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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)."
There was a show on TV awhile back that said that the eye can detect up to several thousand hertz (this can be seen by monitoring the optic nerve), although there is no "flicker" apparent above 30 hertz or so, and that faster is always better. I recall it took 500 or 600 Hz to control the objectionable eye strains and something like 4000 Hz to eleminate them altogether.
The yellowish mercury free (iron-iodine) lights they are putting in everywhere have an extreme effect on me personally--I really wanted to scream when they took out the old bulbs and put in the new ones (I've been through this at two universities--they could save enough in two years to pay for hiring the electricians to do the switch, plus no hazardous waste mercury bulbs to dispose of from time to time). Others apparently find them less outrageously painful.
I have evolved two solutions:
1. A flourescent desklamp with a natural spectrum bulb. Bulbs from WallMart, about $5. There used to be "office rated" lights with no 60 cycle transformer hum, but now everything is from Taiwan and hums after it gets warm. About $65 versus $95+ for the Swedish ones that don't hum, if you can evern find them (I haven't seen one in years.) The desklamp plus a little natural light will work wonders.
2. A substantial desklamp using either an incandescant bulb (100W) or (best) a really good halogen lamp (50W,about $50, although sometimes on "clearance" for $30 or so). Get the one with the counterbalance, length adjustments on the arms, and 2 intensity levels if you can.
The economics are such that you will never see the really good flourescent illumination again. The mercury free Trimline (tm) bulbs with their reduced power coonsumption will be the choice of building managers for the indefinite future. You have different things going on inside the bulb, and different phosphors, and much lower intensity (the human eye is more sensitive to yellow light, so less light intensity appears bright nonetheless). The old office had 4 or 5 times the illumination level, and the higher powered bulbs seemed to give a more constant illumination--maybe they didn't cool off completely in the ionized core, or somehting. Anyway, those days are gone forever.
That flickering you're seeing is not the flickering of the light or the display; it's the interaction of the two. The human eye can detect flickering at a maximuim of somewhere between 12 and 24 Hz (can't remember which one, I think it's 12) due to persistence of vision (this is how animation/movies work; film updates at around 24fps from memory). If the refresh rate of the display is close enough to the flicker rate of the lights, you will then get flicker due to the beat frequency which is abs(f1 - f2). I believe harmonics can come into this as well (they do, but it's the exetent to which they affect things that I reffering to). Solution: either adjust your refresh rate or turn off the lights. BTW, this is explained in the display timings faq in XFree86 (written by ESR). Sorry, no link.
Bill - aka taniwha
--
Leave others their otherness. -- Aratak
They don't use anything cool like fiber optics, though. ;)
Curiously, though, do you have any idea how much these Solatubes cost? I can't find anything resembling a price on their web site...
"Holographic" was the word used in the article I read. I don't remember the specifics (that's kinda why I was asking), but the light was either piped against or through the back of some holographic film, presumably to get an even, full and rich distribution of the light. I wish I could find a link to that...
At work, one of the office workers had to go home because of epileptic seizures possibly induced by the flourescent lights. I changed out both the ballasts and the bulbs and have not heard of any problems since.
There might be other ways to reduce the annoyance of 60Hz flicker, such as angling the desk and reflective framed pictures on the wall, or even placing large plants around the desk. Arrangement of the office can have wonderful effects besides increasing window light. It can really liven up a person at work.
I took part in a series of psych studies where they were measuring the rate at which your brain processes information and relating this to IQ. The good news is that they found a direct correlation. There were a lot of different tests, but one that's relevant used a flickering light controlled by computer and you had to say if it was constant or flickering. Over a series of tests they determined the fastest speed at which your brain perceived the light to be flickering.
:-)
There's no thinking involved as such in this kind of test: either you see the light flickering or you don't. The bad news is that people of the highest IQ (measured by 6 different kinds of test - it took days!!) could detect flickering down to 16 milliseconds (IQ of 130-140) which is about 62Hz. Lowest IQs tested (90-100) were down around 30ms. The relationship was *roughly* linear.
Hence, next time you're in a room and you're the only one complaining about flickering lights or screens, you might just have to console yourself with the thought that you're the brightest person in the room!
Personally, I had the fastest flicker rate (16ms), I notice flickering lights and screens if I think about it, but don't seem to be adversely affected by fluro lights. Maybe I'm just used to it (my original PC ran at 1024x768 *interlaced* ugg!! I used to think it was horrible to stare at, but strangely, after a few weeks I didn't notice any flicker at all). I'm sure other factors are also involved. (similar to the story of the guy with the upside down glasses, but that's a major digression
By the way, I much, much prefer the new "daylight" fluro tubes you can get, which have a much more natural spectral distribution, making other fluros look yellow or brown by comparison.
pithy comment
There are phosphors which glow longer, there are ones which produce a different spectrum (combination of colors).
Or, if it's your house, change the light fixture. Start by replacing the "starter" in case a bad one is interfering with the bulb's power. There are also different power circuits available for various bulbs. Or you can change from fluorescent to the various low-energy vapor bulbs. Or put in a track light or X-10 controllers so you can adjust the lighting in different ways to suit the situation...such as giving some chairs spotlights for reading, or turning lights off when watching a movie.
You can run flourescent lamps off DC current. The problem is, you generally need to convert it into AC to be able to efficiently raise the voltage.
Plus, an inductor is good for regulating the current flow to the bulb.
Compact and other flourescent tubes that run on DC usually use a high frequency oscillator and a small transformer to get the high voltage. With high frequency, you can use a much smaller (physically) transformer and retain the same efficiency. }:)
- =^o.o^=
I prefer incandescent, of course. I make sure that the shade performs its function well (doesn't shine direct light into your eyes). I place it somewhere behind the front of the monitor (right now, to the left, on top of my subwoofer).
In an office environment, you may have trouble getting this unless a doctor recommends it.
Ideally, you have your own office (I hate cubicles, but that's a given) that you can simply turn off the flourescent light in.
Oh yeah, flourescents give off *lots* of noise. You can demonstrate that with a microphone. That may be another "playing card" you can use with your employer.
There are a lot of popular misconceptions about fluorescent lighting, and I see a lot expressed here.
Good quality modern fluorescent lights that are operating properly don't have a perceivable flicker. Easy to prove: Hold a stick (pen, pencil ruler) up in front of you while looking at the light. Hold it by the end and shake it back and forth rapidly in an arc. You should see a smooth blur. Do the same thing in front of your monitor. You'll see a strobe effect, several apparently stationary images of the stick or whatever.
(Do this in front of a TV (in the US, NTSC type) and you'll see a curved image of the stick.)
The reason they don't flicker is the same reason you can still see the image at the top of a monitor when the electron beam is scanning the bottom of it - persistence. The phosphor that gives off the light continues to glow after the electrons stop hitting it.
Different phosphors have different persistence, which is a good thing. If you had a long-persistence phosphor on your TV screen you would get trailing images when objects moved rapidly.
Phosphors used in lighting today have fairly long persistence. You may be able to detect the variation using something like a strobe wheel (spinner with lines spaced at regular intervals, often used or found on record turntables), but you shouldn't be able to see it in normal circumstances.
The "flicker" rate is 2x the rate of your AC current - 60hz in the US, 50hz in some other countries. Because the current has a peak voltage in each "direction" once per cycle, you get two peaks and two "troughs" in one cycle, so the correct rate for the US would be 120hz.
Aircraft and some military installations, along with some unusual building installations, use 400hz AC power, which would yield 800 "flickers" per second.
Different phosphors also give off different colors. Depending on what you want to light, you can choose the color. Grocery meat counters are often cited as a place where a warmer, redder light makes the product look better. Graphic design studios would want a more even color for accurate perception of what they are working with.
The pinkish high-pressure sodium vapor lamps actually have a pretty neutral color, unlike the older mercury vapor designs, which are blue to green. Many people didn't like the new style at first because it seemed so pink next to the mercury.
LOW-pressure sodium lamps are monochromatic yellow. They were cheap, they didn't attract as many bugs at night, but you often could not tell the color of a car under them.
If you're getting headaches at work, it's not because you're under fluorescent light. It's most likely that the lighting isn't appropriate to the work you're doing (or there's some other factor like your monitor).
It COULD be because you're under BAD florescent light. Fixtures need to be cleaned, bulbs need to be replaced, and so do ballasts on a regular basis. A fluorescent lamp can loose fifty percent of it's light output before it finally quits. More than sixty percent of the possible output is often lost to dirt on the lamp and fixture.
Cheap fluorescent lamps might not have good phosphors in them, giving bad color and possible 120hz flicker.
Bad ballasts CAN induce a noticeable flicker. They're noisy, and noise causes fatigue, and they're dangerous - they can catch fire and even explode.
One reason STROBE lights or lights without phosphor can cause people problems is that there are natural brain wave patterns that will try to synchronize with the frequency of the strobe. One of these is slightly below 60hz, and early research on Attention Deficit Disorder (ADD) thought that fluorescent lights were speeding this up and causing the hyperactivity of the kids. (For the reasons above, this theory was discarded.)
So if you're getting headaches at work, don't bitch about it being from fluorescent lamps. If the lamps flicker, try to get them serviced. If the ballast gets noisy, it's going to go out soon and needs to be replaced. Report it. Look at other factors such as glare, too much or too little light, bad positioning of your monitor, poor monitor quality, and for those of us over 40, failing near vision. A good rule for the lighting level around your monitor is that objects you see around it should have about the same light level. A black screen with white or other bright colored text against a well-lit bright background will cause problems, as will a white screen with some dark text against a dark or window.
An article in today's Guardian talks about a new LED they've made from Gallium Nitride. It uses eighty percent less power than a conventional light bulb, plus it will last for 100,000 hours compared to 1,000 for normal. This is a quote from the column:
.sig here.
"In principle all these fluorescent tubes, so long and ugly, you could replace with these tiny light emitting diodes in any shape you want. The actual LED is a fraction of a millimetre across."
The output of these devices is equal to that of a conventional tungsten filament bulb.
No matter what it looks like, there isn't a
No matter what it looks like, there isn't a
I've measured it, and it goes so close to dark the difference isn't worth talking about. The phosphors are clearly very short lived (less than a millisecond). The trace from a photodiode looks like abs(sin(x)).
FULL SPECTRUM is the way to go. There are full spectrum incandescent bulbs (have to look for them) and full spectrum fluorescents as cheap as $7 per bulb at Home Depot and I think I saw them at Wall Mart too. I use both.
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