Connecting a MacBook Air with Thunderbolt 2 to a Monitor with HDMI and USB-C

Question

I have a 13-inch MacBook Air Early 2015, resolution 1440 × 900 with thunderbolt 2 and USB-A. I want to connect it to a bigger display. Right now I am considering to buy an LG 27UK850-W 4K 27 inch Monitor (resolution 3840x2160) which has HDMI, USB-C, DisplayPort and USB Downstream Port. Can I connect my MacBook and the monitor with the following connections:

1. MacBook Air -> Thunderbolt 2 Cable -> Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter -> LG 27UK850-W 4K Monitor

2. MacBook Air -> USB-A to HDMI adapter -> HDMI -> LG 27UK850-W 4K Monitor

Would there be any limitations with the display quality? Which one is the best way to connect the devices or do you have any other suggestions?

Answer 1

I wouldn't recommend any of those. Instead get an ordinary mini-DisplayPort to DisplayPort cable and connect the monitor with a plain cable instead of adapters.

The 2015 MacBook Air cannot be charged over the USB-C port in any case, so you cannot benefit from that feature of the monitor right now. However in the future you might have a newer computer, and then the USB-C port with Power Delivery might come in handy.

Answer 2

Whenever I post an answer regarding video, I usually corrected by some other user. Lets see how far I get this time.

everymac.com states the following for a MacBook Air "Core i5" 1.6 13" (Early 2015):

2nd Display
Support:	Dual/Mirroring*
Max. Resolution:	3840x2160 (4K)*
Details:	*Although Apple originally only reported that this model could support a single external display up to 2560x1600, third-parties discovered that it actually could support a 3840x2160 (4K) display, and Apple subsequently revised their official documentation to confirm this, as well.

Apples Technical Specifications states for MacBook Air (13-inch, Early 2015):

Graphics and Video Support

• Intel HD Graphics 6000

• Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on an external display, both at millions of colors.

• Thunderbolt digital video output

  ◦  Native Mini DisplayPort output
  ◦  DVI output using Mini DisplayPort to DVI Adapter (sold separately)
  ◦  VGA output using Mini DisplayPort to VGA Adapter (sold separately)
  ◦  Dual-link DVI output using Mini DisplayPort to Dual-Link DVI Adapter (sold separately)
  ◦  HDMI audio and video output using third-party Mini DisplayPort to HDMI Adapter (sold separately)

According to DisplayPort.org, "4K Ultra HD refers to 3840 x 2160 pixels".

I assume then you would probably what a mini DisplayPort to 4K HDMI adapter (or cable) and monitor with HDMI input and at least 4K resolution.

I believe the fact that the Mac's mini DisplayPort can also do Thunderbolt 2 is not really relevant in this case.

Answer 3

The LG 27UK850-W is not a Thunderbolt monitor. It expects a DisplayPort alt-mode signal from its USB-C port, so proposal #1 definitely won't work. While the Thunderbolt 2 port in the MacBook Air natively supports mini DP output, as soon as you connect it to Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter, the signal coming out of the other end is purely Thunderbolt.

With the second proposal, it will work but is not ideal. USB-A display adapters typically rely on a tech known as DisplayLink, which is what enables USB to output a video signal. Not all adapters support your monitor's native resolution and refresh rate, so if you were to go this route, best to carefully check the adapter's maximum supported display mode. Some adapters top out at 3840x2160 @ 30 Hz, which is fine for watching movies, but will feel noticeably laggy with basically any other task.

As @jksoegaard has said, getting a regular Mini DisplayPort to DisplayPort cable will be the best option, cost and image quality considered. Is there any particular reason why you are considering your proposed approaches?