Luna Display alternative: use a Mac as a second display without a dongle
Luna Display is a small hardware adapter from Astropad that turns an iPad or another Mac into a second display. If you are looking for an alternative because you want to use an iMac or a MacBook as a display for another Mac, this page compares Luna Display with DisplayBridge, the app I develop.
Every Luna Display fact on this page comes from Astropad's own shop, help center and blog, checked on 11 October 2026, and the table also shows where Luna is the better choice.
In short: for a 5K iMac from 2017 or later and a Mac with Thunderbolt, DisplayBridge gives you full 5K at 60 Hz, uncompressed, with sound, for $29. Luna Display is the better choice for an iPad, a Windows PC, a wireless setup, or older Macs that DisplayBridge doesn't support.
Comparison: Luna Display vs. DisplayBridge
Green: the better option in that row · Red: the worse option · No color: not comparable
| Luna Display | DisplayBridge | |
|---|---|---|
| Price | $89.99 for the hardware adapter, paid once, no subscription | $29 license, paid once, for the Mac you work on. Plus a Thunderbolt cable from about $10 if you don't have one |
| Extra hardware | An adapter that must be plugged directly into a USB-C or HDMI port of the main computer (no hubs or adapters). It counts as an external display, so on Macs that support only one external display it takes that slot | None. Only the Thunderbolt cable between the two Macs |
| Picture | Compressed with Astropad's own codec. During fast motion the picture can briefly turn pixelated, according to Astropad's blog | Uncompressed. Every pixel arrives exactly as your Mac drew it |
| 5K iMac as the display | 5K at 45 Hz or 30 Hz; 60 Hz only at 4K. 5K needs the USB-C adapter and macOS Big Sur or later | Full 5K at 60 Hz |
| Sound on the second Mac | No. Sound only plays on the main computer | Yes. The Mac's sound plays through the iMac's speakers, over the same cable |
| What it is meant for | Astropad recommends it as a side screen for content that doesn't change often, and not for gaming or video playback | A full-time second monitor; scrolling and moving windows stay sharp |
| Delay | 1–4 ms over a cable, 7–25 ms over WiFi, according to Astropad. Astropad doesn't say what the number includes | About 20 ms from the moment your Mac captures a frame until the iMac shows it; roughly 10 ms more than a directly connected monitor |
| Connection | WiFi, a direct peer-to-peer connection, or a USB, Ethernet or Thunderbolt cable | A Thunderbolt cable or a 40 Gbit/s USB-C cable (USB4) only |
| Macs that can be the display | Any Mac from 2011 or later on macOS 10.13 High Sierra or newer | Macs with Thunderbolt 3 or 4 on macOS 13 Ventura or newer, for example a 5K iMac from 2017 or later |
| Main computer | A Mac with USB-C, or a Windows PC | A Mac with Thunderbolt 3 or 4 on macOS 13 Ventura or newer |
| iPad as the display | Yes, with touch and Apple Pencil support | No |
| Trying it before you pay | No trial. You can return it within 30 days of delivery if you bought it on Astropad's website; the return shipping is deducted from the refund (US) or paid by you (EU/UK) | Yes: a free 7-day trial with all features, no account needed |
Luna Display facts from Astropad's shop page, its help center articles on system requirements, 4K and 5K resolutions, audio, latency, external display limits and returns, and its iMac guide. All checked on 11 October 2026.
What Luna Display is and how it works
Luna Display is made by Astropad, a small company founded in 2013 by two former Apple engineers, and it has been on sale since 2017. It consists of a small adapter for the USB-C or HDMI port of your main computer, plus free apps for both devices. The adapter makes your main computer believe that a real monitor is attached. The Luna software then compresses that picture and sends it to the second device: over WiFi, over a direct peer-to-peer connection, or over a USB, Ethernet or Thunderbolt cable.
The second device can be an iPad, with touch and Apple Pencil support, or a Mac from 2011 or later. The main computer can be a Mac with USB-C or a Windows PC. Luna Display costs $89.99, once, with no subscription. That flexibility is its real strength, and for some setups it is the only product that does the job.
Where DisplayBridge is the better choice
For one specific job, using an iMac or another Mac as a display for your Mac over a cable, DisplayBridge does better on the things you notice every day.
Full 5K at 60 Hz, without compression
According to Astropad's own resolution article, Luna Display shows a 5K iMac at 45 Hz or 30 Hz when the main computer is a Mac; 60 Hz is only available at 4K. 5K also needs the USB-C version of the adapter and macOS Big Sur or later on the iMac. The picture is compressed with Astropad's own codec. On Astropad's blog, its co-founder writes that with fast motion, such as video or quickly dragging a window, the picture can briefly turn pixelated before it becomes sharp, and that he would not recommend Luna for gaming or video editing.
DisplayBridge sends every frame uncompressed, at the iMac's full 5120 × 2880 resolution and 60 Hz. Text, scrolling and moving windows look exactly as they do on a normal monitor, because the iMac receives exactly the pixels your Mac drew.
Sound on the iMac's speakers
Luna Display does not send audio to the second Mac; Astropad says the sound only plays on the main computer. DisplayBridge sends the sound over the same Thunderbolt cable, so the iMac's speakers play your Mac's audio. You can also keep the sound on your own speakers, or play it on both.
No adapter, and a third of the price
DisplayBridge costs $29, once, for the Mac you work on; the iMac that shows the picture never needs a license. Luna Display costs $89.99. Its adapter has to be plugged directly into a port of your main computer, without a hub or an adapter in between. Because it acts like an external monitor, it also counts against your Mac's external display limit: on a Mac that supports only one external display, such as an M1 MacBook Air, Luna takes that one slot. DisplayBridge needs no hardware except the Thunderbolt cable.
A free trial instead of a return
DisplayBridge has a free 7-day trial with all features and no account. You can test it on your own Macs and pay only if it works for you. Luna Display has no trial: you buy the adapter, wait for it to arrive (Astropad quotes 14 to 21 business days for standard international shipping), and if it doesn't work for you, you can return it within 30 days of delivery. The return shipping is deducted from the refund in the US, and paid by you in the EU and the UK.
Where Luna Display is the better choice
DisplayBridge does one thing: it connects two Macs over Thunderbolt. Luna Display is the better choice if any of these apply to you:
- You want to use an iPad as a display. Luna supports touch and the Apple Pencil. DisplayBridge doesn't work with iPads at all. (Apple's free Sidecar is also worth a look for this.)
- Your main computer is a Windows PC. DisplayBridge only works between Macs.
- You need a wireless connection. Luna works over WiFi and peer-to-peer. DisplayBridge needs a Thunderbolt or 40 Gbit/s USB-C cable, because an uncompressed 5K picture needs about 10 Gbit/s, far more than WiFi can carry.
- Your Macs are too old for DisplayBridge. Luna supports any Mac from 2011 or later on macOS 10.13 as the display, including the 2014 and 2015 5K iMacs. DisplayBridge needs Thunderbolt 3 and macOS 13 Ventura on both Macs, which in practice means an iMac from 2017 or later.
Why the delay numbers can't be compared
Astropad states a delay of 1–4 ms over a cable and 7–25 ms over WiFi (its shop page also mentions 16–32 ms over WiFi). The number comes from Luna's own connection graph, and Astropad doesn't say which steps it includes. It can't be the full time from your action to the picture on the screen: a 60 Hz screen alone needs about 8 ms to redraw down to its middle.
DisplayBridge shows about 20 ms in the app, measured from the moment your Mac captures a frame until the iMac shows it. That is roughly 10 ms more than a directly connected monitor, which is unnoticeable in everyday use. Because the two numbers measure different things, the table leaves this row uncolored. The fair way to compare is to try both on your own Macs.
How DisplayBridge works
You install DisplayBridge on both Macs, connect them with a Thunderbolt cable, and click Connect on the Mac you work on. A few seconds later, the iMac shows up in System Settings as a second display of your Mac, and you use it like any external monitor. The video below is a recording without cuts:
What you need:
- Two Macs on macOS 13 Ventura or later with Thunderbolt 3 or 4: for example a 5K iMac from 2017, 2019 or 2020, an iMac Pro, a MacBook Pro or Air, a Mac mini or a Mac Studio.
- A Thunderbolt 3, Thunderbolt 4 or USB4 cable. A normal USB-C charging cable looks the same but does not work. Look for the lightning symbol on the plug, or "40 Gb/s" on the packaging.
- One license for the Mac you work on: $29, paid once, after the free 7-day trial.
The setup guide explains the two macOS permissions the app asks for when you open it for the first time, and the six-minute setup video on YouTube shows the whole process on my own iMac and MacBook.
Other Luna Display alternatives
- Sidecar (free, built into macOS): uses an iPad as a second display for a Mac. It cannot use a Mac as the display.
- AirPlay to Mac (free, built into macOS): wireless, with a compressed picture. Only newer Macs can receive it; for iMacs, that means a 2019 or newer model or an iMac Pro. My Target Display Mode guide compares it with DisplayBridge.
- Duet Display: works with iPads, Android tablets, Windows PCs and Macs, wired or wireless, as a subscription. The picture is compressed.
- A hardware conversion kit: replaces the iMac's logic board with a driver board, so any computer or game console can use it as a monitor. The iMac stops being a computer. Everything about it is in my conversion kit guide.
The comparison page puts all of these side by side.
Conclusion: which one should you choose?
If you want to use a 5K iMac from 2017 or later, or another Mac with Thunderbolt, as a display for your Mac, and a cable is fine for you, DisplayBridge is the better choice: full 5K at 60 Hz, uncompressed, with sound, no adapter, and $29 instead of $89.99.
Luna Display is the better choice if the display is an iPad, your main computer is a Windows PC, you need it to be wireless, or your Macs are too old for DisplayBridge.
If you have two Macs with Thunderbolt, the easiest way to decide is to download the free DisplayBridge trial and test it on your own setup for seven days.
Questions about this
Is there a Luna Display alternative without a dongle?
Yes. DisplayBridge uses one Mac as a display for another with only a Thunderbolt cable and an app on both Macs; there is no adapter. For an iPad as the display, Apple's Sidecar is built into macOS. AirPlay to Mac also needs no extra hardware, but it is wireless and compresses the picture.
Is there a free Luna Display alternative?
Apple's Sidecar (an iPad as the display) and AirPlay to Mac (wireless; for iMacs, a 2019 or newer model or an iMac Pro as the display) are free and built into macOS. Both compress the picture, and neither drives a 5K iMac at its full resolution over a cable. DisplayBridge is not free, but you can try it for seven days at no cost; after that it costs 29 dollars once.
Does Luna Display support 5K at 60 Hz?
No. According to Astropad's own help center, Luna Display supports 5K at 45 Hz or 30 Hz on a Mac and 5K at 30 Hz on a PC; 60 Hz is available up to 4K. 5K also requires the USB-C version of the adapter and macOS Big Sur or later. DisplayBridge drives a 5K iMac at full 5K and 60 Hz.
Does Luna Display play sound on the second Mac?
No. Astropad states that Luna Display does not stream audio to the iPad or second Mac; the sound only plays on the main computer. DisplayBridge sends the sound over the Thunderbolt cable, so the iMac's speakers play your Mac's audio.
What is the difference between Luna Display and Sidecar?
Sidecar is Apple's free, built-in way to use an iPad as a second display for a Mac. It cannot use a Mac as the display. Luna Display works with an iPad too, but also with a Mac as the display and with a Windows PC as the main computer, and it needs its 89.99-dollar adapter.
Can I use DisplayBridge with an iPad or a Windows PC?
No. DisplayBridge only connects two Macs. For an iPad as the display, use Sidecar or Luna Display. For a Windows PC as the main computer, Luna Display and Duet Display are options.
Which iMacs work with Luna Display, and which with DisplayBridge?
Luna Display supports any Mac from 2011 or later running macOS 10.13 High Sierra or newer as the display, including the 2014 and 2015 5K iMacs. DisplayBridge needs Thunderbolt 3 and macOS 13 Ventura on both Macs, which means a 5K iMac from 2017, 2019 or 2020, or an iMac Pro.