The short explanation
Two related settings. Backlight control says whether the display modulates its backlight in response to content. Backlight minimum luminance says how dark it can get — typically 25, 50, 75 or 100 nits.
Where you run into it
Both feed the tone-mapping decision. A source that believes the display can drop to 25 nits treats dark scenes differently from one that assumes a 100 nit floor. Get it wrong and shadows either crush or look milky.
On projectors this is often the difference between a picture that looks flat and one that looks right, because a default data block built around a television's assumptions rarely fits a projector.
How the DR HDMI 8K handles it
Backlight control and backlight minimum luminance are both settings in the DR HDMI 8K's Dolby Vision data block builder. Set them, click Create IF and Send DV, and the constructed block is stored in the unit and used whenever the DV flag is set to CUSTOM.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.