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Site Update

2002-11-20Are monitor refresh rates at work harming your health?


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Do you, for instance, come away from sessions working with a computer feeling tired, headachey or sore-eyed? Do you suffer from migraines more (or only) after using computers? Even if you cannot obviously see your workstation VDU flashing away like a strobe light, there's a good chance it is improperly configured and a few minutes attention by an IT technician could banish or significantly reduce these ill-effects.

What's refresh? What does this have to do with headaches?

CRT monitors (the CR stands for "cathode ray") operate like a TV; the picture on-screen is updated many times a second in order to achieve the illusion of a stable image. Since the image is not constant but projected by three light guns (red, green & blue), the greater the delay is between 'shots', the more the pupils and retinas of our eyes react to this visual assault. Tiring optical muscles also contribute to headaches and migraines.

Therefore, in the UK, we have legislation to ensure that VDU equipment is capable of sustaining an image which will not unduly wear upon our eyesight. This is the 1992 Health & Safety At Work Act, the relevant portion of which is quoted below:

"Display screen: The characters on the screen shall be well-defined and clearly formed, of adequate size and with adequate spacing between the characters and lines. The image on the screen should be stable, with no flickering or other forms of instability. The brightness and the contrast between the characters and the background shall be easily adjustable by the operator or user, and also be easily adjustable to ambient conditions."

That seems clear, but what are the technical requirements?

It is typically the case that, whilst hardware more than meets the specifications concerned, insufficient attention has been paid to configuring monitor and display adaptor settings within the operating system. This is sad as it is totally unnecessary.

Some dispute may arise because of the lack of a clear legal criterion for a stable image. However, given that ANY video card and monitor combination arising from the past five years will be capable of handling its typical screen resolution (800x600 for a 15" or 1024x768 for a 17") at 75Hz at the very least, this is the most practical working minimum. This is supported both by technical sources:

"The solution is to use a high enough refresh rate. For commonly used phosphors, around 70 frames per second (70 Hz) should be adequate."

...and by retail advisements provided to business and home buyers:

"A 17-inch CRT monitor with a listed maximum resolution of 1600 by 1200 may seem high-end, but if it can display that resolution only at an unacceptably low refresh rate of 60 Hz, you shouldn't be impressed. A monitor's refresh rate indicates the number of times per second the screen gets redrawn. At any refresh rate lower than 70 Hz, your eye will likely detect the screen flickering.",guid,9,page,2,00.asp

For many people, the problem seems to be particularly exacerbated at refresh rates between 50Hz (TV) and 75Hz (average monitor), making 60Hz the 'danger-zone'. What does not help is that operating system defaults are invariably 60Hz, to accomodate both ageing CRT hardware and TFT screens which handle image updating in a different manner. Incidentally, refresh rate increments tend to run 52Hz, 60Hz, 72 or 75Hz, 85Hz, 100Hz, 120Hz... it's quite rare that you're able to specify an exact value.

How can I check my refresh rate configuration or change it?

Firstly, note that there are specific problems with old versions of Microsoft operating systems. Windows 3.x and the original release of Windows 95 did not offer the facility to change refresh rate, defaulting to 60Hz. These operating systems may require hardware-specific drivers to circumvent the limitation, or it may in fact not be possible. However, it is definitely worth trying MultiRes (a free software described below.)

You may be able to alter your refresh rate settings by navigating to My Computer > Control Panel > Display > Settings > Advanced > Adapter. However, your administrator may have disabled this control panel applet, particularly if you are running under NT/2000/XP. There are still some things you can try: not least of which is following the instructions below to discover your refresh rate, prove it to them, and request a fix.

Some monitors offer an on-screen display which shows the refresh rate. Alternatively you can use a small piece of free software by the same name to work it out. Simply download MultiRes and run it, making a note of the frequency rate which appears in the right-click menu. If you use the built-in OS controls, 'Default' is 60Hz and is a bad sign, unless you happen to be lucky enough to work with a TFT flat-panel display unit... also, bear in mind that 'Optimal' may still be only 60Hz if you have a 15" monitor running in 1024x768.

Tip: setting a monitor type (eg, "Super VGA 800x600 @ 75Hz") may get the built-in control panel Display applet to produce usable results. Otherwise, try MultiRes.

Tip: Run 15" monitors in 800x600, and 17" ones in 1024x768 — at higher resolutions, they may be limited to being driven at 60Hz. Again, MultiRes may prove useful.

MultiRes is a replacement Display control panel applet which offers a menu letting you set refresh rate directly, offering you all of the options provided by the driver for your display adapter. If you use it, remember that 75Hz should be safe on any monitor bought within the last few years, but higher rates could (theoretically) damage a monitor incapable of running at them. If in doubt, don't push higher than 75Hz without asking a technician.

Download notes: the latest version of MultiRes — with a full installer — is available from their authors at:, as is a utility called 'OSD' which may be useful on some systems for determining the current refresh rate. MultiRes is provided here as a bare executable so that users who do not have install privileges on workstations may be able to download and use it, if unregistered.exe use has not been disabled. It has been tested on NT/2K/XP and does not require installation; simply download and run.

My IT tech fobbed me off, and MultiRes won't work. What now?

Remember that if you're classified as a user your employer has a legal requirement to assess your workstation. You aren't being stroppy and you aren't hassling them needlessly — "the hardware isn't capable" is not a valid excuse, in addition to probably being a lie. Also, the 1992 legislation is of equal application to schools and universities.

There is very little defence against expert opinion and an act of parliament over a decade old... turning the brightness and contrast down on a monitor may make things slightly more bearable in the immediate term, but does not eliminate the problem of eyestrain. Ultimately, your health should dictate how far you are prepared to take complaints in the face of adversity. You have much on your side, not least of which is the virtual certainty that any hardware you use is capable of meeting the demands of the law... and your well-being is worth more than the ego of a grouchy IT tech.


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