Acer K138ST

  • PROS

    Compact. Lightweight. Can project content from a smartphone. Long lamp life. Short throw distance. Comes in soft carrying case.

  • CONS

    Limited connection choices. Rainbow effect in video. Scaling artifacts visible at projector’s native resolution.


    The LED-based Acer K138ST has a relatively short throw distance and can project content from a smartphone via its MHL-enabled HDMI connection.

The Acer K138ST is a highly portable projector for business or casual use, with a relatively short throw for an LED-based model. The addition of an MHL-enabled HDMI port lets it project content from a smartphone. Video quality isn’t great, however, both due to posterization and a considerable rainbow effect. The InFocus LightPro IN1146, our Editors’ Choice LED projector, shows better video and has more connection choices.

Design and Features

The K138ST is a handsome projector, white with a flat top, curved sides, and rounded corners. It measures 2.3 by 9.4 by 5.8 inches (HWD), making it a little larger than palmtop size and smaller than the InFocus LightPro IN1146. It’s lightweight at 1.7 pounds, and it comes with a soft carrying case.

This DLP-based projector has native WXGA (1,280-by-800) resolution, a rated brightness of 800 ANSI lumens, and a 100,000:1 rated contrast ratio. Its LED light source is rated at 20,000 hours in Normal mode and 30,000 hours in Economy mode, so the bulb should easily last the lifetime of the projector. Its throw ratio of 0.8:1 is at the upper limit of what we would consider a short-throw projector. This lets you place the projector a bit closer to the screen for a given image side than a standard-throw model.

On top of the K138ST is a four-way controller with center button that you can use to access the menu system, as you can also do with the projector’s small remote. Behind the lens is a focus ring. As is the case with most short-throw—and most mini—projectors, it lacks an optical zoom.

One interesting feature is LumiSense, an ambient-light sensor that can adjust the projector’s brightness and color saturation based on local lighting conditions. It can be turned on or off from the projector’s menu.

You can project 3D content with the K138ST, but you’ll need DLP-link active-shutter 3D glasses for each member of your audience. It’s not a great choice for 3D projection, however, as rainbow artifacts are visible in some 3D, as well as 2D, images.


The K138ST has a basic set of inputs, including a VGA port, and an HDMI port, which also supports MHL and lets you project content from your smartphone or tablet. There are also audio-in and audio-out jacks, and a port for a Kensington lock, a good protective measure for such a portable projector. Its USB Type A port is strictly for charging an external device like a phone, as was the case with the Acer C205. In comparison, the InFocus IN1146 adds an SD card slot, and its USB Type A port supports either a USB thumb drive or an optional Wi-Fi dongle.

Data Testing

The projector filled our test screen with an 65-inch image (measured diagonally) when placed a little more than 5 feet away from the projector. In data-image testing using the DisplayMate suite, data-image quality was average for an LED-based DLP projector. Colors were well saturated, but I did notice some purple fringing in a few images.

In some data images, I saw scaling artifacts, which generally appear when there’s a mismatch between the image source’s resolution and a projector’s native resolution. They take the form of extra or thicker lines in patterned fills. This is an issue that the K138ST shares with the InFocus IN1144, the Vivitek Qumi Q6-BU, and all of the other LED-based WXGA projectors we’ve reviewed over the past few years that use a TI DLP chip. In these cases, the artifacts are not due to resolution differences, but to the particular design of these chips and the shape of the pixels. Such artifacts shouldn’t have any effect on images other than those containing patterned fills.

The K138ST’s text quality is typical of an LED projector. In testing, both black text on white and white text on black were easily readable at sizes down to 9 points. I noticed more purple fringing than usual around the text, and within the white letters.

All single-chip DLP projectors are potentially subject to the rainbow effect, which takes the form of little red/green/blue flashes, especially in light areas against dark backgrounds. I noticed rainbow artifacts in several of the K138ST’s images, but they are seldom a significant problem in data images and shouldn’t be an issue here.

Video and Audio Quality

In our video testing, rainbow artifacts were more obvious than is usual for a DLP projector, and would likely be distracting even to people mildly sensitive to the effect. I also noticed some posterization, a tendency for abrupt shifts in color or tone when they should be gradual. Because of these issues, I would limit video use with this projector to short clips, whether YouTube videos or as part of a presentation.

Sound from the K138ST’s twin 3-watt speakers is good for use in a small room. If you turn the volume up more than halfway, you receive an onscreen warning telling you that over-boosting the volume can cause bad sound quality. If you want more volume or better audio, you can connect a set of powered external speakers to the audio-out jack.


The Acer K138ST is compact and easily portable, and it has a relatively short throw for an LED projector, so you can position it close to the screen, and you can also display content from a smartphone attached to its MHL-enabled HDMI port. Its brightness and sound system make it best for use in small rooms, and data-image quality is average, while video is best kept to short clips, mostly because of the rainbow effect. The Editors’Choice InFocus LightPro IN1146 has more connection choices, and more watchable video, with fewer rainbow artifacts, but it lacks the K138ST’s short throw.

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