I heard that you use power strips for decorative lighting to eliminate wasted energy, but you might overload the circuits so it’s dangerous.
The 電 is what powers electric things. Many times, these electric things light up (especially back in the day, when electricity did this a lot more than other things). So, you have "lighting." Then, you have decorate. So, if you decorate with lighting, you have decorative lighting.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.