An electronics proffesional has told me that i can get a couple of volts with that stuff.
Are you shure it cant power a LED?
Yes, you can! I am a proof! Here's my full story about it-
My house has a metal as a roof and it's almost 12x12 meters wide. All pieces of metals (roofs) are connected electrically. So I got 12x12 wide 'antenna' for radio waves. The roof is not grounded because my house has been made by wood (not by cement and rods).
First I made a simple crystal radio- A coil, germanium diode and a earpiece, I could hear pretty audiable voices of stations of my own country Nepal; also received from China, India etc during night. Later I had to add 1nF cap across coil to eliminate stations overload.
(I earthed one meter aluminium plate for earth connection a poured water there for wet/nice earthen).
Once, my body was earthed, and I touched to roof by tongue tip (I do not remember why I did so), and found that the metal was little sour everywhere in taste!
Then I found that it's a radio shock, wow! Then I connected a high bright red LED, scrapped from an optical mouse then got a dim light. It was very interesting! Also connected a white medium power LED (1/2 watt maybe), also got very dim light! I measured AC volts from roof to earth and got 11V AC during open circuit, on my poor DMM.
It would be totally free (no bill for electricity) 'indicator' of RF existance on roof! I could connect a LED permanently there, but afraid to killing 'lightning' around summer.