There was initial discussion between dave harper and woofer that eco and normal modes enabled some sort of dimming but in looking at the manual it appears this is not the case. The dynamic power mode is only if you're using custom and adjust it manually. And you only get the full black if you hit hide on the remote.
Video: JVC RS4500 135" screen in pure black room no light, htpc nvidia 1080ti.
Audio: Anthem mrx720 running 7.1.4, McIntosh MC-303, MC-152, B&W 802d3 LR, B&W HTM1D3 center, B&W 805d3 surround, B&W 702S2 rear, B&W 706s2 x 4 shelf mounted for atmos, 2 sub arrays both infinite baffle: 4x15 fi audio running on behringer ep4000 + 4x12 fi audio running on 2nd ep4000.