How to manually turn on/off display screen?

Hi, I'm using a Inspiron 15 7000 Series 7559. I would like to turn on/off my display screen while still running my programs in the background. I would like the option to do this when I'm listening to audio books on YouTube or when I have my laptop connected to my TV. Its really annoying having the screen running even at its dimmest when it doesn't need to be on, so is there anyway to black out the screen then turn it back on when needed while still keeping YouTube, ect. running?

I did do some research online and found some sites where I could download programs to turn off the LDC display, but they seem sketchy at best and since this is a basic feature I thought maybe dell has it tucked away somewhere.   

Anyway any help would be greatly appreciated and thanks for you time.