Posted By Sean Fraser I'm not an expert on this Tony but my understanding is that the refresh rates contribute to flicker and can be percieved consciously and sub-consciously, exacerbating general eye and body fatigue. Higher refresh rates do not have this debilitating effect. L26, the HSE guide, may have more on this but the free booklet "Working with VDUs" doesn't mention it, so I would think this is no longer a problem for modern machines - might still be a problem for older installed screens though.

Posted By John Webster Sean is on the right lines. In effect, what you see on the screen is renewed many times per second (Hz). It is possible to consciously or subliminally detect a slight flicker of the screen which can lead to headaches or a feeling of tension, nausea etc., in a similar way that some people are affected by working under fluorescent lights. The lighting can also exacerbate screen flicker. The higher the refresh rate, the less likely it is to have this effect. I recommend a refresh rate >60Hz. The drawback is that the colour definition may be reduced - for example my screen is currently working at a refresh rate of 85Hz but with 16bit High Colour. If I wanted to display 32bit True Colour, I would have to accept a lower refresh rate. The settings can be checked and adjusted on Windows computers (probably most of us) in "Start", "Settings", "Control Panel", "Display" and then selecting the "settings" tab. Depending on version, the refresh rate may be displayed, or you may have to click the "advanced settings" key to find it. Unfortunately, this seems to be an area that often gets overlooked in DSE assessments. Note that if your monitor has a seperate power supply or switch, always ensure that the monitor is on before the computer is booted up or it can revert to some default monitor settings. Hope some of you find this of use. John

Posted By Sean Fraser Good point about the DSE assessment questionnaire - I am away to check ours right now!! We are fortunate in having an IT department so I just checked my monitor settings and am sitting on the fastest refresh rate already.

Posted By Tony Clark Thanx for the help. Do you know if there is a level that must be achieved. Are these just recommendations or is there a legal minimum refresh rate etc. regards Tony

Posted By Laurie I think most televisions, once again the big bulky ones, not the new, expensive, thin ones, have a refresh rate of 50 Hz, tho' of course you don't sit as close as with a VDU. Some manufacturers make "100 Hz" TVs, and it is the refresh rate that they are referring to, but Alec may know different! Laurie

Posted By John Webster Alec I'm sure you are normally right, but this computer had a monitor transplant last year. Now if I boot up without having first switched on the monitor, it reverts to some other settings. It took me quite a while to work out why on some days the flicker was annoying me and on others not. So if it can happen to me, it can probably happen to others. I have experienced other peripherals not performing correctly if not already powered up before "Windows" loads. I certainly wasn't advocating separate power switches!

Posted By Alec Wood Jon, the problem you are having would indicate that the incorrect driver is being used in windows, or that the units DDC data has become corrupted, or the driver is just poorly written and does not support your monitor unit correctly as many are. When you switch the monitor on it flags the PC to read the DDC information. Hence, in your case, the unit has been made to operate outside the paramters specified by the (possibly corrupt) DDC data, or possibly poor driver, and as long as you do not switch it off, or ensure you do switch it on before the PC, then the DDC data will not get read and Windows will not implement the setting specified by the DDC data. I bet that's as clear as mud! John, in theory it is possible. In practise, modern CRT monitors (post 1998) have almost always used a micr-controller at their heart with a phase locked loop to control the sync signals used to drive the horizontal and vertical scans. If you set a mode unsupported by the unit, rather than damagiung itself by exceeding its capabilities, it will just go into low power mode (DPMS) and the power light will suaull flash amber/green at you. If you are using Windows, and the correct driver, the display properties will only offer you rates supported by the unit, if the driver has been written correctly (see above). TFT units work differently, you will not damage one by sending it data at too high a rate, but then, since they do not refresh in the same manner as CRT units, there is nothing to be gained from using a higher refresh rate in such units anyway. Flicker on those is from flourescent lamps inside, but they run at 2500-4000Hz so should not give rise to any problems. Alec Wood Samsung Electronics - An ex monitor manufacturing engineer in case no-one had guessed :-)