Same problem here but I'm using LightDM. Everything works when I'm using Intel driver. When I'm switch to NVidia via nvidia-settings or prime-select then restart LightDM, LCD in my laptop is turning off.
Here is syslog messages:
Apr  1 07:24:55 drag0n kernel: [  350.538587] bbswitch: enabling discrete graphics
Apr  1 07:24:55 drag0n kernel: [  350.884185] [drm] Initialized nvidia-drm 0.0.0 20150116 for 0000:01:00.0 on minor 1
Apr  1 07:24:55 drag0n kernel: [  350.884189] NVRM: loading NVIDIA UNIX x86_64 Kernel Module  346.47  Thu Feb 19 18:56:03 PST 2015
Apr  1 07:24:56 drag0n kernel: [  351.643158] vgaarb: this pci device is not a vga device
Apr  1 07:24:56 drag0n kernel: [  351.643440] nvidia 0000:01:00.0: irq 56 for MSI/MSI-X
Apr  1 07:24:56 drag0n kernel: [  351.645534] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  351.645578] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  351.645600] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  351.645621] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  351.645640] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  351.645659] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  351.645691] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  351.645712] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:56 drag0n kernel: [  352.248312] ACPI Error: Field [TMPB] at 290816 exceeds Buffer [ROM1] size 262144 (bits) (20140424/dsopcode-236)
Apr  1 07:24:56 drag0n kernel: [  352.248317] ACPI Error: Method parse/execution failed [\_SB_.PCI0.PEG0.PEGP._ROM] (Node ffff880227076190), AE_AML_BUFFER_LIMIT (20140424/psparse-536)
Apr  1 07:24:56 drag0n kernel: [  352.258318] ACPI Warning: \_SB_.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
Apr  1 07:24:57 drag0n kernel: [  352.370932] vgaarb: this pci device is not a vga device
Apr  1 07:24:57 drag0n acpid: client connected from 5558[0:999]
Apr  1 07:24:57 drag0n acpid: 1 client rule loaded
Apr  1 07:24:57 drag0n bumblebeed[2991]: [XORG] (WW) "glamoregl" will not be loaded unless you've specified it to be loaded elsewhere.
Apr  1 07:24:57 drag0n bumblebeed[2991]: [XORG] (WW) "xmir" is not to be loaded by default. Skipping.
Apr  1 07:24:57 drag0n bumblebeed[2991]: [XORG] (WW) NVIDIA(0): Unable to get display device for DPI computation.