Material:

Copper tape
To-go coffee up
Coffee cup holder
3 leds
wires
2 button batteries
battery holder
regular tape
double tape
soldering iron
soldering machine

Procedure:
First I pick 3 leds and the colorful wire out, I soldered 3 led’s long legs to the on side of the colorful wire. Then I cut another half of the colorful wire to solder them with the leds. After that, since one side of those three color wires are conected, I solder them to one of the button holders’ wire. Then, I used the copper tape to wrap the coffee cup, and also use the blue regular tape to tape all the wires on the coffee cup holder and leave one of the button battery’s wire and one side of the colorful wire untaped. Later on, I used the double tape to tape the coffee cup holder, and put it on the coffee cup.

Since the copper tape is conductive, thus when two wires that untaped touched the copper tape, leds will light up.  As a result, when I hold the coffee cup, the leds will light up, and if I leave the coffee up on table, it is not gonna be light up.