Cavemen were mostly in the dark I believe. Fire was a big help. Every now and then the fire would go out and that was their power outage time.
I had a recent power outage. All the power in my neighborhood was out for over 12 hours. I could not understand why it was so dark. Then I realized that at night even though the lights are off. All the LED lights on my clock, phone, TV, VCR and various other electronics did light up my darkened house a bit. I was surprised at how many of these little red lights I had. When they went out, during the power loss, it really made a difference. Sometime it amazes me what I learn just sitting in the dark.