Equivalent Visibility and The 4/6/8 Rules - Choosing the right Display Size For Each Classroom

Teaching in the Classroom: Schools and Other Educational Institutions Need to Pay More Attention to the Equivalent Visibility Rule in Data/Info Oriented Classrooms

In one sentence: This rule will tell you how large a display you will need to effectively teach in the classroom (or any room for that matter), so that all the students (or others) can see the screen well enough to read and retain the displayed information.

Understand upfront that achieving full equivalent visibility in a classroom is rarely achieved so that everyone is close enough to a large enough display to read everything in the screen.

It accomplishes this working from a simple assumption:

The image at the front of a room needs to be large enough so that the furthest back person viewing it in a room will see the content as appearing as the same size to them, as that same content would be if viewed on their computer while sitting at their desk!

The assumption is, that our eyes are typically about 28” back from a 21” display when placed on one’s desk. In theory, if you can read a small-sized type on your desk monitor, then you should be able to read the same content the “last row.” That rarely happens, but when a room is well designed, a large enough display can allow most in the room to read all the small type, and the rest, close enough to pretty much be able to follow.

Can you read this?

I’ll take a moment to say that as a projector focused reviewer, I have been writing occasionally on this topic for over 20 years. Long before the term Equivalent Visibility was used in a 2015 white paper produced by PKE Consulting (PKE has produced a number of technical White Papers on topics relating to Displays, VolP, Unified Communications and more).

Back in 2016, Epson asked me to take PKE’s White Paper and “translate it” to more of a user-friendly document on Equivalent Visibility. I did that in two articles back in 2016. This is an update, that considers the practicality of achieving E/V or getting “close enough.”

E/V has become even more important in the display purchase decision making process the past couple of years, as large monitors are now competing in some classrooms and workspaces.   This means IT/AV professionals have additional choices to consider.

Conversely, a WXGA projector, mounted with a fixed or pull-down 100 – 120” screen suitable for most K-12 classrooms, can be had for $1,000 to $2,000. Both projectors and monitors will normally require installation, so it can come down to a 100” plus projector, or at today’s prices, a 70” inch monitor. A 100” screen is just over 2X the overall size of a 70” monitor, and can be read as well as a 70” monitor, from almost 50% further back in the room. That should make a real difference in learning – for the folks in the back half of the room.

Having a 90”, 100”, or larger monitor, might work a world of difference compared to a 50”. Consider some of the results of a study on the impact of screen visibility in the classroom:

Back in 2007, a 100” monitor was still six figures! Today though, such a bargain! Planar, for example offers a 98” computer monitors – for a mere $32K (discounted).

So, monitors offer a reasonable alternative to projectors, price wise up to about 70” in size, but if you need larger – and you do, in almost most classrooms for 7^th through 12 grades – a projector is the way to go. (Before, and while children are first learning to read and write, everything is done in large sizes so that a monitor may be viable).

The Bottom Line Cost-Wise: If a room calls for a monitor larger than the 70” – 80” range, the costs are still too prohibitive for schools, and for that reason, projectors will continue to rule for some time yet. 

Today, the concept of Equivalent Visibility is more important than ever for schools. For you to understand why, this is what Equivalent Visibility is all about:

It is a rule that, when effectively used, will help you to determine what size display – projector/screen, or monitor – is needed for different sized classrooms and different seating layouts. And, it is built around the idea that the teacher or presenter is displaying typical “small type “and graphics to the class, rather than typical “PowerPoint” large type/graphics, or other larger imagery (as might be used in the lower grades).

E/V simply goes a step further, than the 4 in 4/6/8. Equivalent Visibility exists in the 4x range, and limits it to the same level of readability as one has on a typical desktop. Much of the range defined as 4X in 4/6/8 defines a monitor size that most students will have trouble reading, whereas with E/V they will be able to read it. As you can see in the chart above – where the 4X calls for a 101” display size in a 20-foot deep room, EV looks for a 149 inch. That difference is basically the same as comparing our first illustration in this article, which compares the sizes of a 65” and 100” display.

In the Good Old Days: Once upon a time, the vast majority of time when teachers (or scientists, or business people), got up in front of a group, they tended to use formal presenting software.  PowerPoint (around since the ‘80s, or, for those with long memories – Harvard Graphics, which was pre-Windows). By the way, low resolution displays were one reason that type sizes had to stay large – let’s face it, 10 or 12-point type really isn’t very readable with an old VGA display 640 x 480. Even an average WUXGA monitor today (not even 4K capable) has 9X the resolution of VGA.

The thing is – in the past, most projected classwork used very large and huge type sizes, rarely smaller than 24 points, and often not smaller than 30 or 36-points. Titles were typically 42 to 60-point type sizes.

For purposes of this article, we will assume that a typical K-12 classroom is about 1,000 square feet. I’ve rounded up slightly, as 960 sq feet, is California’s recommended classroom size.

Equivalent Visibility: Here’s what seating might look like in two different roughly 1,000” sq. foot classrooms, one square, the other deep. The three colored ranges show 4, 6, and 8. E/V, as noted, would make up the closest part of the dark green 4X area (to the display), but not all of the students in the dark green area – the ones furthest back would not be able to easily read content equivalent to a 21” desktop monitor.

In this square room, even using the 4/6/8 rule, you see that about 1/3 of the students can read everything, and the rest can make out just about everything – and follow any discussion on a 100” display size.

In this deep 1,000 sq foot classroom, only the folks in the back row are missing out on most things (on a 100”), but on a 65” inch, over 1/3 can’t make out anything. And only 3 students are roughly close enough to read everything.

In other words, the difference between a 65” and a 100” display can make a huge difference in the amount of learning going on in a classroom, and the larger display is less likely to severely limit the learning of students in the back of the room.

Today, it’s a different world than 25 years ago. Schools and teaching is less about formal presenting, and more about interactivity, and working with all types of documents. In a high school, that might be charts of data in Excel, or reading an article off of the web – projected up on the display, or Word type documents. The point, today, in the classroom students see small type, small objects, probably more than they do any sort of formal “old school” presenting. In a middle school, it might be geometry, or algebra, or history.

Example: If the class is studying the Gettysburg address (which is drastically shorter than this document), Lincoln’s famous speech totals 275 words. Yet, as a typical PowerPoint Presentation, with 36-point type, it would take about 8 pages to display the entire two minute speech, in order to discuss with the class.

First image below: The first paragraph of the speech with 36-point type (typical PowerPoint).

Second Image below: The entire speech on one page, done in 14-point type (slightly larger than standard size), on a single slide.

Now, let’s see who in the class can read what, using 4/6/8 or Equivalent Visibility:

4/6/8 says that 4x is for when you need to be able to see the details, small type of the screen. 6x is you can see most of it, but not all, details missed. Good for video conferencing too.

8x allows you to be furthest back from any size screen, but is generally for watching videos, as small text and details are completely illegible.

Above: A slide with 36-point body type would look like this, and is considered on the small to average size for a PowerPoint presentation. This slide above should be readable from the back of the room.

But, the Gettysburg Address would be at least 4 or 5 slides long, which is fine if the teacher wants to only discuss a sentence or two at a time. But if the class wants to get the overall feel, and all the words, much smaller type is needed to make it fit into one slide:

There is no way, in a normal K-12 classroom (or higher ed) that students anywhere but the front of the room will be able to read this slide above – and this slide uses 14-point type still a couple points on average larger than the average document, email, or spreadsheet type!

Better to present it over one or two pages. The problem? The type will be small enough that only the students in the first couple of rows have a chance to read it.

But if you put it up on your laptop, or desktop, and read it at your normal distance from those screens, it should work out about the same. You won’t be viewing your 13” laptop from 28” inches back, because if you tried to view that laptop at 28” instead of being this easy to read, it would look roughly like this:

A 13” laptop’s equivalent visibility, would make the type this readable!

Instead of this:

A 13” laptop’s equivalent visibility, would make the type this readable!

In today’s education and business worlds, the assumption of only using only large and very large type while teaching or presenting, is mostly a memory of the past. Huddle spaces, classrooms, interactivity, multi-purpose rooms all need to be set up so that learning is effective no matter where the student or listener is relative to the screen and the teacher/presenter, because many of the documents being displayed use small type, or small objects.

The Equivalent Visibility Rule, like the older, better known 4/6/8 rule, is very important in determining effective sizes for displays in rooms, and is more suitable for today’s smaller type and objects presenting including spreadsheets, Word docs, emails, or, for that matter, tens of thousands of pages of classroom content, already available.

If a student (or other person) can clearly read something on their screen at their desk, or on their laptop when it’s on their lap, then they need to be able to read that same information from a seat in a classroom or conference room, or risk failing to learn!

With display sizes under 100” diagonal (4x in a 20-foot deep room), in most classrooms (other than teaching the youngest where everything is done large) the maximum level of comprehension is just not possible or practical.  

Equivalent Visibility should be a goal, in classroom, even if not fully achievable in most cases. It certainly should be attempted in data-driven classes, which would include labs, and smaller classrooms, break out sessions at the college/university level.