Oh, now you've gone and opened a can of worms there. There is quite a bit to cover on this topic, and although I won't be able to account for all scenarios, hopefully I can give readers a few ideas on how to assess their computer monitor needs. This article presumes that you are someone with low vision who will potentially benefit from a larger monitor, and that you want to increase the size of text and other items on that screen. The settings discussed relate to Windows computers, but the concepts are the same for Mac users.
There are a lot of factors to take into consideration when purchasing a monitor. If you have low vision, two of the first things you should determine before even going to look at screens are your optimal viewing distance and, at that distance, your optimal text height.
We can use Microsoft Wordpad or a similarly featured word processor to do this. To start, your monitor resolution should be at its optimum setting and your computer's DPI Scaling control should be set to 100%. Open your word processor and set your font size to Verdana 14 point and then type a few lines of text. Set the text zoom in your word processor to 100%. If you've followed these guidelines the text you've typed should be about 4 millimeters tall and, objectively speaking, be fairly sharp on screen.
Now, increase the zoom setting in the word processor until the text becomes comfortable for you to read. Note, you should not have changed the font from 14 point to do this. Play with the zoom setting until your text size is as comfortable to view as possible. Notice the distance from the screen to your eyes. People generally optimize this for themselves intuitively based on how their vision works and by what the screen content looks like. Some eyeglass wearers opt to or need to use their glasses while others work without them.
Then, take into account the text height that you've zeroed in on. You can actually take a ruler and measure it if you want to be precise or you can just use a finger as a gauge.
Set those two numbers aside – we're going to need them in a bit. First, here's some relevant terminology.
Screen size - a diagonal measurement in inches of the viewing surface of a monitor. Desktop monitors commonly range in size from 15" up to about 30".
Aspect Ratio – this is a ratio of the long side of the screen relative to the short side. The 4:3 screens that used to be so common a few years back are getting harder to find. 16:9, or wide screen, is a far more common ratio these days for standalone monitors.
Resolution – this is the number of pixels on the monitor, usually represented by pixels in length multiplied by pixels in height – something like 1920x1200 or 640x480.
DPI or Dots Per Inch – This is the number of pixels per linear inch on your screen. For instance, a 24" monitor will generally have a horizontal dimension of about 21" and a resolution of 1920x1200 pixels. Take 1920 and divide by the width of the monitor and we get a DPI of about 92 pixels per inch. By comparison, an iPhone 4s has a screen that measures 3" x 2", a resolution of 960x640 and a whopping DPI of 326.
Now that we understand some terminology, let's go back to your numbers that you worked out. If you've determined that half-inch (1.25 cm) high text and a viewing distance of eight inches (20 cm) works best for you, let's talk about some real world scenarios.
If all you ever want to do is work in your word processor, any monitor will work because as we've seen, we can use the zoom feature in the program to easily scale up the size of our text. Scaling is great because the computer actually redraws the text and adds in extra pixels to the letters, making them look smooth and sharp at whatever size you make them. The problem you may have already noticed is that everything else on the screen has stayed small. In fact, at the optimal resolution and dpi settings, the text labels for the menu items on my word processors are a mere 2.5mm tall. In other words, all is well and good when you're actually typing on screen but you may be in some trouble when you go to save that document because the fonts used outside of the document are so small.
A common first line of defense in this scenario is to use less magnification in the word processor and use a lower screen resolution setting to blow everything on screen up a bit. There are some problems with this approach. When we move below the optimum screen resolution, the computer simply stretches everything to make it fit the size of the screen. This makes everything blurry and depending on the resolution setting, may distort the shape of objects as well. Also, it does not give much of a size advantage. When I lowered my 1920x1200 screen resolution to 1152x864, my problematic word processor menu text went from 2.5mm to just 3mm and it lost sharpness to boot. There are better options.
The next line of defense is to instead adjust the DPI scaling – you may recognize this as the "make text and other items larger or smaller" feature on a windows computer. For my 1920x1200 monitor, I started by changing my DPI scaling from the 'Smaller 100%' option to 'Extra Large 200%'.
Now we're getting somewhere. Seemingly everything is now double in size. My menu fonts are about 5mm in height and they're nice and sharp too. However, although this is a big improvement, remember that you've determined you really need your text to be 1.25cm in height. So, what happens if we go in to the custom settings and use the maximum 500% DPI scaling option? Unfortunately, nothing good. Note: It can be quite difficult to reduce your DPI once you've increased it. Please do not make these changes unless you are comfortable with the process of reversing these settings.
Image Caption: A screen capture of my 24" monitor with my computer set to 500% DPI scaling. Notice the tiny amount of working area and the scroll bar I would need to use to see the right hand side of my line of text.
Back in my word processor, I see that my menu text is a full 1cm in height, just about half an inch. We may not have the 1.25cm there that we've been hoping for but we're entering the ballpark and looking for a hotdog. The problem is that our working area is all but gone now. I can't even fit one full line of my own text in the working area and there's a left/right scroll bar that I'll need to use to read from one end of a line to the other.
If we look around the rest of the computer with these settings enabled, we'll run in to all sort of problems – scroll bars everywhere, buttons inaccessible off the bottom edge of the screen, text bleeding in to adjacent text. In fact, I can't even find the controls I need to change back to a lower DPI setting. Using extreme scaling/DPI settings simply makes a computer unusable visually.
If you instead take the approach of manually adjusting text sizes in various areas of your computer, you will eventually run into the same problem described above if you require significantly large text.
Here's a simple rule, the higher the resolution of a monitor, the more DPI scaling we can get away with before problems start to occur. On my 1920 by 1200 monitor, 200% scaling works well in most cases. If I go much higher than that, I start to run in to problems with essential controls falling off the edge of the screen and I see scroll bars showing up everywhere. If you have an older 1024x768 monitor, you might try 125% scaling but you won't be able to get away with 200%. The new 4K (4000 pixels on the long side) monitors that are coming out may allow for higher than 200% scaling before problems occur.
Here are some points to summarize:
If you require significantly large text, a monitor of a given size with high resolution does not provide a significant advantage over one the same size but with lower resolution (ie: two 24" monitors, one 4K vs. 1920x1200). The 4k monitor simply gives the advantage of making small objects and text sharper.
A larger monitor provides more room to display larger text sizes. However, because so many different font sizes are used throughout a computer, it can be impossible to find a happy medium DPI setting if you need significant magnification.
If we push the DPI/Scaling setting too far ("too far" varies depending on the resolution and size of the screen) everything increases in size but those things crowd too close together. Pushed too far, they overlap or fall of the bottom edge of the screen, making the computer very difficult to use.
If you are someone who requires just a small increase in size of the smaller fonts found throughout a computer, DPI scaling will likely be quite helpful.
If you require significant magnification for those same fonts, you will likely have a much better experience through the use of a screen magnification program. I'll talk about screen magnification in a later post.
So, we've established that DPI scaling can provide a useful small bump in magnification but really isn't a lot of help if you need medium to high levels of magnification. Perhaps you've decided to investigate screen magnification software. In either case, the question remains, how big of a screen should I buy?
Let's return to the numbers we came up with at the beginning of this post. What happens when we look at our half inch high text from eight inches away? If you have a small 15" monitor, that text will be pretty much the same effective size in the middle of the screen as it is at the edges. However, if you trade that for a massive 30" display, you'll find that half inch text may not be readable towards the sides of the screen. It will appear much smaller in size. That's because the sides of that big monitor are so much further away from you than the center. You would likely find yourself doing a lot of chair dancing to see what's on the edges of that screen.
On the other hand, you may instead have determined that two feet is your optimal viewing distance. That 30" monitor will make a lot more sense then.
Simply put, if you sit close to your screen a smaller monitor will make more sense ergonomically.
A word about laptops. If you prefer a close working distance to the screen, laptops can cause some difficulty - you'll find yourself leaning over your hands in order to see the screen well. This can quickly lead to repetitive strain injury in your arms and is terribly hard on your neck and back.
If you've stuck with me all the way to the end, you can see that selecting a monitor can be a bit of a balancing act. Hopefully this information will help you make a selection.