Can you daisy chain this from the LG UltraFine 5K Display?
I already own this display (the LG UltraFine 4K) and I'm thinking of additionally purchasing the 5K display for use with my 2018 13" MacBook Pro with Touch Bar. Can the 4K display be connected to one of the output USB-C ports on the 5K display, thereby daisy-chaining it? I would prefer not to connect the two displays directly to my laptop, if possible.
- Asked by fn from San Francisco
LG UltraFine 4K Display
Product No Longer Available
1 Answer from the Community
The LG UltraFine 5K Display is a Thunderbolt 3 display which uses both DisplayPort connections of the computer's Thunderbolt controller. The Thunderbolt controller sends both DisplayPort signals to the Thunderbolt controller of the LG UltraFine 5K over the Thunderbolt cable. The Thunderbolt controller in the LG UltraFine 5K converts both Thunderbolt DisplayPort streams back into DisplayPort to be used by each half of the display (the left and right sides) to support 5K resolution.
That is also the reason why the LG 5K display does not have a second Thunderbolt 3 port - because it is required for one of the DisplayPort signals for one half of the display. The other DisplayPort signal comes out of a DisplayPort connection of the Thunderbolt controller of the display (think of a Thunderbolt 3 dock where you can connect one display to the second Thunderbolt 3 port of the dock, and another display to a DisplayPort output of the dock).
The Thunderbolt controller of the computer does not have a third DisplayPort connection, and since the LG 5K uses two DisplayPort connections (over Thunderbolt), an LG 4K display cannot be daisy chained to the LG 5K display.
Also, since a Thunderbolt controller only has two DisplayPort connections, if you connect a LG 5K to one side of the MacBook Pro, then a second display must be connected to the other side of the MacBook Pro (there's one Thunderbolt controller per side of the MacBook Pro). One 5K or two 4K per side of the MacBook Pro can be connected.
The USB-C ports of the LG UltraFine 5K only support USB. They do not support DisplayPort because there is no other DisplayPort signal on the Thunderbolt cable that can be used and the display has no other DisplayPort inputs.
It might be possible to use a USB to DisplayPort converter (research devices that use DisplayLink, find examples at the DisplayLink or plugable websites) but they don't perform like real displays and may have issues in macOS.
- Answered by Joseph V from Fort Langley