I have an issue with some employees finding the lighting in the offices very harsh, and giving them head aches. The lights are the type that has a curved mirrored background with mirrored dividers making a grid pattern with no diffuser covers. They are sold as energy saving as they do not light the ceiling. This however coupled with some of the new replacement fluorescent tubes are causing some problems. You seem to be able to get different colour ranges of tubes, do any of you have any experience of this issue and what you selected to make the environment less harsh/ clinical. This is just a normal office with people sat at desks with computers and the odd bit of paper. No engineering drawing or graphic design etc. We have tried removing some of the tubes, but that is not really working. There appear to be :- Soft white tubes, cool white, warm white and natural light options. Has anyone been down this path, and would you be willing to share your findings. The lux level has not been measured, but from previous dealings it is probably around the 500 lux mark ( but this is just based on previous use of light meters on desks in the past). I know office lighting should be around 300 to 500, so that would put us on the top of that range. It does not seem to be the level that is the issue more the harshness. Thanks Chris

We find that there is also a variance in problems in relation to age. It seems the younger generation are the one's who are having these difficulties whereas some who are older need the brighter harsher lighting. We too have taken out of action certain tubes to reduce Lux levels to a more average than top end level. I have heard that you can get opaque filters for them too, but have not seen them in use so cannot comment.

Go for around the 3000K (cool K= Kelvin) the higher temp (4500 - 8000K) give a cool white light. The lower temps give a warmer less harsh light.

Don't remove the tubes & leave the fitting energised unless the whole section relating to the tube has been correctly isolated / disconnected inside the fitting, as this poses a fire risk, the remains can overheat and thus catch fire with no tube fitted. Yes I KNOW it does not make sense, but it happens!

Good suggestion by Zimmy at #8 about high frequency. Back in the 1980s I understand that the Medical Research Council (MRC) found that modifying fluorescent light fittings to operate with a frequency much higher than the usual one of 50 cycles per second (cps) could be beneficial. The MRC carried out covert experiments in one or more office premises where a significant proportion of employees had complained about glare, headaches and/or other problems ascribed to light from such fittings. Employees completed questionnaires at intervals about what effects they experienced, when and for how long, etc. After a while, and unknown to the employees, the fittings were modified (apparently a fairly simple and inexpensive task) so that they operated at (?) 30,000 cps instead of 50 cps at which 240 volt mains electricity is usually supplied in the UK. After the modifications were made the MRC found from questionnaires that the incidence of problems diminished significantly. The MRC report suggested that though a fluorescent tube operating at 50 cps appears to provide a visibly continuous light, the brains of some people can subconsciously detect the light flickering at 50 cps and be vulnerable to headaches caused by such flickering. Therefore, a significant increase in the frequency will effectively eliminate the subconscious/subliminal flicker effect. (I vaguely recall writing about this aspect of fluorescent lights on this forum some years ago, but can't locate what I wrote, so perhaps my memory is playing tricks or the forum search facility isn't very effective.) Another related point: The frequency at which fluorescent lights operate is also a crucial matter in workplaces containing machines which have rotating parts capable of moving at speeds which can match the lighting frequency, even if only for short periods. Years ago, probably during my training with HSE, I saw a training video featuring a woodworking circular saw machine with a blade which appeared to be stationary. However, when a piece of timber was presented to the blade, the timber was promptly cut in half and generated a cloud of dust and chippings. Viewers were told that the blade appeared to be stationary because its rotation speed matched that of the fluorescent lighting. One suggested method of overcoming the problem was to illuminate such parts of machinery with lamps incorporating conventional incandescent filament bulbs.

The blade appearing to be stationary due to the strobe effect. The blade has exactly the same rotational frequency as the mains supply at which the fluoro is flashing. UK 50Hz. That is 3000 rpm. This is easily avoided with flouro's being distributed across 3 phases around rotationg machines moving the strobe frequency up to 150Hz, you could get hish speed spindles funning at that, but, not many things run @ 9k rpm that you have easy access to such as a table saw, thinking wood working, a spindle moulder is however one. There are other things that can be done, both of which are mentioned here, HF fluoro's, local incandescent task lighting. Also, the mains frequency in the UK is goverened by statute law to be +/-1% of the nominal for 99.5% of the year, this gives a rotational speed of 2970 to 3030 rpm, with the final 0.5% of the year it is allowed to vary +4 / -6%, giving a speed of from 2820 to 3120 rpm. Now it is the lower end of the frequency band we are concerned with for conventional machinery powered via conventional motors without any sort of electronic speed control (of which there are loads that we won't go into the detail of here). A motor running at 50Hz has a synchronous speed of 3000 rpm, hence where the possibility of the strobe effect comes in. However, @ 3000 rpm, the motor cannot generate any torque, because there is no slip. For an induction motor to generate torque, slip must be present. See the pdf here for one motor manufacturer I use, you will see that the nearest to 3k is 2950, just outside the 99.5% zone. http://www.tecmotors.co....es/TECA%20IE1%20Elec.pdf If you have speed control then the motor speed can be made to match the strobe of the lighting, whether this be accidentally or by design. It is a rare occurance to view a perfect strobe effect without it being artificially created. Good electrical circuit design will see the lighting load shed across 3 phases, this will reduce the risk, HF lighting is popular, other sources of light, natural, incandescant, LED will all reduce the scenario. HOWEVER, you do need to be careful with LED as these, can, also strobe. Switch mode power supplies can, also generate strobing, and, can be used to control LED lighting. Currently with LED, there is a lot of cases where you get what you pay for. Fitted machine lighting even though it may be fluoro, is likely to be transformer fed, this will likely give it a phase shift in relation to the surrounding mains fed fluoro's which will reduce the strobe effect. HTH.

I hope they don't have any circular saws in the office :0) Thanks all for the information as Zimmy in #8 noted I actually think it is more glare than lux level. I may buy a cheapo light meter as it does not need calibration on the basis there is no hard and fast rule for a normal desk 300 to 500 lux, so even if the thing is 10% out, 400 could read 360 or 440, so it will give an idea. One of the people involved has sat at the same desk in the same position for 2 years, with the only thing changing is the tube. Hence I figure if I go back to a softer/ warmer light all will return to a state of equilibrium. I would have thought that if frequency was an issue it would have been an issue with all tubes, wouldn't it. However something else to think about if plan "A" fails to get results. Thanks all for the info, very helpful. Chris

A few years back we had an office refurbishment that replaced / upgraded the lighting. One member of staff immediately complained about headaches when sat at one particular desk. We went through the humidity, lux, eyetests routine to no avail. Deeper and "off the wall" investigations looked at screen refresh rates (this was a CRT screen) and by luck picked up the refresh rates of the lighting which revealed the new h/f light above the desk was flickering at 50hz compared to all the others at 100hz. Out of hours the fitting was quietly changed and nothing said about it. A couple of weeks later when asked how were the headaches all had been resolved. We had used a CRT tester purchased from Black Box for schecking refresh rates of monitor screens. They aren't available now but I have one that still sees service from time to time on just this aspect.