JamieIf you want to use your iMac as a monitor for your Mac or PC, this guide provides a detailed, step-by-step process for utilizing your stunning 5K iMac display.
There are various methods to set up your iMac as a monitor, but here, I’ll outline my preferred option: Luna Display.
This is the setup I rely on daily with my 2015 iMac and M1 MacBook Pro. Let’s begin!
The Advantages of Luna Display
While several alternatives exist for connecting your iMac as a display, they come with certain drawbacks:
- Target Display Mode: This only works on iMacs from before mid-2014, so your iMac probably won’t work. It also uses an old Thunderbolt connector that newer Macs don’t have.
- AirPlay to Mac: Since the release of macOS Monterey, you can use AirPlay on Macs. This feature allows you to use another Mac as a screen. However, it is limited to 4K resolution and is not compatible with PCs.
- Duet Display: You can use your iMac as a screen for Mac or PC with Duet Display. But it doesn’t work with 5K resolution or USB.
In contrast, Luna Display accommodates the full 5K resolution of your iMac, is compatible with both Mac and PC, and offers connectivity through USB, Wi-Fi, Ethernet, or Thunderbolt.
We made Luna Display so you could use your iMac’s full 5K resolution. We work on fixing problems we see, and Luna Display is a good example of this.
Why Is Target Display Mode No Longer Viable?
As previously mentioned, many guides still suggest using Target Display Mode for turning your iMac into a monitor.
However, this advice is outdated as of 2024. Target Display Mode was available on earlier iMacs from around 2010 and could be activated through the keyboard when connected via Thunderbolt cables.
This option is no longer practical for several reasons:
- Limited Compatibility: Target Display Mode is only functional on iMacs from mid-2014 or earlier, which most users do not possess.
- Outdated Technology: It relies on an older version of Thunderbolt that does not work with contemporary Macs.
- Resolution Restrictions: Even if you manage to set it up, Target Display Mode caps at a maximum resolution of 2560×1440.
Due to these factors, Target Display Mode is not a feasible option. Instead, consider using Luna Display to connect your iMac to your Mac or PC for full 5K resolution.
Below are the essential items you’ll need to get started.
Required Equipment For Setup
1. A primary Mac or Windows PC to link to the iMac.
2. An iMac running macOS 10.15 or later for the USB connection mentioned in this guide (10.13 if you prefer to connect via Ethernet or Thunderbolt).
3. Luna Display USB-C.
Highly Recommended for Optimal Performance:
- For Macs: A USB C to USB A cable.
- For PCs: An Ethernet cable.
This guide assumes you have a primary Mac or Windows computer with at least one available USB-C port.
Most modern devices come equipped with USB-C, which is why it’s recommended.
Setting Up Your iMac as a Display: Important Steps
Step 1: Insert Your Luna Display Dongle
To begin, take your Luna Display dongle and connect it to your primary Mac or PC—the computer you wish to use with your iMac as a display.
The dongle needs to be inserted into a USB-C port that supports Thunderbolt or DisplayPort. All USB-C ports on Macs are compatible with these standards, but PCs can be more complicated.
For PCs, ensure you plug it into a USB-C port marked with a Thunderbolt or DisplayPort icon. Refer to the chart below for guidance.
Supported USB-C Ports
Step 2: Link Your iMac to Your Computer with a Cable
Although Luna Display offers Wi-Fi connectivity, I highly recommend using a wired connection for the best results when using your iMac as a display.
Running a 5K iMac as a monitor requires substantial bandwidth, so a cable connection will provide the most reliable and consistent performance.
The method for connecting your iMac varies depending on whether you are using a Mac or a PC.
Connecting Your iMac to Another Mac with a Cable
I suggest linking your iMac to your primary Mac with a USB cable—this is my usual setup.
If your iMac is an older model, you will need a USB-C to USB-A cable, which I use with my 2015 iMac and my 2021 M1 MacBook Pro.
If your iMac is more recent and has USB-C ports, opt for a USB-C to USB-C cable. Most users of this guide will likely have older iMacs requiring the USB-C to USB-A option.
After obtaining the correct cable, connect one end to the back of your iMac and the other end to the USB port on your primary Mac.
Connecting Your iMac to a PC with a Cable
Unfortunately, Windows does not support USB cable connections as robustly. Therefore, I recommend using an Ethernet cable for optimal performance.
Any compatible Ethernet crossover cable should work well; here’s a budget-friendly option from Amazon that I recommend.
Connect one end of the Ethernet cable to the iMac’s Ethernet port and the other end directly into your PC’s Ethernet port.
Step 3: Download and Install the Software
With all the hardware connected, the next step is to install the required software on your devices:
Luna Display for Primary Device
On your primary Mac or PC, download and open the Luna Display app.
Luna Secondary for iMac
Then, on your iMac, download and run the Luna Secondary app. You can find the downloads available here.
Step 4: Start Using Your iMac as a Monitor!
At this stage, your iMac and primary computer should automatically recognize each other, and your iMac should now function as a monitor.
There are some other settings you might want to change. I really recommend turning on Retina Resolution so the picture is sharp.
That’s it! 😄 Enjoy the beautiful 5K picture on your iMac as a screen for your Mac or PC!
If you need help with making it work better or fixing problems, please see the FAQs below.
Get your Luna today!
Understanding Luna Display’s Constraints
Like any technology, Luna Display has its limitations and may not be suitable for high-motion applications. For instance, it’s not ideal for gaming or video editing tasks.
Since Luna Display transmits a 5K resolution through a USB connection, you may experience temporary pixelation during rapid motion on-screen, such as video playback or swiftly moving windows.
Personally, this has not been an issue for me, as I primarily use my iMac for activities like audio playback, messaging, and document editing.
Continue reading for additional tips to enhance performance…
Suggestions for Optimal Usage
Note: Some of these tips are applicable only for Mac users. We aim to introduce similar options for our PC software in the future.
If your iMac isn’t delivering the performance you expect as a monitor, there are several settings you can adjust.
Your choices will depend on whether you prefer a sharp display with slower motion or quicker motion with a bit of pixelation.
- For the fastest motion, adjust the resolution.
- For the clearest image, modify the refresh rate.
- If these options don’t meet your needs, you can override the Luna Display settings with manual rate control.
Adjusting Resolution
The easiest way to change the resolution on your Luna Display is by using the “Retina Resolution” toggle that appears after establishing the connection.
Turning off the Retina Resolution can lead to increased pixelation but offers a much quicker response time on your iMac.
Adjusting Refresh Rate
Available only on the primary Mac app
To modify the refresh rate in the Luna Display app, navigate to the menu and select File > Settings.
A settings window will open. Click on Luna Display at the top of the window:
At the bottom, you’ll find a drop-down menu for the Max Refresh Rate. The default setting is 60Hz, but you can try lowering it to 45Hz or 30Hz for a clearer, though slower, display.
After making this adjustment, you will need to close the Luna app and reopen it.
Adjusting Rate Control
Available only on the primary Mac app
This is the best way, and it works better with a wired connection. To change the rate control, hold down Option and choose File > Settings in the main Luna Display app.
A settings window will show up with a Debug option at the top.
In Debug settings, change rate control to Manual and move the slider to the right to use more bandwidth.
This changes right away, so you can use your iMac as a screen and adjust the setting until it’s right.
When you use more bandwidth, the picture will be clearer, but it might take longer to show changes depending on your connection and computer.
