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Acer K138ST Projector Review – Performance

Posted on December 19, 2017 by Nikki Zelinger

Acer K138ST Projector Review – Performance: Brightness, Display Input Lag, Audible Noise


Picture ModeLumens

Brightness is where nearly all pocket projectors fall short. In fact, most projectors - even larger, more expensive ones - measure up to 25% below claim. The Acer K138ST claimed 800 lumens, which it did not meet. In its brightest mode, Standard, it measured 576 lumens. That's bright enough for a fully darkened room, to be sure, and enough for a room that only has a bit of ambient light leaking through the windows. That is - lights off, shades drawn.

Personally, that's how I watch everything, even on my own projector which has about 2000 more lumens in its brightest mode. So, let's say you get this Acer and it turns out you have more ambient light than you had thought. As mentioned on the previous page, you can get blackout curtains from Amazon for something like $20, and a curtain rod, with your total being well under $50. All you'd need to do is hang up those curtains and draw them whenever it's time to play. That's what I do - my living room has this giant window that leaks light coming from the sun (of course) but also light being reflected from the white garage door across the way. I quickly tired of that game and got the blackout curtains - best decision, hands down.

Back to the measurements - I was surprised that Standard was the brightest mode, rather than Bright mode, which measured at 542 lumens. Now, all the modes are pretty much the same in terms of lumen count. They all fall in the 500 range, with each mode differing by just a few lumens. Movie mode and Game mode both measured at 535 lumens, and Picture mode, its best mode, coming in at 532. As for ECO mode - Standard measured at 514 lumens when running in ECO. All other measurements were taken at full power.

You can see that no matter what mode you're in, you're pretty much good to go. I took the photos for this review with the curtains drawn and light leaking in from my kitchen window (I will be installing blackout curtains there, too, as well as every other room in my house - they're awesome), and that extra light didn't ruin the picture. Alternatively, if you're not into installing blackout curtains and have a lot of ambient light, see our Summary Page where I compare this projector to the AAXA M6, which has more lumens.

Display Input Lag

This projector’s got game! The Acer K138ST has an astoundingly low input lag of 16.8 ms. By comparison, my Epson Home Cinema 5040UB, a $2,699 1080p pixel shifter, has 30.9 ms. That’s considered to be good, with up to 50 ms being acceptable. 16.8 ms is about as low as it gets! For reference, at 30 ms, the projector would be one frame behind on 30 fps games, two on 60 fps games. So, the K138ST will be just about half a frame behind on games that run at 30 fps, one frame behind on those 60 fps games. Translation? Lag will be virtually undetectable.

And that it was. Being a frame or so behind, it’s difficult to notice any sort of lag. In fact, game lag is much more noticeable and occurs more often than input lag at these speeds. I played Star Wars Battlefront 2 online, Skyrim and the remastered Final Fantasy XII Zodiac Age on the Acer K138ST with no problems – in fact, it was a highly enjoyable experience. That the input lag is so low is a real plus for those competitive types that are playing Hardcore mode or accumulative points games on Call of Duty WWII and similar games, where any sort of lag can mean utter defeat.

I would recommend the Acer K138ST for both casual and serious gamers, if the lower HD resolution is not an issue. I personally am a resolution junky (hence my choice of the 4K capable HC5040UB projector), so 720p just won’t cut it for me, especially when playing these games with next-gen graphics. However, the projector is still plenty sharp, and you’ll be hard pressed to find another gaming projector at this price point. It’s not the only one, but that low input lag is indeed a rare commodity.

Audible Noise

The Acer K138ST is exceptionally quiet as compared to the AAXA M5 and AAXA M6 I reviewed. Those claimed to have the same level of fan noise, but they are definitely much louder. The K138ST's fan runs at 33db at full power - that's just about the same as my Epson HC5040UB, which I can only hear if the volume is turned really, really  low. The Acer K138ST is a short throw, as mentioned multiple times, which means that it will be positioned in front of your seating area and you are more likely to hear the fan than if it were on a high rear shelf.

That it is 33db at full power is a real plus, as that's truly excellent for a home entertainment projector, especially in the pocket projector class. In ECO Mode, the projector's fan is rated at 29db - even better. If you use that Bluetooth speaker function, you'll hear the fan even less because you'll have the ability to turn up the volume enough to drown out anything you might still hear.

Up next is our Summary Page, where I - you guessed it - summarize this review and wrap a neat little bow around our discussion of the Acer K138ST. I will also discuss the Acer's direct competition, the AAXA M6, which will go head to head in the upcoming Pocket Projector Comparison Report (2018). Now, onto the final page of this review!

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