That's partly because your family room may be brighter than mine, and partly because there's a big difference between the image being bright enough to give you vibrant color and good contrast and it being merely bright enough so the image isn't hopelessly washed out. Recommendations for ambient light viewing have even greater variation. I've found that when I set up a projector for testing in a dark room by subjectively judging it for a balance of good contrast and comfortable brightness for viewing, I typically wind up at the high end of that range.

That 16 ft-L recommendation is derived from the Society of Motion Picture and Television Engineers (SMPTE), which defines a target of 16 ft-L but actually allows a range of 12 ft-L to 22 ft-L. For a dark room, for example, the most common brightness recommendation is 16 foot-lamberts (ft-L), though I've seen suggestions as high as 30 to 40 ft-L. But as with screen size, the best brightness is also partly a matter of personal taste. You can also find competing rules of thumb for best image brightness for different lighting conditions.

If you start with the rule that Distance = ScreenDiagonal / 0.84, for example, the ScreenDiagonal = Distance X 0.84. Insist on being in the middle row? Use a ratio in the middle of the range.Īlso keep in mind that if you're trying to find the right size screen for a room that already has a couch or other seating in place, so you already know the distance, you'll want to flip the equation around to solve for screen size. Prefer the front row? Pick the ratio that gives the bigger screen. If you like sitting towards the back of the theater when you go to the movies, pick a seating-distance-to-screen-size ratio in the recommended range that gives you a smaller screen. But if you're trying to find the right screen size to watch from a couch in your family room, personal preference matters more. The ranges these formulas give you are most useful for choosing a screen size in a room with multiple rows for seating, since they'll tell you where the front and back rows should be.

Other sites give rules of thumb in terms of the height or the width of the screen, telling you to sit no closer than two times the width and no farther than five times the width, for example, though five times is a little far for my taste. Either approach-multiplication or division-will give you left and right viewing angles for the image of roughly 30 to 40 degrees, which is the usual recommended range. Beyond that, if you search the Web, you'll turn up several competing rules of thumb for the ideal seating distance for any given screen size.Īmong the most common suggestions are to multiply the diagonal measurement of the screen by 1.6, 1.5, or 1.2 times to get the best seating distance, or divide the diagonal measurement by 0.6 or 0.84.

Indeed, ProjectorCentral's Paul Vail discussed the issue in a Q&A column answering the question, ' How Do I Calculate Screen Size and Seating Distance for My Home Theater?'. If not, you'll probably find it helpful to at least touch on those two steps first.ĭeciding on screen size is worth an article of its own. If you already know the screen size and image brightness you want, you can skip to the section on calculating lumens. When it comes to calculating the lumens you need, you can replace most of the arithmetic with a simple look-up table, which you'll find at the end of this article.Ĭalculating your lumen needs for a particular screen size and lighting doesn't have to be so hard. There's not much you can do about most of these complications, but in this article I'll address one in particular. Then there's the math part of it to negotiate. Unfortunately, it's not so simple in practice, with all sorts of ifs, ands, and buts to account for.

Start with the screen size and the image brightness you need, and then calculate how many lumens it will take to give you that desired image brightness.

How bright a projector you need to light up a screen-whether in a dark room with controlled lighting or in a family room or conference room with window light that changes throughout the day-is easy to determine, in principle at least.

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