SecondGlow

Use your 5K iMac as an external monitor.

For your newer Mac. Two small apps and one USB cable.

Launching soon · 7-day free trial · $79 once

Hi, I’m Jakub.

I use SecondGlow every day. I got to keep my perfectly good 5K iMac and use it with my faster MacBook. Plug in the cable and it’s just a monitor.

Apple never made that possible, so I built it.

Jakub Chalmovsky · chalmovsky.com

How it works

  1. Host on your Mac.
  2. Viewer on your iMac. It’s free.
  3. Plug in a USB-C to USB-A USB 3 cable. That’s it.
Native 5K
Full 5120 × 2880. Never scaled down.
Mirror or extend
Like any external display.
Sharp and smooth
Crisp text, and ~50–60 fps full-screen video over USB 3.
Brightness keys
Your keyboard dims and brightens the iMac.
Just plug in
The picture appears when you connect. The iMac sleeps when you don’t.
Private
Wired and encrypted. No internet, no account.

Tested on

Each with a 27-inch 5K iMac (2015) on macOS 12 Monterey, USB-C to USB-A USB 3 cable. You need an Apple silicon Mac on macOS 13 or later, and a 27-inch 5K iMac (2015–2020) on macOS 11 or later.

Pricing

$79once, tax included

Questions

Isn’t this what Target Display Mode did?

Yes. Apple dropped it before the 5K iMac came out. SecondGlow brings it back in software: your Mac sends the picture over the cable and the iMac shows it.

Is the picture lossless?

Yes and no. It’s always full 5K, never scaled down. To fit 5K through a USB cable the picture is lightly compressed, so it isn’t pixel-perfect for colour-critical work. Day to day you won’t see a difference unless you have the most trained eye there is. I use it every day and never noticed.

What about Thunderbolt?

It’s coming, as a free update. USB 3 already works great, so you don’t need a new cable. Thunderbolt will just make it even better if you have one.

Can I use the iMac’s keyboard, mouse or speakers?

No, just like any monitor. The iMac shows your Mac’s screen; your keyboard, mouse and sound stay with your Mac.

Does the iMac need to be on?

Yes, it runs the free Viewer app. Turn on automatic login and it comes back as a monitor by itself after a restart.

Is it private?

Yes. The picture only travels over the cable between your two Macs, encrypted, never over the internet. No analytics, no account. I make SecondGlow myself, and you can write to me personally at support@secondglow.app. I want you to be happy with your screen.

My setup isn’t on the tested list.

Try it free for 7 days. I can’t test every combination, so if you’re the first to try a new setup and tell me how it went, you may get a discount.