LG UltraFine 5K - Owners Thread

[sadandsalty]

Hey everyone, first time posting here. A little about my situation:
- 2 LG Ultrafine 5k monitors
- Work computer: 2019 16" Macbook Pro with Intel 5500M 4GB video card
- New personal computer: 16" M1 Max
- Razer Thunderbolt 4 dock and Caldigit Element Hub

I have my two Ultrafines connected to the downstream ports of the Razer dock, which is in turn connected to my work computer (2019 16") via a single TB4 cord. I'm getting a 5k resolution on both monitors.

Just got the M1 Max a couple days ago, and when plugging into the Razer dock, my monitors are outputting a max of 4k. I've attempted using TB4 cables for the downstream ports as well as trying out the Element hub. No dice. I am getting 5k to both monitors when directly connecting the monitors to the M1's ports.

I saw in this post by @joevt that:

An LG UltraFine 5K requires two DisplayPort 1.2 connections over Thunderbolt (two tiles of 2560x2880 at 483.37MHz). Each connection is 14.5 Gbps. There's no way you could connect two of them to a single Thunderbolt port - that would require 58 Gbps but Thunderbolt can only do 40 Gbps.

Which makes sense to me, but doesn't explain why the 2019 16" is outputting 5k through both the Razer and Element docks. I'm a layman here, but does it have anything to do with the 5500M supporting DSC?

 

[joevt]

Which makes sense to me, but doesn't explain why the 2019 16" is outputting 5k through both the Razer and Element docks. I'm a layman here, but does it have anything to do with the 5500M supporting DSC?

The LG UltraFine 5K displays do not support DisplayPort 1.4, HBR3, or DSC.

I suppose it would be possible to create a magical HBR3 + DSC to dual HBR2 adapter (not an MST Hub - more like a video wall processor) and connect the output of that to the DisplayPort inputs of a Thunderbolt controller to be transmitted to the LG UltraFine 5K but it's unlikely.

No, what's happening is that you are probably only getting 4K to the displays. That is strange because if you connect one display then the second should remain blank. Maybe you had the displays connected at startup and the Thunderbolt controllers/drivers decided to give one DisplayPort connection to one display and the other DisplayPort connection to the other display. If you connect the displays after startup one at a time, then you should see the expected behaviour where the first display works at 5K and the second is blank. Or maybe you are connecting the displays with a USB-C (non Thunderbolt) cable - that would force each display to only have one DisplayPort connection and limit them to 4K60 (or maybe 5K39 if you want to experiment).

Check the Thunderbolt tab in System Information.app. Check that each display is connected with 40 Gbps x1 link rate and x2 link width. If you used a USB-C cable, then the link rate would be 20 Gbps x1.

Use SwitchResX to verify the output timing. In the Current Resolutions tab for the display, double click the currently selected resolution. It will show the output active pixels (I expect 3840x2160@60Hz with 522.61MHz pixel clock) and the scaled resolution (5120x2880). The LG UltraFine 5K normally uses two 483.37MHz pixel clock connections which macOS fakes as 938.25MHz (SwitchResX will report the fake only if it's actually outputting 5K).

Use the AGDCDiagnose command to see if DSC is enabled for the displays (it will not be). It should also show output resolution, output timing, and output pixel format (probably 10bpc RGB). It will also show the DisplayPort connections that are being used, their link rate and link width (number of lanes).

If the displays are running at 4K, you could try using SwitchResX to create 5K timings between 30 and 40Hz (one person has reported trying this and got up to 600 MHz pixel clock which is like 39 Hz). But you'll probably just move one of the displays to a different Thunderbolt port and we won't get confirmation that a lower refresh rate like 39Hz will work.

 

[sadandsalty]

Use SwitchResX to verify the output timing. In the Current Resolutions tab for the display, double click the currently selected resolution. It will show the output active pixels (I expect 3840x2160@60Hz with 522.61MHz pixel clock) and the scaled resolution (5120x2880). The LG UltraFine 5K normally uses two 483.37MHz pixel clock connections which macOS fakes as 938.25MHz (SwitchResX will report the fake only if it's actually outputting 5K).

Wow, you're absolutely right. After checking SwitchResX, I confirmed that both computers are scaling to 5K. Even though the 2019 Intel's Display tab is showing a max res of 5120x2880 for both screens and the M1 Max is showing 3840x2160, SwitchResX indeed shows the settings you described.

I guess I'm the joke here with thinking I had 5K the whole time! Thanks for your help, I'm going to play around with a lower refresh rate.

 

[Amethyst1]

I'm going to play around with a lower refresh rate.

Do you have the older (27MD5KA) or the newer (27MD5KL) UltraFine 5K?

I guess I'm the joke here with thinking I had 5K the whole time!

Don’t think too much about it The problem is macOS isn’t showing the actual resolution the screen is running at anywhere in the GUI — even System Information.app shows framebuffer size instead.

 

[sadandsalty]

Do you have the older (27MD5KA) or the newer (27MD5KL) UltraFine 5K?

I have both, the 27MD5KL is my primary in landscape and the 27MD5KA is my secondary in portrait.

Don’t think too much about it The problem is macOS isn’t showing the actual resolution the screen is running at anywhere in the GUI — even System Information.app shows framebuffer size instead.

Thanks, I'm really thankful for SwitchResX showing exactly what's going on!

 

[Amethyst1]

I have both, the 27MD5KL is my primary in landscape and the 27MD5KA is my secondary in portrait.

Cool setup. I’m asking because 5K at lower refresh rates using a single DisplayPort stream has only been confirmed to work on the —KL so far. But that should not deter you from trying it on the —KA!

 

[petterihiisila]

I'm planning on demoting Ultrafine 5k into a secondary monitor, as I might get an M1 Max later this year. The primary could be bigger, I'm eyeing at LG 32UN880-B. It's a USB-C 4k monitor.

Is anyone daisy chaining a 4k USB-C monitor behind a TB3 5k? Would it work as usual? I'm mostly worried about is bandwidth: the LG 5k USB-C downstream ports are limited to 5 Gbit/s. If 4k/60 Hz is not to be expected from that port downstream, then it's not such a good idea.

Another candidate for a bigger primary display would be a TB3 monitor: 32UL950-W. It has a downstream TB3 port, but again I wonder if that port could be used to daisy chain an LG 5k.

So, the two variations are:

TB3 --> Ultrafine 5k --> USB-C 5 Gbps --> LG 32UN880-B

and

TB3 --> 32UL950-W --> TB3 --> Ultrafine 5k

Thoughts on that?

 

[Amethyst1]

Is anyone daisy chaining a 4k USB-C monitor behind a TB3 5k? Would it work as usual?

The two DisplayPort streams that are carried over a TB3 cable are both used by the UltraFine 5K, each driving one half of the display at 2560×2880. There's no stream left for daisy-chaining another DisplayPort/TB/USB-C display behind it.

Another candidate for a bigger primary display would be a TB3 monitor: 32UL950-W. It has a downstream TB3 port, but again I wonder if that port could be used to daisy chain an LG 5k.

Since one of TB3's two DisplayPort streams is used by the 4K monitor in this case, the UltraFine 5K will only run at 4K. It needs two streams for 5K.

 

[joevt]

The two DisplayPort streams that are carried over a TB3 cable are both used by the UltraFine 5K, each driving one half of the display at 2560×2880. There's no stream left for daisy-chaining another DisplayPort/TB/USB-C display behind it.

Don't forget that the USB-C ports of the LG UltraFine 5K are only USB - they are not Thunderbolt and they don't support USB-C DisplayPort Alt Mode so they couldn't be used to connect a display even if there was a third DisplayPort signal on the Thunderbolt cable.

As an aside, it might be possible to put more than two DisplayPort signals (ignoring DisplayPort MST since macOS doesn't support it) on a Thunderbolt cable using an eGPU like the Sonnet eGPU Breakaway Puck RX 5500 XT/5700 or BlackMagic eGPU since their GPUs are connected to the DisplayPort inputs of their Thunderbolt controllers - that way two DisplayPort connections could come from the Mac and two could come from the eGPU. With 2 HBR2 signals for the LG UltraFine 5K, there would only be bandwidth remaining for an RBR display (1080p). Actually, the LG UltraFine 5K doesn't require all the bandwidth of HBR2 so it could be possible to connect a HBR display but then you would need some special software to make the connection (like how Apple forces 2 HBR3 signals to the Apple Pro Display XDR when DSC is not supported).

 

[petterihiisila]

The two DisplayPort streams that are carried over a TB3 cable are both used by the UltraFine 5K, each driving one half of the display at 2560×2880. There's no stream left for daisy-chaining another DisplayPort/TB/USB-C display behind it.

Since one of TB3's two DisplayPort streams is used by the 4K monitor in this case, the UltraFine 5K will only run at 4K. It needs two streams for 5K.

Thank you @joevt. Concise and informative as usual. I can derive the rest of the plan from here. ?

Luckily the M1 Max has some ports to spend.

 

[joevt]

Wow, you're absolutely right. After checking SwitchResX, I confirmed that both computers are scaling to 5K. Even though the 2019 Intel's Display tab is showing a max res of 5120x2880 for both screens and the M1 Max is showing 3840x2160, SwitchResX indeed shows the settings you described.

Do you notice an improvement after switching to 5K from 4K? I suppose it must be a subtle change if you didn't realize it wasn't working at 5K previously. Or more likely, you didn't have much 5K experience before this so you didn't know that 5K could look better than what you were seeing.

You haven't said how you get them both to work at 4K.

1) Normally, only one should work if you connect one first and then the second after that.
2) Are they connected with Thunderbolt 20 Gbps or USB-C (instead of Thunderbolt 40 Gbps)?
3) Are they connected before boot?
4) Do you connect them at the same time by connecting them to the Razor dock first and then connecting the razor to the Mac after that?

Is statement #1 false and connecting the second makes the first switch to 4K so the second can work? Or are you using #2, #3, #4 or some other method to get them both working?

I guess I'm the joke here with thinking I had 5K the whole time! Thanks for your help, I'm going to play around with a lower refresh rate.

Let us know if you are successful or not with the lower refresh rates.

 

[-Ryan-]

What is the best way to have dual sound output between iMac and Ultrafine? I have been using the Audio Midi Setup app as suggested by Apple since I got the monitor, but it's a bit of a workaround and it occurred to me maybe there is an app that is more user friendly.

 

[1369281]

What is the best way to have dual sound output between iMac and Ultrafine? I have been using the Audio Midi Setup app as suggested by Apple since I got the monitor, but it's a bit of a workaround and it occurred to me maybe there is an app that is more user friendly.

I use and recommend Klipsch ProMedia 2.1 speakers/sub instead. They are about $119 online and they will blow you away.

 

[Tsurara]

Is there any word on an update for the LG Software OSX Monterey? I have 2x displays connected via USB C to an M1 Max MacBook and I am getting some oddities like screen brightness inconsistencies which didn't exist with my Intel Mac. I believe the software support may solve this. Anyone heard anything?

 

[Grolubao]

Is there any word on an update for the LG Software OSX Monterey? I have 2x displays connected via USB C to an M1 Max MacBook and I am getting some oddities like screen brightness inconsistencies which didn't exist with my Intel Mac. I believe the software support may solve this. Anyone heard anything?

I mean it's discontinued, I don't expect any update

 

[saulinpa]

I mean it's discontinued, I don't expect any update

Not showing as discontinued in the US. Even when it is Apple sometimes sends out updates for older products.

 

[scott_donald]

Is there any word on an update for the LG Software OSX Monterey? I have 2x displays connected via USB C to an M1 Max MacBook and I am getting some oddities like screen brightness inconsistencies which didn't exist with my Intel Mac. I believe the software support may solve this. Anyone heard anything?

I get the brightness bug too on a Max with 2 x5k.

Hopefully apple fix it, got used to using the menu bar to fix. It doesn't happen every time.

 

[ataq]

I maybe get a great offer for a „perfect condition“ lg 5k from craiglist. I‘ve read about bugs and issues like ghosting etc… So what do I have to watch out for? Special model number or tests?
I will have the chance to testdrive the monitor with my macbook before purchase.
Thanks

 

[saulinpa]

I maybe get a great offer for a „perfect condition“ lg 5k from craiglist. I‘ve read about bugs and issues like ghosting etc… So what do I have to watch out for? Special model number or tests?
I will have the chance to testdrive the monitor with my macbook before purchase.
Thanks

Verify you get 5k when connected with a good TB3 cable. Spend some time with https://www.eizo.be/monitor-test/ to verify no stuck pixels or other video problems. 27MD5KL is new version 27MD5KA is old version. New version can connect at 4K to DP over USB-C and can do 94 watts of power for your MacBook. Check speakers, camera, and USB ports. Stand should raise, lower, and tilt but will be a bit shaky.

 

[Chris60549]

I maybe get a great offer for a „perfect condition“ lg 5k from craiglist. I‘ve read about bugs and issues like ghosting etc… So what do I have to watch out for? Special model number or tests?

Most important to check for image retention IMHO.

LCD Image Retention Test

Older model would be OK for me, I see no material advantage of the new version. Connecting an iPad at 4K to the new version destroys the point of buying a 5K display in the first place but YMMV.

 

[ataq]

Verify you get 5k when connected with a good TB3 cable. Spend some time with https://www.eizo.be/monitor-test/ to verify no stuck pixels or other video problems. 27MD5KL is new version 27MD5KA is old version. New version can connect at 4K to DP over USB-C and can do 94 watts of power for your MacBook. Check speakers, camera, and USB ports. Stand should raise, lower, and tilt but will be a bit shaky.

Most important to check for image retention IMHO.

LCD Image Retention Test

Older model would be OK for me, I see no material advantage of the new version. Connecting an iPad at 4K to the new version destroys the point of buying a 5K display in the first place but YMMV.

Very good tips, thank you both.
Is there a thunderbolt cable normally part of the package?

 

[-Ryan-]

Very good tips, thank you both.
Is there a thunderbolt cable normally part of the package?

Yes it should come with a TB3 cable and if you get the newer model it will also come with a USB-C cable.

 

[joevt]

anthony13 asked why Apple stopped support Target Display Mode. I speculated that Apple didn't have to stop supporting it - they just have to update the code to support the tiled displays.

I've done some testing of Thunderbolt Target Display Mode since I made this statement https://forums.macrumors.com/threads/displaylink-luna-display-2011-imac.2294250/post-30474454 . It appears that Thunderbolt Target Display Mode is more like DisplayPort Target Display Mode than I originally thought. It's not just software.

Back in the Thunderbolt 1 days, the 27 inch iMac had a Thunderbolt 1 controller with 2 DisplayPort inputs (for output to the Thunderbolt ports) and 1 DisplayPort output. The DisplayPort output is used to drive the internal display after a DisplayPort mux switches the input of the internal display from the GPU to the Thunderbolt controller's DisplayPort output (when the user types Command-F2 to initiate Target Display Mode). Thunderbolt Target Display Mode sends a signal to the source Mac to tunnel DisplayPort over Thunderbolt to the DisplayPort output of the target iMac (this is an interesting trick since the tunnelling is cross-domain).

For Thunderbolt Target Display Mode to work with tiled displays (iMacs with 5K displays), the iMac would need a Thunderbolt 3 controller with two DisplayPort outputs to get 5K. I don't think any Thunderbolt controllers have two DisplayPort inputs and two DisplayPort outputs so getting this to work would require some extra circuitry. One method would require disabling one of the Thunderbolt ports of the iMac. A better method would require adding another internal Thunderbolt controller.

It seems to me that the trick that allows a Mac to output to an iMac's internal display via Thunderbolt should work with any Mac with a Thunderbolt connected display as long as a path can be setup between the Thunderbolt DisplayPort input of the source Mac and the Thunderbolt DisplayPort output of the destination Mac. This should work with multiple displays as long as there's enough bandwidth. That means it should work with tiled displays like the LG UltraFine 5K (the DisplayPort outputs belong to the Thunderbolt controller of the LG UltraFine 5K display)... Of course this won't help with an iMac's display if that display cannot be connected to Thunderbolt (no mux switch to Thunderbolt DisplayPort output).

 

[ralphthemagi]

So the M1 Max can run two LG 5k Ultrafine Displays at full 5k without issue? I had just assumed that it would be able to, but now I’m seeing some conflicting information about whether this is truly supported. I use this setup in two different locations. This seems to be the only thread I can find with people who actually have this hardware and setup.

I see some people saying they don’t run at full 5k. Sometimes when I connect my current MBP (2016) to the displays one only connects at 4k and upscale to 5k and I hate it (but it’s a simple fix—just disconnect and reconnect), so if the new MBP (2021/M1 Max) can’t do native dual 5k with the 5k LG Ultrafine I will need to cancel my order.

 

[jterp7]

Anyone else have problems with hard drives not remounting after wake up from sleep (hub connected to ultrafine usb c port)