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The Truth About Flourescent Lights?
plato is desperate for answers to the following questions: "Help! I, for one, am driven insane (eg., headaches) by the flickering and buzzing of flourescent lights; I know others are plagued by the same problem and am looking for some answers. At what refresh rate do flourescent lights flicker? Why does flickering (eg., flourescent lights, computer monitors with bad refresh rates, strobe lights) cause headaches for some people? What are some better alternatives to flourescent lights for an office environment? How cost effective are they (in the short- and long-term) compared to natural light, (which isn't always an option)."
While not strictly relevant, I've read in the past of efforts to collect sunlight at the tops of buildings, pipe this light down to individual rooms using fiber-optics, and re-distribute it with holographic panels. In theory, the result would be pure sunlight radiated in a very natural pattern, much like a natural skylight.
Has anybody heard of any applications of this idea?
I worked in a cube farm in a room that had been converted from a training/meeting room. The primary lighting was fluorescent. When the fluorescent lighting was the only light source, people startd developing headaches.
Interestingly enough, the people who were screaming in pain were those with 56 or 60 hz refresh rates on the monitors. Replacing the monitors with newer models capable of 72 hz or higher refresh rates eased the problem to tolerable levels.
We solved the problem by using the secondary light system as much as possible (low wattage incandescent floodlights). Management didn't like the "mood lighting" though and would turn on the fuorescents whenever they wandered by.
Eventually we used the ADA (only applies if you are in the US, but I'm sure many countries have similar legislation) to force the fluorescents off (one member of the group had chronic migraines triggered by harsh lighting, especially flickering). It's amazing what you can get declared "reasonable measures" to meet the needs of a "disabled" worker! The ADA is your friend!
"Flame away, I wear asbestos underwear"
Real geeks code in the dark :)
-ElJefe
Because the lighting is so important for my reeftanks and freshwater plant tanks, I've learned a lot about different types of lighting. One thing that these tanks absolutely need is full-spectrum lighting. In contrast to the el cheapo cool-white fluorescent lamps which emphasize one or a few parts of the light spectrum, full-spectrum lighting provides light over the full color spectrum. This results in a more natural, less harsh light. The full-spectrum light that's widely available in a variety of sizes is the GE Chroma50. I spec it for every new office I move into. I don't know if this will help with the flickering problem, but at least the light quality will be better.
I've studied this a lot, without the help of my employeers, I might add.Turns out there are three problems. The flicker rate of the florescent (magnetic ballast, 60 Hz in USA), the refresh rate of your monitor, and glare.
You may be able to replace the existing florescents with compact florescents (electronic ballast). They often use a higher flicker rate, and they use long persistance phosphers that glow longer and reduce flicker (remember the original IBM PC's green monitor - had long persistence phosphers also). Yes, you can get electronic ballasts for standard fixtures that take 48 inch tubes.
Indirect lighting is almost always better for computer users. I usually use a halogen up-light (six foot tall "torch" that points at the ceiling). Reduces glare, and reduces flicker (any light source based on a hot filament has minimal flicker since the filament tends to stay at a pretty constant temperature).
The best, of course, is north facing windows. Excellent light quality (perfect color temperature, zero flicker), and no glare. Damn few archictects know or care about this (Frank Lloyd Wright taught us this in the 1910s or so), sadly. Shame on the jerks that design "modern" office buildings!
Obviously, you should have the best monitor you can get, running at the highest refresh rate your video card can use with the resolution you need. I'm running 1280x1024x24 @85Hz on a 21 inch monitor.
A forth overlooked problem is that of seating position, but that's not the subject here...
I am posting from the UK so some of my terminology may need "translating" for the US Market.
Ordinary, Low Frequency (LF) Fluorescent likes do have noticable flicker which can certainly upset some (many?) people.
There are many ways of reducing the problem
1) In large installations the lighting should be wired such that each area is lit by lights on all three phases. This reduces the perceived flicker.
2) Where three phase power is not available you can buy "lead/lag" fittings with two tubes wired such that the flicker in each tube is out of phase. These are only available in small sizes and are hard to get.
3) The unpleasant effects do seem to be reduced if the you can bounce the light(s) off another surface
4) But the best solution is to use "High Frequency" Ballasts and tubes. This converts the incoming supply to DC and then uses a high frequency inverter to run the tubes. They offer lower weight and better efficiency than LF Fluorescents. The persistence of the phosphors in the tubes means that there is virtually no flicker present at any frequency.
HF fluorescents have a higher capital cost than LF fittings - but the difference has become much smaller recently. Twin tube fittings are usually cheaper per tube than single tube fittings. You can also get HF control gear which can be dimmed (commonly by a 1-10V DC control voltage).
The phosphors used also have an effect. Older tubes tend to obtain white by mixing of purple with a green/yellow. This gives appaling colouring rendering. There's a measure of this quality called "Ra" which you should be able to check for different types of tubes. An Ra of 40%-50% is typical for older type tubes. Modern tubes are available which use phosphors very similar to those used in colour TV tubes. These have an Ra of about 80%. The offer higher efficiency too. Many people the better "Quality" of light they give reduces the problems they have. These modern phosphors ( often known as "Trisphosphors" ) have a slightly longer persistence - although the difference in flicker levels is small.
You can get tubes with an Ra of almost 100% - but they are rare, expensive and innefficient.
Colout temperature is also important. For domestic environments it is worth getting tubes with a colour temperature of 2700K which is similar to that of incandescent bulbs. This allows different types of light source to "blend" better. Offices tend to use a colour temperature of 3500K or even 4000k - which produces a very tiring "blue" light.
If you are using HF lights then you can get tubes which offer slightly more efficiency. Such tubes must NOT be used in LF lights. If they strike at all the resulting light would be very flickery. It's usually OK to use LF tubes in HF fittings.
When tubes get old the light output starts dropping very fast. This is the time to replace them. as the light output drops the flicker will also being increasing. Most tubes are worn out long before they fail to strike reliably. New tubes frequently swirl for the first few hours of use.
Modern HF fluorescent lights are very much more efficient than other forms of lighting in theory. But in practice though Tungsten Halogen can rival them in many applications because because Halogen lights give a small, point source of light which is easy to control usin reflectors and lenses.
Fluorescents - especially HF types are not a very good choice for things like hallways and stairs which only require to be lit intermittently. This is because they take several minutes to warm up. They light almost instantly - but will only deliver about 5% of their light output, gradually rising to the full level.
AJB