There’s a saying about technology that it becomes obsolete as soon as it’s out the retailer’s door.

I don’t know if it’s that bad, but I’ve been waiting to pull the trigger on purchasing a 4K Ultra HD TV because I love movies and what I love even more is watching them on the big screen.

Going to the local movie theater, however, can get expensive quickly at today’s prices, especially if a trip or two is made to the concession stand, not to mention trying to find the time.

Many Americans have instead set up a home theater system, and the centerpiece is a large, flat-screen TV or a video projector that projects images onto a flat surface like a wall or screen.

One of the best times to buy a TV is around the Super Bowl, so fans of the game — or the pricey commercials — can enjoy the experience together as a group.

I was impressed, awestruck (and more than a little envious) the first time I saw a movie on a friend’s 4K Ultra HD TV. The picture was so sharp, so lifelike, that images seemed to be in 3D.

And this wasn’t a movie that I had never seen before. It was a musical that my wife loves and has seen ad nauseum with me willingly and, at other times, with me as a captive of sorts.

So what exactly is a 4K Ultra HD TV? Why are they gaining in popularity, appearing on more sales floors or in newspaper ads as they’ve come down in price and are they really worth it?

If you’re looking to buy a new television, models 50 inches or larger now commonly feature Ultra-High Definition resolution.

“Resolution” refers to the number of pixels that make up the TV picture. A single pixel consists of a tiny dot on the screen that, when combined with other pixels, forms an image a viewer sees.

Depending on the size of the screen, a 4K Ultra HD TV can cost anywhere from $250 dollars to more than $3,000. A 65-inch Ultra 8K HD TV can cost as much as $5,000.

High definition TVs have 720p or 1080p displays, referring to the number of vertical and horizontal lines in the image. A 1080p display offers a sharper image and is known as “full HD.”

Ultra HD uses twice as many horizontal and vertical lines as full HD for even sharper pictures because it has four times as many pixels, which is why many call it “4K TV.”

An Ultra HD or 4K display is one with at least 8 million active pixels. For televisions, that resolution has been standardized to 3,840 by 2,160, or four times as many pixels than in a full HD TV.

Speaking of, there are a few 8K televisions starting to hit the market with more than 33 million pixels for better resolution, but for most — and as of right now — they are prohibitively expensive.

The number of streaming options to enjoy with a 4K Ultra HD TV are growing, with Netflix, Amazon and YouTube among the better known that are now offering some 4K content.

Right now, cable and satellite subscription services offer just a couple of channels of 4K movies or documentaries, and primetime shows on the major networks, such as CBS, are not in 4K.

Ultra HD Blu-ray DVDs were introduced in 2016, and some retailers such as Best Buy do sell them, but they require a Ultra HD Blu-ray player that is sold separately to play that kind of DVD.

Gaming consoles like the PS4 Pro and Xbox One X can also play Ultra HD Blu-ray DVDs, but other gaming consoles such as the Wii cannot, nor can a traditional Blu-ray player or DVD player.