Safe to close macbook pro lid while using a second monitor?

[Bathplug]

Is it safe to close the lid while using a second monitor as the default one with a keyboard and mouse? I don't think the mac gets any hotter and when the lid is closed. The screen and the apple light turn off so I think its off and not dimmed but if I lift the lid up slightly and feel the mac screen its warm from resting over the macbook pros keyboard area. Will this damage the screen from the heat? or is there a way to leave the lid open but keep the mac screen turned off?

Thanks

 

[aeboi]

Yes it's completely safe to use it in clamshell mode.