Question about connection protocol for USB-C monitors

[jent]

I recently bought a new monitor (an LG 27UK850-W 27" 4K UHD IPS Monitor) and one of the connection options is USB-C, which I'm using on my MacBook Pro.

In System Information.app, it describes the external monitor connection type as "Thunderbolt/DisplayPort," and I'm using the USB-C-to-USB-C cable that came with it. I'm just wondering what the actual protocol or connection type is since I know with USB-C there tends to be an overlap in many communication protocols using the same connector type. Just curious, so thanks for any information!

While I'm posting this, I'll also ask if it's normal for an external monitor to not have a brightness control setting within macOS. It doesn't seem to auto-dim like the built-in MacBook Pro display does, and the colors look all strange when enabling HDR, so I'm curious what's causing these apparent shortcomings.

 

[velocityg4]

The LG website says USB C and HDR Effect. So the connection is just USB not Thunderbolt. Nor does it support HDR. It just stimulates it. Probably through a menu setting.

Most monitors can not be controlled from OS. Any controls will be through the OSD (On Screen Display).

 

[joevt]

I recently bought a new monitor (an LG 27UK850-W 27" 4K UHD IPS Monitor) and one of the connection options is USB-C, which I'm using on my MacBook Pro.

In System Information.app, it describes the external monitor connection type as "Thunderbolt/DisplayPort," and I'm using the USB-C-to-USB-C cable that came with it. I'm just wondering what the actual protocol or connection type is since I know with USB-C there tends to be an overlap in many communication protocols using the same connector type. Just curious, so thanks for any information!

While I'm posting this, I'll also ask if it's normal for an external monitor to not have a brightness control setting within macOS. It doesn't seem to auto-dim like the built-in MacBook Pro display does, and the colors look all strange when enabling HDR, so I'm curious what's causing these apparent shortcomings.

It's not a Thunderbolt display so there's no Thunderbolt connection/signal.

The signals over the USB-C cable is called USB-C DisplayPort Alt Mode. The signals are DisplayPort for the display and USB for the USB features of the display.

For a 4K 60Hz display, the DisplayPort signal is probably four lanes (link width) of HBR2 (link rate). HBR2 only requires a DisplayPort 1.2 cable. This is confirmed by the manual.

The display supports HDR10, so the DisplayPort version is probably DisplayPort 1.4. The manual does not mention DisplayPort 1.4 though. There is an option to enable/disable DisplayPort 1.2 but the manual doesn't say if that switches the display to DisplayPort 1.1 or 1.4. I wonder if HDR works for both HDMI and USB-C/DisplayPort inputs?

For connection type and version, the output of the following command will have that info (for Intel Macs with modern Intel or AMD graphics). Try it for each input of the display, with and without DisplayPort 1.2 selected. Use a different filename for each:
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_a.txt 2>&1

With Four lanes of DisplayPort, the USB-C cable can only support USB 2.0. The product page says the downstream USB ports support USB 3.0, but maybe that's only available when using one of the other connectors (HDMI or DisplayPort) for the video signal (because USB 3.x uses two of the super speed lanes used by DisplayPort). That conclusion is not explicitly stated by the manual - it says that USB 3.0 is enabled when the USB-C port of the display is connector to a USB-A port. My conclusion would be correct only if USB 3.0 is automatically enabled when the display input is set to the HDMI or DisplayPort port even if the USB-C port of the display is connected to a USB-C port.

The LG website says USB C and HDR Effect. So the connection is just USB not Thunderbolt. Nor does it support HDR. It just stimulates it. Probably through a menu setting.

I think "HDR Effect" is only for content that is not HDR. See the manual, page 22. Otherwise, the display is supposed to support real HDR.

 

[jent]

Thank you both for the replies! I don't plan on using the USB ports on the monitor but I was just curious about the connection type since my vague understanding is that USB-C is a connector but is a shape that is used by other communication protocols, so I was wondering what the actual display connection is between the monitor and the computer.