Review of the Luna Display

Like anyone who listens to Mac tech podcasts, I’ve heard about the Luna Display many times, but the only people I’ve heard talk about it are people who are reading ad-copy. I looked around, but did not find many independent reviews, so I thought it might be helpful for others to hear from someone who might have a different perspective to bring, especially since it doesn’t have to fit in a two-minute ad spot.

Let me be clear: that is not to say that I don’t trust the people who read the ads. If I didn’t have faith in their integrity, I wouldn’t be listening to their podcasts. I do not think any of the podcasters that I listen to would say anything untrue or that they didn’t believe. But even the best ad-spots have a major restriction: there is a limited amount of time available, so the ads have to focus on a few important-but-basic points about functionality.

Here’s my “Executive Summary” review: using the Luna Display with my 12.9" iPad Pro feels almost as if I am using macOS as a native iOS app. The speed and responsiveness are great, and it’s straightforward to use. However, there are some important caveats, especially if you are using a smaller iPad, or if you are not using the iPad as a second display for your Mac.

How it was meant to be used vs. how I’m using it

It’s important to remember that the “sales pitch” for the Luna Display is “Turn your iPad into a second display for your Mac.” That’s the primary way that the Luna Display was intended to be used.

I’m not using it that way. I’m using the Luna Display to connect via Wi-Fi to my “headless” Mac mini (a Late 2012 model running at 2.3 GHz with a Core i7 processor and 16 GB of RAM) which is plugged into an Eero on the other side of the house. More specifically, the mini is downstairs, and about three rooms away from where I’m usually seated when using the iPad. There is another Eero in the room I am in, meaning that there is a decent Wi-Fi connect between the two of them, even though they aren’t in the same room.

Once connected, the Luna Display is super-fast. It feels much faster than using VNC over the same Wi-Fi connection. I can type as quickly as I want to, and the display usually has no trouble keeping up. There is occasionally some “pixelating” if I am watching a full-screen iTerm window with many lines of text scrolling past at a fairly quick pace, but it almost always smooths out quickly when the scrolling stops (I’ve seen much worse over VNC). If this is how the Luna Display performs when connected to a 6-year-old Mac mini over Wi-Fi, I can imagine that it’s even better if you are using a newer/faster Mac, especially if you are sitting right next to your Mac and using it. In short, no complaints about the performance.

(Although it is intended to be used wirelessly, you can use Luna Display with a USB connection which is a nice fall-back option to have if you need it. I would expect performance to be stellar, but I haven’t had the need or opportunity to try it out myself.)

Luna Display is not VNC

Before the Luna Display arrived, I assumed that the Luna Display would be primarily an enhancement to VNC. I thought of the Luna Display as a kind of “hardware display accelerator” which would work over VNC. I’m not sure why I thought that, but it was an incorrect assumption.

To get Luna Display working, you need four things:

  1. The hardware “dongle” connected to your Mac, either via USB-C or Mini DisplayPort;
  2. Luna Display software running on your Mac;
  3. Luna Display software running on your iPad;
  4. Both the Mac and the iPad have to be on the same (preferably 5GHz) Wi-Fi network

(n.b. The Luna Display software for Mac and iPad is available at no additional charge.)

The software has to be running on your Mac.

Since the Luna Display is not VNC, it requires its special “helper” app to be running on your Mac, which doesn’t seem like a problem, until you reboot. Then you can’t connect use Luna Display to connect to your Mac because the software isn’t running.

If you are using the Luna Display as a second display, as you can log in using your primary display, and launch the Luna Display app.

However, if you are using the Luna Display as a primary display, you are out of luck after a reboot. You will need another way (such as VNC) to log in to your Mac and launch the Luna Display app. Then you can switch to the Luna Display app on your iPad.

My Mac mini is a “server” which I do not reboot it very often, so this is not a huge issue, but it is something to be aware of. If your Mac is in a secure location, you could set it to log in automatically upon reboot, but that isn’t something that I would generally recommend.

Speaking of the Mac app, I have a few thoughts (read: “complaints”) about it.

My main complaint is that the app runs in the dock, and has to be left running all the time. This is the epitome of an app that ought to run in the menu bar. Its only purpose is to set preferences, which the user only needs if they are going to change where the iPad is in relation to the primary display. Other than that, the app just needs to be running for the iPad app to connect to it.

For some reason, the app window re-appears from time to time in the background, even when I know I have not interacted with it. Since I don’t need to use the app (I’m not using Luna Display as a second display), I created a Keyboard Maestro macro that automatically hides the app immediately any time it is activated.

Hopefully, the developers will add a “menu bar only” option so I can hide it behind Bartender and forget it exists.

The Only Real Problem

The only real problem that I have encountered with using the Luna Display is that sometimes the Luna Display can’t connect, even when the software is running on your Mac.

The initial setup of the Luna Display was very smooth. I tested everything for a few minutes and was very impressed. Then I exited the Luna Display app on my iPad and spent some time doing other things. Awhile later, I relaunched the Luna Display app on my iPad, and it stayed on its initial “Connecting…” screen. I waited, but nothing happened.

A quick VNC to my Mac confirmed that it was still running, as well as the Luna Display app. So why was Luna Display unable to connect? I switched back to the Luna Display app on my iPad, and it connected to my Mac. I hoped this was just a one-time glitch, but it wasn’t. The same issue recurs any time I don’t use the Luna Display app on my iPad for a while. The app will launch, but does not connect. If I make a VNC connection, then switch back to the Luna Display app, and it works. I have tried waiting longer with the Luna Display app running on my iPad, to make sure that I wasn’t being impatient, but sometimes it just will not reconnect until I go through that little VNC dance.

I contacted Luna Display’s support team about this problem, and although they were aware of it, they did not have any solutions.

This seems like something that hopefully can be fixed in a software update, but I’m not a developer, nor do I know what the problem is, so I can’t say that for certain. As of this writing (late December 2018), it is a persistent problem. If you are using the Luna Display as a second display, I suspect this problem will not appear, because when the primary display wakes up, I assume the Luna Display software will also wake up. However, as a primary display, this is a problem that you should know about.

Setting the Energy Saver preferences to “Never” for “Display Sleep” seems to mitigate the problem if it hasn’t been too long since the last connection. The trick is figuring out how long is “too long”.

Someone suggested that using an HDMI dongle on my Mac mini could help Luna Display connect more easily and reliably. I tried it, and can report not only did it not help, but it confused the Luna Display so thoroughly that I had to disconnect the HDMI dongle, reinstall the Luna Display software, and reboot the Mac mini before it resumed working properly. So… yeah. Don’t do that.

A Workaround

After trying to troubleshoot the reconnection problem, I realized that establishing a VNC connection (even without logging in) was enough to “wake” the Mac mini enough for the Luna Display to connect. So as long as the Mac thinks that the display is on (or should be on), then the Luna Display can connect.

So… if the Energy Saver setting isn’t enough, is there something else I can do to tell my Mac that it’s display should always be on? The answer is a resounding yes with caffeinate – a little command-line tool designed to keep your Mac awake while a particular process is running.

One of the things that it can do is simulate user activity. Quoting from man caffeinate:

-u Create an assertion to declare that the user is active. If the display is off, this option turns the display on and prevents the display from going into idle sleep.

Aha! So now we know how to keep the display turned on.

To tell the computer “Keep the display on and the computer ‘active’ for as long as the Luna Display app is running” we can use this command:

caffeinate -u '/Applications/Luna Display'

Obviously, no one wants to run that command every time they want to run Luna Display, or even every time they reboot their Mac. That’s where launchd comes in.

Take a look at this:

That is a .plist file for launchd which will automatically launch the Luna Display app with the caffeinate command. Not only that, but if I accidentally quit the app or it crashes (which it hasn’t, but just in case), launchd will automatically relaunch the app, with the caffeinate command. This makes sense because I always want the Luna Display app to be running anytime I’m logged in.

(Oh, and if you’re worried about what happens when you try to log out or reboot, fear not, that still works fine.)

How to install and use the .plist file

In order for the .plist file to be automatically loaded by launchd, it has to be saved to a specific folder: ~/Library/LaunchAgents/ (where ~ represents your home directory). If the directory does not exist, just create it. The easiest way is with this command in Terminal:

mkdir -p ~/Library/LaunchAgents/

Once you have the directory, download the .plist here and save it to something like ~/Library/LaunchAgents/com.tjluoma.lunadisplay.plist. (The name isn’t important except that it has to end with .plist or else launchd will ignore it.

Once you have it saved, you could log out and log back in, but it’s quicker to just run this command in Terminal:

launchctl load ~/Library/LaunchAgents/com.tjluoma.lunadisplay.plist

If, for some reason, you want to stop the Luna Display app, just run this command:

launchctl unload ~/Library/LaunchAgents/com.tjluoma.lunadisplay.plist

Or just delete the com.tjluoma.lunadisplay.plist file in Finder and then logout / login.

Size Matters

Running the Luna Display with my 12.9" iPad Pro is great. Running the Luna Display with my older 9.7" iPad Pro was not. The speed was still fine, but using a Mac with that screen size/resolution felt very cramped.

Again, this is because I’m using it as a primary display, not a secondary one. If you are using a 9.7" iPad Pro as a second display, I’m guessing it would work just fine, but as a solo screen, I do not think the 9.7" screen gives you enough room to work comfortably.

When I was using VNC, I could get around this by adjusting the screen resolution of the Mac, as long as I was willing to put up with some “letter-boxing.” Luna Display doesn’t do that. Instead, you are stuck with a 4:3 display with not a lot of space. (Well, the other option was to tell the Mac mini to run at 2x, which just made everything look ridiculously small, so that wasn’t practical.)

I don’t have a 10.5" iPad to try, but it’s my opinion that anything smaller than 12.9" would be very cramped to use as a primary display. If I only had the 9.7" iPad, I think I would have just stuck with VNC and sent the Luna Display back. That’s not the fault of the Luna Display, but it is something to be aware of if your use-case is the same as mine but you have a smaller iPad.

Odds and Sods

There are a couple other minor things that I’ve noticed.

First: There’s no way to share your clipboard between the iPad and the Mac, which is something that I do quite frequently with VNC, but Luna Display tech support confirmed there is no way to do this. (I work around this by copying/pasting via a Bear note, which syncs very quickly, but it’s not ideal.)

Secondly, I’ve become accustomed to using a “two-finger tap” to send a “right click” when using VNC to connect to a remote Mac. This doesn’t work with the Luna Display, although their support team suggested it could be added in the future. In the meantime, you have to hold down the Control key and tap, which is completely logical (after all, “right click” on the Mac was originally “control-click”) but I still find myself using the two-finger tap all the time.

Luna Display vs Duet Display

I used to use Duet Display with my MacBook Pro, and it worked very well. However, at that time, Duet was using a wired connection between the Mac and the iPad. That limitation never bothered me, because I wanted my iPad nearby anyway.

However, Duet has since changed, and it now uses AirPlay. As you may know, AirPlay does not have a good reputation for reliability or performance. I think that Duet was essentially forced into that decision due to some changes in macOS, but it’s a compromise.

Duet costs $10 for the iOS app, but the Mac & Windows companion apps are free. Duet has also added two subscription services for some of their more advanced features, including wireless support. Duet “Air” is $20/year, or $25/year to turn it into a “professional drawing tablet.” The Luna Display is a higher initial cost ($80), but it’s a one-time fee. You can try it for two weeks and see if it works, and if it doesn’t, send it back. Duet will cost you $10 to try, and then you can get a 7-day trial of the advanced features if you want to try them out.

Luna Display has a comparison chart between Luna and Duet which highlights what they see as Luna’s advantages, but even keeping that in mind, I think it is fairly indisputable that AirPlay is neither as fast nor as reliable as what Luna Display offers. Unless you want those “professional drawing tablet” features, I think the Luna Display is the better solution.

Update: Duet Display has apparently moved away from using AirPlay, but only for people running the latest version of Mojave. I am sticking with High Sierra (because reasons), so I can’t test this myself, but if you are thinking about Duet vs Luna, it is something to consider. There is a free 7-day trial of Duet’s “Air/Pro” features, so that may be worth checking out.

A Slightly Off-Topic Mini-Rant about iOS

(To be clear: my complaints in this section are not specific to Luna Display. The same problems exist when connecting to a Mac using VNC. “So why include them?” you might ask. Well, I needed to get them off my proverbial chest.)

When you are connected to a remote Mac via VNC or Luna Display, you can quit remote apps with Command+Q (because the iPad has no equivalent of Command+Q for iOS apps) but you can’t use:

  • Command+H to Hide
  • Command+Tab to switch apps
  • Command+Option+D to show/hide the Dock
  • Command+Space to trigger Spotlight (or Alfred, or LaunchBar)

iOS will intercept those keyboard shortcuts because it assumes they were intended for the iPad.

It would be nice if iOS were smart enough to let VNC apps (and Luna Display) send all keyboard shortcuts to the remote computer (users could exit the iPad app by swiping up from the bottom) but I won’t hold my breath waiting for that to happen.

Yes, of course, there are workarounds. I could change the keyboard shortcuts for switching apps, or showing/hiding the Dock and triggering Spotlight/Alfred/LaunchBar.

I could use Keyboard Maestro to remap “Hide” to Option+H because I can’t do that with the built-in macOS tools, unless I wanted to redefine “Hide {Application Name}” for each application, which is obviously insane and impractical.

But the whole reason that iOS uses these keyboard shortcuts is that they are familiar to Mac users, so it’s annoying to have to use workarounds when connecting to a Mac. It would be much easier to change those keyboard shortcuts on iOS and learn new shortcuts on a new platform, but, oh right, you can’t change keyboard shortcuts on iOS – yet? Ever? Maybe someday, but I’d bet it’s a long time before that feature ever comes to iOS, and I would not be shocked if it never does.


Conclusion: Is Luna Display as good as they say on the ads?

Yup. It is. It really is.

If you want to use your iPad as a second display, I can’t imagine anything better.

If you are using Luna Display as a primary display, I think it is a very good tool which has the opportunity to be great if that one issue gets worked out. In fact, with the workaround described above, it has achieved great status for me.

In addition to being impressed with the Luna Display itself, I contacted Luna Display’s customer support several times with questions or feedback and found them to be very responsive. I consider customer service/support to be an essential feature too.

They do offer a 14-day return period, which is plenty of time to test it out and see if it works for you.

If you decide to order one, remember to use one of those promo codes and support your favorite podcast!

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Copyright 2018 Timothy J. Luoma