Turning out the lights seems pretty easy to me but maybe it's because my parents constantly told me to do it when I was young. I know I feel like I tell my kids A LOT. I’ve found it does become a habit if done over and over enough times. It's also a quickly forgotten habit- thus the nagging of the children. But it does save energy so it's worth the nagging in my opinion. I’ve read that lighting can count for anywhere between 20-50% of home and/or office energy consumption. I think this number might be a little off with more energy effiecient options available nowadays.

Both incandescent and fluorescent light bulbs lose some of their lifespan when being turned on and off. But the rule in our house is turn out the light when you leave a room. I don't like the idea of wasting energy and a little lifespan on a bulb that uses more energy anyway isn't worth it. (LEDs aren't effected by the on/off switching)

The below chart is a financial reason to upgrade light bulbs when one burns out. I found the data on the Lowes website and my energy bill. I rounded my KWh per hour price slightly up from my bill.

lightbulb facts

Initially, I was replacing our incandescents with fluorescents. We have no incandescents left in our house and the Lowes site says they are being phased out there too. Now I’m replacing fluorescents with LEDs. I like that LEDs are not fragile, and even if one did break, I wouldn't have to clear the room and open the windows to clean it up (not cool, fluorescents!). LEDS last a long time too; my daughter got a starry LED nightlight about 6-8  years ago. The stars permanantly enclose the LEDs. At the time I thought the light was nice but when the bulbs burn out, the nightlight is trash. It's still working along with the rest of the LEDs we've bought in the past 4 or so years.
Even just 4 years ago, LEDs were huge investment. They still aren't cheap but I feel like they are much more affordable now, especially knowing first hand about the longevity and energy savings. Fortunately, there is also more variety now. They are not blindingly bright anymore. All of this change toward less energy use and better product in mainstream America gives me hope. And I'm not just seeing it in lightbulbs. I like to think a lightbulb is going on in the earth-mindset.