Connecting a LED in reverse polarity to line voltage (that is, in any polarity, as the voltage is AC it will be reverse half of the time) means the LED will go into reverse breakdown in those times. This may damage the LED. (though i seen what looked like ordinary 3mm Red LED used as indicator, with nothing but series resistor on 230V, and it did not appear to be an antiparallel pair in one package either. I guess its breakdown voltage was so low that it did not dissipate much power in reverse)

What If there was a lighted switch bright enough to use as a night light?

Some of the Neon ones are bright enough to use as a nightlight. There is a joke going about this...



Background knowledge required for the joke :

the illuminated switch is a rocker switch, like this :

http://www.ebay.com/itm/KCD4-DPST-4Pin-2-Position-On-Off-Rocker-Switch-Red-Light-AC-15A-250V-20A-125V-/321513601052

It comes assembled into a frame with faceplate, so ready to be installed as a wall switch. It comes in 2 types : The double pole (4 terminals) on/off switch with Neon on/off indicator, or with added return spring inside that makes it a push switch, and wired so the Neon is lighting all the time (in series with the device the switch controls) and is shorted out when pushing the switch

The double pole on/off is used to control water heaters among other stuff, in which case it is located in the corridor near the bathroom



The joke itself, in short, goes about switching on that switch in the corridor to use as an energy saving nightlight

The joke itself, in short, goes about switching on that switch in the corridor to use as an energy saving nightlight

It's the switch for the "eco" people!

But why not use just one LED instead of 2 antiparallel ones?

LED has to be forward biased in order to emit any light.
When in reverse it does not conduct (after all it is a diode), but the voltage should not exceed 5V otherwise the LED will start to degrade.
So you need a rectifier, when operating on AC input.
The problem with the degradation is, it does not need any current for that, so even a reverse leakage of a single rectifier diode may be too much.
So you need one parallel diode extra in reverse, to prevent any voltage buildup.
And the thing is, if you use another LED in that role, you may skip the series rectifier diode. So for one current polarity will light the first LED, for the opposite the second LED, but in either way the reverse voltage across each LED is limited by a forward voltage by the other one safely way below the 5V, yet beside the two LED's and the single series resistor you need no other components at all.