As 4K displays are now coming out, a common debate between people online has been about the benefits of 4K compared to HD in a normal viewing environment. Many people will say that 4K looks amazingly sharp and it's impossible not to see the difference, but many others will say that in a regular living room, with a regular sized screen, you really won't see much of a difference.
Update July 3rd, 2013: Read more about HiDPI and 4K Display use cases and benefits. My new article compares smartphones, tablets, laptops, monitors, TVs, and projectors to see where high-resolution provides the most visible benefit.
December 1, 2014: Revised text as 4K/UHD TVs are now available everywhere
November 27, 2015: Updated links and comparisons
Most people who have seen 4K to this point see it at stores that have dedicated displays for it, and not at home. Many times these are setup to only allow you to be so far away from the screen, which makes 4K look great, as it really does look amazing from 3' away. They also use special content to show off 4K, as the main 4K sources right now are streaming services like Netflix or Amazon and custom sources from Sony and Samsung. Since Netflix is unreliable for a showroom floor and most companies don't want to use a media player from a different company, you see custom demo loops that are nothing like what you will see at home.
Now that you can get a 43" 4K TV from Vizio for around $500 UltraHD TVs are mainstream. Since most manufacturers are making their top-of-the-line sets 4K, those who want all the best features have no choice but to go with 4K at this point. Plasma no longer exists, and OLED is still relatively expensive, so you are almost certainly purchasing an LCD. If you're looking for a TV that isn't top-of-the-line, will you see a difference with 4K in your house, or should you invest your money on different features or just spend less?
In 2015 the single best looking TV I reviewed was the 1080p LG 55EG9100 OLED. Even when compared to high dynamic range and wide color gamut displays like the Samsung UN55JS9000 the LG won out because of it's infinite contrast range. A $1,200 55" TV like the Samsung JU7100 or 60" Vizio M-Series offers a better value and higher resolution, but I'd still pick the LG over those even though it's curved.
In 2016 as high dynamic range and wide color gamut material appears on UltraHD Blu-ray, high-end 4K sets will start to have a bigger benefit. This is not because those TVs have more pixels, but because those pixels can go brighter and display more colors than the pixels on a 1080p display. If you gave these features to a 1080p display like the LG OLED (which you can on the $3,000 UltraHD LG 55EF9500) then you'd see even more benefit. Better quality pixels will make a more visible difference than just having more pixels will.
There is a chart from Carlton Bale available that shows when you might be able to see the difference with 4K compared to 1080p or 720p, but I decided to make my own 4K calculator that gives you just a little more detail. Using this you can enter your screen size, your distance from the screen, and your vision to generate some numbers for you. The information this will provide you is:
- The Pixels Per Inch for 480p, 1080p, and 4K signals based on the screen size.
- The maximum resolution that you can discern with your vision based on the distance from the display
- The ideal 4K screen size for your distance, which is the smallest screen at which point you can resolve all the pixels
- The ideal distance from a 4K display of your specified size, which is how close you need to sit to resolve every pixel
- The amount of extra resolution that would be visible on a 4K display compared to a 1080p display based on your screen size and distance. The maximum amount would be 300%, and the minimum is 0%
I've also created a chart, seen below, that gives you a quick glance to see what the ideal viewing distance is for a 16:9 display based on size and resolution. This is based on 20/20 vision, and the viewing range for each resolution is the distance you can sit from that TV and see more detail than a lower resolution, and are not close enough to see the extra detail in a higher resolution screen. So with a 50" 1080p display, if you are closer than 9'9" you will see more detail than a 720p display, but if you are more than 6'6" away, you couldn't see any more detail on a 4K display.
This calculator does make assumptions about vision and arc minutes, but those that I talked to said this was as good of an assumption to make for human vision as anything else. If you think that it is off, you can easily adjust the vision to 20/15 or 20/10 to make it more accurate to you. This also will let you calculate for devices like cell phones and tablets, that will often be placed much closer to your face, to compare them to a 4K display that is much further away. One more assumption is that you have a 16x9 screen, though other screen ratios may be supported in the future.
Many reviewers have tried to compare 4K to 1080p to see if they notice a difference. David Katzmaier pulled in a panel and showed them the same content on 4K streaming from Netflix and 1080p Blu-ray and none of the people could pick out the 4K display. At the same time, HDTVTest did a similar test using 1080p compared to 4K, but they used their own custom content instead of streaming content. In their testing people do notice the difference from a reasonable distance, though unless you are shooting you own 4K content you can't test this yourself.
I talked to other reviewers who tested projectors, being able to instantly switch between a Sony 4K projector and a JVC X700R on a 120" screen. They could barely notice the difference with the 4K resolution using content directly from a RED 4K camera. Even when they did notice, they preferred the JVC image because it had better blacks and a better contrast ratio, and the eye notices that more than resolution. With any display, resolution is only a single factor in how good a display looks. Knowing how much you might see that increased resolution can help you decide what TV will best work for you.
Hopefully this will help you to determine if you will see much benefit from 4K in your situation, as well as making it easier to compare devices like a cell phone or tablet that you hold very close to your face to a TV that likely sits across the room from you.