Is there a way to turn off all  lights in Poser 11?

Delete them all - there's a script - or simply switch their values to zero.

Or on the properties tab, uncheck the on switch.

People, read the question!  The OP wants to turn off ALL lights in the scene at once.  Follow the Path in the screencap below:

Once the XLC Panel opens, right-click Light on the banner (highlighted) which will open the Parameters window, and there you will find the context field for turning on/off lights (highlighted).

This is how it's done in P11.

I did read the question.  Can't see where it says "at once", though.  Either way I suggested - and the others - work.

It's a matter of implication but you are right, the OP was not explicitly clear about how to turn off the lights.  All should be good now; all the bases have been covered.

Thank you. My apologies for not being clearer. :)

That's a useful trick, especially when you're trying to set a scene with 'luminous' stuff, as super-ambient and/or Cycles' emission.

One other way :D

https://sharecg.com/v/57963/gallery/8/Script/Light-Toggle

Designed so you could set up working lights, toggle them off and set up the render lights, and then toggle back and forth as needed

Bill

Thanks willyb! That's precisely what I needed.

my free light set here at Renderosity includes a preset that deletes all lights and one that loads three global lights that do not illuminate when rendered for those times you are using an HDRI or glowing objects.

https://www.renderosity.com/freestuff/items/86815/studio-lights-for-poser-12-and-poser-11