We frequently get asked what size of screen is required for a particular application. It could be for a projection screen but this can also apply to plasma, LCD and LED screens where a group of people are going to view information.
The first thing to consider is what type of information is being displayed. This usually falls into one of three categories.
This category covers the bulk of information displayed at conferences, seminars, lectures and meetings. It is typically PowerPoint or Keynote type of graphics and hopefully, if the presenter has employed best practice the size of the text will be large, the images bold and not lots of detail. Watching films and playing videos will usually fall into this category too.
Sometimes it is necessary to look at spreadsheets and Word docs on large screens. This isn’t the same as in a presentation where the information on the screen is used to support what the presenter is saying but where the audience is required to actually read all the text or data. Font sizes are usually much small and 10-12pt text is typically used in Word Documents and Excel workbooks.
This category is where detailed information needs to be displayed. Resolution becomes hugely important as well as screen size. Think of engineers reviewing design drawing or medical consultants looking at x-rays and scan results and you will get the idea.
As the bulk of usage falls into the General Viewing category let’s consider this first. There is a useful calculation to determine the optimum size of screen and that is that the distance to the furthest person in the audience should be no more than eight times the height of the screen.
The table below shows the maximum viewing distance for common projection and LCD/plasma screens. If you know the size of the room or how far away the audience will be you can look up the appropriate screen size.
|Max Viewing Distance||Screen Type||Screen||Screen Size|
|m||ft||Format||metres (w x h)|
|4.2||14||42” Plasma/LCD||16:9||0.93 x 0.52|
|4.6||15||46” Plasma/LCD||16:9||1.02 x 0.57|
|5.5||18||55” Plasma/LCD||16:9||1.22 x 0.69|
|6.0||20||60” Plasma/LCD||16:9||1.33 x 0.75|
|9.1||30||5’ x 3’9” projector screen||4:3||1.52 x 1.14|
|11.0||36||6’ x 4’ projector screen||4:3||1.83 x 1.37|
|12.8||42||7 x 5’2” projector screen||4:3||2.13 x 1.6|
|14.4||47||10’2″ x 5’11” projector screen||16:9||3.1 x 1.8|
|14.6||48||8’ x 6’ projector screen||4:3||2.44 x 1.83|
|16.5||54||12’7″ x 6’9″ projector screen||16:9||3.66 x 2.06|
|18.3||60||10×7’6” projector screen||4:3||3.05 x 2.29|
|21.6||71||15′ x 8’10″projector screen||16:9||4.6 x 2.7|
|22.0||72||12×9 projector screen||4:3||3.66 x 2.75|
But what about Reading and Inspecting?
The above table shows maximum viewing distances for General Viewing only. If your use falls into the reading category you should divide the distances by 1.5. Similarly, if you need to display detailed information the distances should be divided by 2 to get the results for Inspecting type of viewing.
The issue of ceiling height
It’s all very well being able to understand the ideal size of screen for your particular application but there are plenty of situations where it isn’t practical to use that ideal screen size. The most common problem is ceiling height, or more specifically, the lack of it.
You need to consider that when seated the average head height is 4ft from the floor and eye-line would be approximately 3ft6”. It is necessary to ensure that the bottom of the screen is high enough so that the heads of the audience don’t obstruct it. Realistically this means that the lowest part of the projected image wants to be at least 4ft above floor level. If it is really necessary you can get away with a little less but certainly not below 3ft. For larger audiences and greater viewing distances, it would be preferable to lift it to 5-6ft from the floor.
What this means is that you can quickly run out of headroom. Typically, to use a 10ft 4:3 format screen would require floor to ceiling height of between 3.5m and 4m. It is common to find large multi-function rooms used for conferences that are capable of accommodating several hundred people with ceiling heights less than this.
In situations where there isn’t adequate headroom to accommodate the optimum screen sizes, you can consider using multiple screens to reduce the maximum viewing distance. ‘Repeater screens’ positioned away from the main presentation stage are often used for this purpose. Alternatively, when you are aware of the issue, the simplest thing to do is to ensure that the information put on the screen is sufficiently large so that viewers at the extremities of the room can still read it. It might just be a case of bumping up the font size or splitting tables so that not so much information is presented on the screen.
I hope that helps with determining screen size. It’s a common question and an important consideration however when selecting a projector and screen for a particular application resolution, brightness, colour and contrast ratio should also be considered.
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