I don't think it is technically practical, though I could be wrong. For an incandescent bulb, it would probably have to have two separate filaments and a switch. This might be doable, but it would expensive.

There are electric circuits used for controlling electric motor speeds that adjust to use only a portion of the 60 cycle wave but perhaps they are too expensive and bulky.

At least in the North American market, they do make dual filament bulbs and fixtures. The switch on the fixture selects which combination of filaments or off.

Anyhing else that would be included as part of an incandescent bulb would signficantly increase the price, and it would not be worth developing such a device with its days numbered. Developers could invent such a switch for electronig flourescent ballasts though, as that is the near future.

I sugget one invest in a lamp dimmer otherwise.

3-way light bulbs have been around for years.

This has nothing to do with the topic, but I really like those mini-fluorescents that have the ~6500k color temperature (blue cast). They make it very easy to concentrate.

Yes, three-way bulbs have been around for decades, but they require a special socket and switch. The poster was suggesting a bulb that would work in a standard socket.

BTW, turning a hot bulb with your fingers is a bit hazardous. That might be a liability issue.

I was just now thinking about how such a device could work and I came up with an idea. The contact in the center of the bulbs base could be used as a simple pressure switch. Normally, if you screw the light bulb in until in just makes contact, the power will flow through the contact, which has a resistor, and the light will shine with low wattage. If you screw the light down farther, it will press the contact down until it touches another contact behind it. this allows the current to by-pass the resistor and you get higher wattage. The problem with this design is that the resistor will get hot, which could damage the socket. Still, it might work okay if the power drop isn't very much, though that might defeat the whole purpose of the device.

Light bulb sockets are wattage rated for the most part. Ever see the little tag stuck to 'em that says somthing to the effect of "Do not use bulbs higher than 60 watts"? No? Probably got burned off by a higher than recommended wattage bulb.

While it's true that designing a multiple wattage bulb wouldn't be too difficult teaching people how to determine whether it's safe to use one in a particular application might be. BTW, I just tested a 3-way into a normal socket. It works on the low watt setting. The manufacturer seems to have prepared for the inevitable.