When playing certain video games, it isn't just every second that counts - it's every millisecond. The difference between "now" and "a fraction of a second from now" can be the difference between victory and defeat. This difference -- the time between when an event occurs and when you see it occur -- is called lag. While lag cannot be eliminated, reducing it is key to a great gaming experience.

Input Lag: What It Is

The term "lag" can refer to any time difference. However, we're primarily concerned with input lag. This is the time difference between when a video signal arrives at your projector and when that picture is displayed on the screen. All digital projectors, regardless of their specifications or intended use, will incur some amount of input lag. That's just the nature of digital video processing -- the projector has to take a stream of ones and zeroes and reconstitute it as an image. When that image isn't in the projector's native resolution, it has to be scaled, and that can add processing time. If you're using advanced features like frame interpolation or smart sharpening, those frames of video must be analyzed in sequence and altered before reaching the screen, which adds processing time. Automatic irises adjust themselves based on the average illumination in a scene, which (you guessed it) adds processing time. In other words, there are a lot of things that can slow down an image in transit.

When lag is particularly bad, you will likely notice that something is wrong. When watching movies or video, you might notice that the sound arrives before the picture does, so people's lips don't match their words, or you hear gun shots in action movies before the character on screen has actually fired. When playing video games, you'll press a button and notice a significant delay before the game responds - or you'll respond to a timed prompt on screen, and despite thinking you've nailed it, you miss your cue.

Input lag is of special importance when working with video games because games are interactive. If you're just watching movies or video and input lag is severe enough to cause lip-synch errors, you can correct it with an audio delay that slows down the audio track until it is in synch with the video. You can't do that with games, though, because games require your input in response to what's shown on the screen. If you delay the audio, it doesn't remove the core problem - you find out about events after they've already happened.

Input Lag: What It Isn't

While input lag gets a lot of attention, it is not the only source of gaming lag. A May 2009 article in Eurogamer called Console Gaming: The Lag Factor revealed that console games can be inherently laggy. In Eurogamer's testing of console games, those running at 60 frames per second had an inherent lag of 67 milliseconds (4 frames), while 30 fps games had a minimum inherent lag of 100 milliseconds (6 frames). That's in addition to any lag added by your display (their testing included a check against a reference CRT monitor -- not perfect, but better than nothing).

This inherent lag is not input lag. It tracks the time difference between a button press and a visual response, while we're concerned with the difference between signal arrival and visual response. The delay between button press and visual feedback is usually called "response time," though it's not uncommon to see the terms "response time" and "input lag" used incorrectly.

There's also the issue of network lag. In multiplayer, the game has to keep track of your actions and the actions of everyone else in the game with you. When that data is delayed or falls out of synchronization, it can be intensely frustrating - but it isn't input lag.

Input Lag: Should You Care?

Here's the short version: if you have to ask, probably not.

Input lag can be an important factor in choosing a projector, but only to a relatively few people. Low input lag is always good; it means that movies and video won't require an audio delay and games will display more quickly. But as discussed above, input lag can be fixed when you're using non-interactive media by adding a simple audio delay circuit. Many A/V receivers, in fact, include such a circuit. If yours doesn't, there are stand-alone devices that will do the job.

So that removes movies and video from the equation, and we're left with gamers. But many games can be played on high-lag projectors without issue, especially if those games don't rely on split-second timing. Casual games, turn-based games, and many console games still feel snappy and responsive on projectors with high input lag, and we often hear from projector owners who think a particularly laggy projector is "just fine" for gaming.

If movies and video don't matter and most games don't matter either, who should care? Those folks who play a lot of games, and whose gaming choices demand super-fast responses: most fighting games and first-person shooters. The other group likely to notice input lag are PC gamers. Purpose-built gaming computers give you more control over the level of video processing applied internally than consoles do, so gamers concerned with maximum speed can reduce the number of pre-rendered frames the graphics card will store in its buffer. You can't do that on a console.

If you play a lot of games with fast-twitch response times, and especially if you play those games on a PC instead of a console, you should pay attention to input lag when it's time to pick a projector. If that doesn't sound like you, but you still want to have a solid gaming experience, read on.

The Limits of Acceptable Lag

Just to be clear: when we talk about input lag, we're talking about very small amounts of time. Lag is measured in milliseconds. One millisecond is one one-thousandth of a second. Therefore, if your game is running at 60 frames per second, each frame takes up 16.67 milliseconds.

In Eurogamer's 2009 tests, they found that the point where most people felt lag became detrimental was 166 milliseconds, or ten frames, of total lag a 60 FPS signal. This includes input lag, but it also includes the native response time of a game, which can be significant. When total lag exceeded 166 milliseconds, test subjects noticed the delay in their actions and felt that it was a hindrance to their performance. Therefore, your entire system needs to be fast enough to stay under this ten-frame limit for total response time.

According to Eurogamer, console games running at 30 frames per second represent the worst-case scenario for input lag. If these games have a minimum lag of 100 ms, your projector needs to add less than 66 ms to the overall response time. The good news is that 66 milliseconds is an easy target, and there are plenty of projectors out there that will hit it -- some of them quite affordable.

We make it a habit to check input lag on every projector that comes into the office, regardless of its intended use. Our testing shows that many inexpensive DLP presentation projectors have about 33 milliseconds of input lag, and many inexpensive LCD projectors stay under 50 milliseconds. If your primary concern is speed but you have a tight budget to work with, you can find a snappy, quick projector for less than $500. It might not be native 1080p, but you can't argue with the price or the speed.

If you're looking for something a little more suited to general home theater, there are some fantastic home theater projectors available that offer native 1080p resolution, excellent contrast and color performance, and highly responsive game modes.

The quickest LCD projectors around are the Epson Powerlite Home Cinema 8350 at 34 milliseconds, Panasonic PT-AR100U and Epson Home Cinema 5030UB at 37 milliseconds, and Panasonic PT-AE8000U at 45 milliseconds. Note that the Epson 5030UB's 37 millisecond reading was obtained with Image Processing set to Fast, which can reduce resolution. Some folks are bothered by the effect, and some types of content are more visibly degraded than others.

The BenQ HT1075 is one of the most popular entry-level projectors on the market, and its 49.7 milliseconds of input lag means it performs well enough to beat our 66 ms benchmark. The Optoma HD26 is faster, at 33 milliseconds, but a slower color wheel and weaker overall performance make the quicker response time into a trade that not everyone will be willing to make. The ViewSonic PJD5555W also measures 33 ms. It's slower color wheel generates some rainbows but color saturation and color accuracy is in general outstanding for a sub-$500 DLP projector.

Slightly faster than these projectors is the Sony VPL-VW350ES at 32 milliseconds. Sony's entry-level native 4K projector retails for $10,000, but it proves that you can have high-end home theater and a snappy, responsive gaming experience without buying two separate projectors. A recent firmware update to the Sony VPL-VW600ES means you should see the same gaming performance on that model as well, though we haven't tested this update.

The quickest projector on the market, at least for the moment, is the Sony VPL-HW40ES. It measures an impressive 24 milliseconds (roughly 1.5 frames). If you read that 24 ms figure and turned up your nose, you might want to consider (though it pains me to say so) a dedicated monitor. The fastest monitors available have input lag of less than 10 milliseconds, while the fastest televisions are slightly slower at 14 ms.

If you can tell the difference between 14 ms and 24 ms, more power to you -- but you already know who you are. Don't go throwing away your existing gear if you've never noticed lag before just because you're now aware that faster displays exist. It's the nature of technology that whatever you purchase will be obsolete in about ten minutes, so you might as well get used to the feeling. And as noted above, the people for whom input lag is an important consideration are a relatively small subset of all projector owners.

Getting The Most From Your Projector

Regardless of which projector you use, there are a few simple things you can do to maximize performance and reduce input lag.

First thing's first: whether you use a console or a computer, connect it directly to the projector. Not all A/V receivers will increase lag time, but none of them will decrease it, either, so there's nothing to be gained from running your console or computer through the receiver first. This might mean that you need to run a separate audio connection and switch sources on your projector when you want to play games, but it also ensures the fastest possible performance.

Whenever possible, you should set your console or computer to use the projector's native resolution. If you feed a 1080p signal to a 1080p projector, for example, the projector has to take one less step before displaying that image on the screen. When that isn't possible (because you're using an older console, for example), try using the projector's "native" or "1:1" aspect ratio setting, if one is available. This should display the lower-resolution signal in the middle of the screen rather than scaling it to fit.

The next step is to enable Game mode if it exists. Many times, but not always, Game mode will offer faster performance by disabling some video processing. It's worth a try in any case. On some projectors, this is a preset image mode (usually called "Game"). On others, it's a separate control called "image processing" or "frame response." Check your user manual if necessary.

After that, remember to minimize image processing. This means you should turn off any added features including smart sharpening, the auto iris or auto lamp brightness, and especially frame interpolation. Frame interpolation can single-handedly add over 100 milliseconds of input lag, so turn it off.

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