There is a HUGE variety of sockets, including Mogul (commercial outdoor lighting) Medium base (Edison) socket, mini-candelabra (Night Lights and chandeliers, etc.), Bayonet (some microwave oven lights) and bi-pin bases in several sizes (Halogen undercounter) and so on...

Manufacturers who want to sell CFLs and LEDs must pick a lamp and base format to start with. Since the Medium Base Edison socket has been the common accepted base, and is the most prevalent, that is where the chose to enter the market.

If you want to sell something new, perhaps the best strategy is to make it look like the thing that you are trying to replace?

I have switched over almost entirely to LED, and I sure as heck didn't want to replace every fixture in my house to do it.

Whats wrong with the fixtures? A lot of things in a home are of old designs.

It wasn't a very good design to begin with -- if the lamp isn't polarized and it's plugged in with hot connected to the socket shell, you can get a tickle when removing a bulb. There's also normally a thin cylinder of cardboard separating the socket shell from the (metal) outside of the socket.

Interestingly, I lived in a house that had a few of the Edison sockets in the baseboard with two-pin outlet adapters screwed into them. Before the US standardized on an outlet design, bulb sockets were used as outlets as well!

I wish I understood why that happens. I don't have a good handle on electricity.

120V A.C. power as provided in the US has a hot and neutral lead. The hot lead alternates between about +170V and -170V(*) 60x per second with respect to the neutral lead.

The neutral lead is tied to ground in the fuse box. Therefore, since it's forced to have the same potential as the world around it, coming in contact with it is (generally) harmless.

The neutral lead should (obviously) be connected to the shell of the lamp socket, not the tit. However, if a lamp can be plugged in either way (pins the same size), you can end up with the tit connected to neutral and the shell connected to hot. The switch generally only switches the tit, so switching off the switch will still keep the shell hot. Touching the hot line can be painful.

(*) - yep, 170V. 120V is the average voltage provided.

LED bulbs won't work if they're connected to a battery with the leads reversed. Is that true in household bulb sockets also? Are household LED's 120v or 12v with a transformer in the bulb?

Not true, since A.C. switches between plus and minus. Reversing hot and neutral is more a safety issue than a functional one.

I don't think that LEDs contain a transformer -- probably a switching power supply to step the voltage down to something usable by the LED cluster.

Most "replacement" style LED bulbs contain a built in transformer (driver) and also the circuits for dimming. The transformers generate heat and require sinks and ventilation.

Often no transformer, just a switching power supply that uses transistors to switch 120V into a capacitor quickly, keeping it charged to the correct DC voltage to run the LEDs. Isolation isn't needed since the unit is insulated on the outside.

I have seen the switching power supplies in applications like under cabinet puck lights and tape lights, but not in direct replacement bulbs.

Simply put. The neutral hooked to the shell of the socket means as you unscrew the lightbulb the centre contact of the bulb breaks connection. So even if the glass portion is moist or has some conductivity for some reason. The bulb is disconnected and the shells only reference is to the neutral or ground portion of the socket that is still hooked up

. Reverse the power connections and there is a possibility of a tingle as the shell of the socket remains connected to the bulb. Actually the Edison socket type e26 in north America? This was a good design and perhaps hard to really improve on.

What about a simple bi-pin plug with a locking tab?

You have any recommendations for brand? I was looking at replacing 5-6 of our BR40 size bulbs (I think thats what they are)...they go in our kitchen can lights. I was hoping to keep costs down, maybe $7-10 per bulb.

Interesting. When you get nomed an Academy Award for Cinematography let me know. Until then I will stick with my guy who, while he has yet to win, at least has picked up a nom.

Well, that may be too harsh. In our business the picture exists in the mind of the Director before it exist on a recorded medium. Recording the image is more of a technical skill.

And getting an image in lower light means one less lighting set-up. It is all too technical for me which is why I let them do it.