SecondGlowComparison · checked on 13 November 2026
SecondGlow vs OpenDisplay for a 5K iMac
OpenDisplay is free and open source, and it does a lot: iPhones, iPads, Android devices and spare Macs can all be a display for your Mac. SecondGlow does one thing: a 27-inch 5K iMac as a display for an Apple silicon Mac. If OpenDisplay works well enough for you, it costs nothing. Here’s where they differ.
Choose OpenDisplay if you want to pay nothing, have an Intel Mac, want Wi-Fi, or want an iPad or phone as a display too.
Choose SecondGlow if you want your 5K iMac to look and feel like a real monitor: full 5K sharpness, smooth video, one USB cable, connected the moment you plug in.
| SecondGlow | OpenDisplay | |
|---|---|---|
| Price | $39 once, 7-day free trial | Free, open source (GPL-3.0) (source) |
| Your Mac | Apple silicon, macOS Ventura or later | macOS 14 Sonoma or later; Intel Macs can send too (source) |
| The display | Retina iMac, 2015 to 2020 (27-inch 5K or 21.5-inch 4K), macOS Monterey or later | Any Mac on macOS 12 or later, plus iPhone, iPad and Android (source) |
| Connection | One cable: USB-C to USB-A (USB 3) on every 5K iMac, or Thunderbolt on 2017 and later | Wi-Fi, Thunderbolt or USB4, Ethernet, or a USB-C data cable on recent macOS on both Macs. Thunderbolt 2 iMacs need Apple’s adapter (source) |
| How the picture travels | Adaptive quality: lossless when the screen is still, GPU-compressed while it moves | Hardware H.264 or HEVC video, at most 18 Mb/s (source) |
| Full 5K | Native 5120 × 2880 on every 5K iMac | Up to 5120 × 2880 when the iMac decodes HEVC in hardware, “most Intel Macs from 2017 on”; otherwise up to 4096 × 2304 (source) |
| Motion at full 5K | About 50 to 60 fps on full-screen 5K video over USB 3, measured by me | About 30 fps at full sharpness from an M5 Pro, about 23 fps from an M1 Pro; about 58 fps in a softer mode, per its README (source) |
| Sound on the iMac | Yes, on macOS Sonoma 14.2 or later | No (source) |
The frame rates come from each maker’s own measurements, on different Macs and content. They aren’t a side-by-side test.
Where OpenDisplay is better
- It’s free, and open source, so you can read and change the code.
- Many more displays. iPhone, iPad, Android and any Mac on macOS 12 or later, not only the 5K iMac.
- Intel Macs can be the sending Mac.
- Wi-Fi works out of the box, as well as cables.
- Shut down the iMac from the sending Mac over a cable.
Where SecondGlow is better
- Smooth at full sharpness. OpenDisplay is a video stream capped at 18 Mb/s, and its own measurements show about 30 fps at full 5K sharpness. SecondGlow uses the cable’s much larger bandwidth to send a sharp picture instead of video, with adaptive quality that keeps motion smooth; I measure about 50 to 60 fps on full-screen 5K video.
- One plain USB cable, on every 5K iMac. USB-C on your Mac, USB-A on the back of the iMac, including the 2015 model, which has no USB-C or Thunderbolt 3 port.
- Made for this one setup. It connects by itself when you plug in, your Mac sets the iMac’s brightness, and the iMac’s screen goes dark when you unplug.
- Sound through the iMac’s speakers, in step with the picture. OpenDisplay doesn’t play sound.
- A person to write to. Questions come straight to me at support@secondglow.app.
Which should you choose?
Try OpenDisplay first if you want to spend nothing, have an Intel Mac, want Wi-Fi, or want to use an iPad or phone as a display too. If you have an Apple silicon Mac and a 5K iMac and want it sharp and smooth at full 5K over one USB cable, try SecondGlow free for 7 days and compare on your own desk.
Other free options, TargetBridge and Sharp, are in the full guide.
Sources
Checked on 13 November 2026, on each product’s own site. Prices and features change; follow the links for today’s details.