old house, porch light has no ground

I bought a porch light and would like to install it myself. My house is old though, probably 50+ years? In any case, I removed the old porch light and there are only two wires coming out of it, a black and white one. I'm not an eletrician so I am clueless about wiring. I was just going to follow the instructions that came with the lamp I bought. Anyway, there are also black and white wires on the lamp in addition to a green wire, which is the ground. The instructions call for the lamp to be mounted to a "plate" and the plate is to be mounted to the electrical box where the old lamp was mounted to. The green ground wire is to be connected to a "grounding screw" that the mounting plate is on. Based on this, am I grounding the lamp or what? Because the ground wire is connecting to the plate and the plate is connecting to the box, and the box, well, who knows what's going on with the box? In any case, I don't understand the difference between grounded or ungrounded, can someone please explain it to me in layman's terms?

The second thing is, I noticed that in hardware stores, they sell these "3 prong" adapters for older homes with two prong outlets. Basically, its a 3 prong plug that plugs into the 2 prong outlet you currently have. There is a little metal loop that you screw to the screw between the two oulets on your outlet plate (the same screw that holds the outlet plate to the wall. If you're house is not grounded, what is the purpose of this 'adapter'? and how is screwing the little metal loop on the adapter to the wall plate doing any good?

Ok, final thing, in the even the house is not grounded, and you use a heavy duty surge protector/power strip (they are three pronged, but lets assume you plug it in using the above mentioned "adapter"), how does the fact that your house is not grounded affect the power strip/surge protector? How will it affect your equipment that is plugged into the power strip?

Thanks everyone for your time!

 

You may or may not be grounding the lamp. But connect the green wire anyway. It can't do any harm and it might do some good. Grounded is safer than ungrounded, but you have to live with what you've got. A 50 year old house is missing many modern safety features, just as a 50 year old car doesn't have seat belts, antilock brakes, or airbags.

The screw on a receptacle cover may be grounded. When you buy the adaptor, also buy a $7 outlet tester. Plug in the adaptor and attach the screw. Then use the outlet tester on the adaptor. If the outlet tester shows "open ground" then I would not use the adaptor. There are alternatives -- come back and ask if you get to this point.

A surge protector may be worthless without a ground, or it may simply be less effective. Some of the most important features of a surge protector require a ground. This is why people in older homes often have an electrician install a new grounded circuit for their computer or expensive electronic equipment.