fluorescent lighting

Fluorescent Lighting

    and Other Optical Issues

Flicker, Drowsiness, Migraines, Optical Sensitivity

This ranges from excess light to monitor flicker

Fluorescent lighting commonly causes problems, generally associated with a perception of flicker. These include drowsiness, headaches, migraines, and difficulty in concentration.

It's Not Actually Flicker ...
          ... It's a Physiological (Neurological/Optical) Effect of Fluorescent Lighting.

It is very likely that what is perceived as optical flicker is not optical flicker at all. Rather, it is the effect of fluorescent light on the person's own optical response.

Little is known about the actual cause. The most probable explanation is pupillary flutter caused by the spiked spectral pattern emitted by fluorescent lights.

In explanation, fluorescent lights rely on ultraviolet light being fluoresced down to visible light frequencies (hence "fluorescent"). The spectral light output is not continuous; rather it is a series of spikes. The spikes cause the pupil to alternately dilate and contract in response to red and blue spectral peaks in the light. The result is that the pupil erratically adjusts or "flutters", known as "red-blue pupillary flicker" or "red-blue pupillary flutter". Red-blue pupillary flicker is believed to be the cause of:
  1. perceived flicker
  2. neurological effects such as headaches, migraines, drowsiness, general fatigue and malaise.


What is perceived as "flicker" is probably related to:
1.   Flicker caused by the effects of the light spectral pattern of fluorescent light bulbs.
This occurs with all common fluorescent lights, including compact fluorescent lamps (CFLs), other types of electronically ballasted lights, and old style magnetically ballasted (line current) fluorescent tubes.

2.   Flicker at line current frequency.
The flicker is at 100 or 120 Hz (half-cycles for 50 or 60 Hz current), which theoretically cannot be perceived. The probable reason magnetically ballasted fluorescent lights are perceived as flickering by more people is that the line frequency flicker (100/120 Hz) creates a sympathetic response. What we see as flicker is an effect of the pulses as sensed by the retina. The actual flicker effect is caused by the effects of the light spectral pattern of fluorescent light bulb on the eye.

3.   Low frequency flicker caused by worn out equipment.
This is another aggravating factor in fluorescent flicker.

4.   Poor light quality in terms of narrow spectrum light output.
All common fluorescent lights have poor quality spectral output, and exhibit a spiked spectral pattern.
The neural or pupillary response issue is poorly understood; however, it is known that fluorescent lights are unsatisfactory for a significant portion of the population. Some people who have problems with fluorescent lights seem to be less affected by compact fluorescent lights (CFLs) and other fluorescent lights which use electronic ballasts.

Unfortunately, CFLs and other electronically ballasted lights do cause problems for some people. Therefore, the "flicker" hypothesis does not explain all of the problems with fluorescent lighting. A significant number of people do not tolerate any fluorescent lighting well.

The Cause of "Red-Blue Pupillary Flicker"

Fluorescent lights function by creating an ultraviolet (U-V) source light generated by energizing the mercury vapour inside the tube. This source light, at 253.7 nm energizes phosphors on the tube, which fluoresce the light down to multiple visible frequencies. The phosphors are balanced so that the total output is perceived as white light of the desired colour temperature. The output from the phosphors is highly dependent on the source light (the mercury vapour inside the tube).

The problem is that the output from the phosphors is not continuous across the visible light spectrum, but rather comprises a series of spikes. This is a function of the combination of the (253.7 nm UV) source light and the phosphors. While the visible light is emitted by the phosphors, the spectral output is controlled by the (253.7 nm) source light, which is the reason for the spiked output. (See graphs below for examples.)

It is this spiked lighting pattern that is believed to stimulate red-blue pupillary flicker.

LED Lighting

LED lighting uses similar phosphors; however, the source light is of a broader spectrum. (This is presumably due to variations in the valence band and Einstein coefficients of the particular LED, but I leave this to photonics experts to describe.) As a result, it is likely that LED lighting will be much less likely to provoke red-blue pupillary flicker.

Commercial, Retail and Restaurant Lighting

The problems with fluorescent lighting are recognized by retail and restaurant businesses, many of whom have moved away from fluorescent lighting. This is not an issue of line current flicker, as the current standard for fluorescent lighting is either CFL or electronic ballasts.

LED lighting, despite its higher cost is finding increased application, especially for low intensity light sources such as spot lighting. (Higher intensity lighting is generally sodium or other HID lighting.)

HID lighting of various types seem to be favoured by greenhouse farmers (apparently marijuana growers) over fluorescents, although it appears that this relates to the desired infra-red light component, which has an effect on stem growth. Large scale LED lighting is also favored, and there are several sets of instructions on the web directed to constructing D-I-Y high output LED arrays, which appear to be directed to this industry. Typical illumination values described for marijuana agriculture are 10,000 to 30,000 lux, so this may be associated with electrical efficiency. It is also possible that growers in some areas are focused on increased efficiency because high energy use by fluorescents (yes, they are high energy consumers!) can disclose their production to authorities.

Blue / Blue-Ultraviolet Sensitivity
    - another issue with fluorescent lighting (because one issue is not enough)

Blue or blue-ultraviolet sensitivity appears to be a separate issue involving sensitivity to fluorescent lighting.

Blue or blue-ultraviolet sensitivity is a response by some people to blue light. A person with this sensitivity will experience the following:

Sensitivity to faux HID headlights.
These are blue-tint halogen bulbs intended to display a bluish tint to mimic HID lighting, which typically operates at a higher colour temperature. To a lesser extent, so-called extra-brightness halogen bulbs exhibit this bluish tint. (As headlight illumination, these bulbs actually reduce night vision.) While many people find faux HID headlights unpleasant, a person with blue sensitivity would find this type of lighting particularly stressful. [1]

Increased sensitivity to fluorescent lighting with blueish or high colour temperature output (e.g., 4100°K "cool white", or 5300°K, 6350°K and 6500°K "daylight"), as compared to fluorescent lighting with a lower colour temperature (2700°K "warm white" or "soft white").
This would include people who are comfortable with warm white CFL lights but find high colour temperature fluorescent lighting significantly more stressful.

Sensitivity to common LED lighting
This may not be present with LED lighting below 3000°, and probably does not occur with remote fluorescing LED lights (e.g., the ones with yellow envelopes).

Sensitivity to black lights
Black lights do not induce red-blue pupillary flicker because black lights do not contain red-producing phosphors.

Sensitivity to colour lighting having a blue component, especially colour LED lights (which are more monochromatic than colour-filtered incandescent lighting).
Blue or blue-ultraviolet sensitivity is believed to be affected by a manifestation of the Opn5 gene sequence in those affected by this phenomenon. It is not clear to what extent blue sensitivity affects people who are sensitive to fluorescent lighting. Blue sensitivity does not appear to initiate migraines, but could nevertheless enhance the tendency of other effects causing migraines.

GE appears to recognise this colour temperature issue. While GE "Reveal" incandescent bulbs have a decidedly blue tint (colour temperature of 3400°), GE "Reveal" CFL bulbs (i.e., the fluorescent version of the "reveal" line) have a colour temperature of 2500°K and (fluorescent) "Reveal" tubes 2600°K, which is lower than a conventional 2700° "soft white" CFL.

Effects of Fluorescents

There are various physiological effects associated with fluorescents including:
This is significant both because of the actual effect (the migraine headache which is associated with most migraine attacks), and because the migraine is a tangible physiological effect.

Related neurological effects
This can include drowsyness, general stress, and adverse effect on mood.

Strobe effect
This affects use of machinery, particularly when using old-style magnetic ballasts, which have an actual flicker or strobe effect at 2x mains frequency (100 or 120 Hz).
Multi-Factorial - It is likely that one type of physiolocial response to fluorescent lights can be compounded by a different effect.

The most apparent combination of effects is the sympathetic response to line current flicker that some people experience with old-style magnetically ballast fluorescent lights. The primary effect is that of pupillary flutter, but the 100 or 120 Hz flicker sets up a sympathetic pattern to the pupillary flicker. As a result, an old-style fluorescent lamp can be perceived as more intensely flickering than an electronically ballasted fluorescent lamp or a CFL.

The most significant aspect of the multiple effects is that sensitivity to fluorescent lights is often multifactorial. For example, a person sensitive to red-blue pupillary flicker may find the effects more pronounced with cool white or "bluish" fluorescent lights.

This also means that it is difficult to access the precise cause of physiological problems caused by fluorescent lighting.

Compact Fluorescent Lights (CFLs)

"Compact Fluorescent" lights are the small fluorescent lights designed to replace an ordinary incandescent bulb. They use an electronic ballast that operates at 20 kHz to 60 kHz.

Compact fluorescent lamps (CFLs) are useful for areas that need continuous lighting, but light where quality is unimportant, e.g., a common hallway. They may not be economical for lights that are switched on for short periods of time.

Compact fluorescent lights (CFLs) do not resolve the problems experienced by many people with fluorescent lights, and there are definitely people who cannot tolerate the lighting of any fluorescent light source, including electronically ballasted fluorescent lights.

Use separate lights for security lighting and the like.
A 15 watt CFL on a timer is a lot cheaper to operate than an ordinary room light. When you're spending time in the room with the regular light on, the fluorescent light on the timer won't be much of an irritant. Also, with the timer, you can manually switch off the fluorescent light, for a single timer cycle, at will.

A CFL in a room which also has incandescent or natural light will have significantly less adverse effect (provided that most of the illumination comes from the incandescent lighting).

Technical information related to CFLs and lighting quality here.

Electronic ballasts are available for standard fluorescent lamps, which is a good alternative if you have fluorescent lamps already installed in a place you own.
These are apparently 20% more efficient than conventional magnetic ballasts. Electronic ballasts are equivalent in cost but are far less costly to use because of longer lamp and ballast life in addition to the reduced power consumption. (i.e., magnetic ballasts are obsolete.)

It may well be that conversion to electronic ballasts is already more economical than leaving the old ballasts in place.

LED lamps show promise as an alternative low-energy light source.
The efficiencies of LED lamps are comparable to CFLs, but without the environmental problems from mercury inherent in CFLs.

As to induced "flicker", it is likely that the coatings applied to LEDs provide a smoother spectral output; however, it remains to be seen if this will be the case. It is likely that the "lower light temperature" bulbs (2700° or less) have a less "spikey" optical output.

Prices for LEDs varies widely. Recent Lowes and Home Depot prices varied between $6 to $9 to the $25 range for "40 watt-equivalent" (450 lumen) LED lights within a two-month period. Remote fluorescing LEDs, e.g., Philips L-Prize, had cost in the range of approach $40-$50 for an 940 lumen bulb, and Philips Ambient had cost nearly as much for an 1100 lumen bulb.

Fortunately, the costs of high quality LEDs are dropping. As of Nov-2012, Home Depot dropped the price of Philips L-Prize bulbs from $50 down to $30.

Despite these high prices, LEDs are becoming the illumination of choice for low intensity restaurant and retail illumination, as many of these businesses recognize the lighting quality issues of fluorescent lighting.

Are Fluorescents that Different?

The issue of spiked light output of fluorescent lighting was apparently known when fluorescent lights were introduced by GE circa 1938. [2]   At the time, the flicker effect was attributed to a line current (mains current) half-cycles (see pgs. 76-77 of the article).

More recent developments unrelated to fluorescents have generated substantial information, although research into neural response to fluorescent lighting is limited.

Comparison between Compact Fluorescent (CFL) and LED lamps
and between incandescent and LED lamps

While LEDs and fluorescent bulbs use fluorescent phosphors to render white light, the spectral patterns are quite different, as shown in the following graphs. Note (first graph) the spectral spikes, which are characteristic of all fluorscent lights. Almost all light output from fluoresents occur in these spectral spikes:

  The thin red line with the spikes represents the spectral output of the highly-rated EcoSmart CFL. The thicker orange and blue lines are spectral outputs of high-quality LED lights, with the blue line representing the output of the Philips L-Prize LED lamp (note the red peak at 625 nm). [3]

  This graph is on a different scale from the upper graph, so the red peak at 625 nm (yellow and green lines) on the lower graph appears much larger than the corresponding peak on the (blue line) on the upper graph. The fluorescent peaks, shown only on the upper graph (red line) are much more extreme, as can be seen by comparing the peaks on the red and blue lines in the upper graph. The spectral output of incandescent bulbs is depicted separately (probably because the magnitude of the extreme spikes of the CFL sample shifts the scale too far). On the lower graph, the grey and red lines represent incandescent lamps. The bulb represented by the red line is a GE Reveal incandesceent. Reveal incandescent and Reveal halogen incandescent bulbs use a neodymium glass to filter out yellow and other light in order to enhance the spectral output.) The yellow and green lines represent a Philips L-Prize LED lamp. [3]


Halogen lamps are not shown here, but have similar patterns to those of incandescent lamps, although a bit flatter.


Fluorescent lights have less adverse effects when mixed with daylight or ordinary incandescent light.
Some of the modern fluorescent lights with built-in electronic ballasts are supposedly better in this regard. The light quality is still poor, but the line current flicker is eliminated, which helps some people.

If you work in a fluorescent-lit room, get a different light.
Halogen floor lamps can be purchased for $35. Some can accept up to 300 watt bulbs (500 watts for the rheostat type, but they are no longer shipped with 500 watt bulbs for fire safety reasons).

At a workplace, it may be advantageous to say that the ballasts in the fluorescent lights are "worn out" or otherwise defective. The repair is available, but replacing of all these lamps is (perhaps) not economical. (Hence the floor lamp is saving the company a lot of money.)
(Actually some businesses have found that replacing the ballasts is economical because of costs savings in power used, service life of the tubes and long term replacement costs. Still the idea is to explain that the personal lamp is a way to save the company money -- which is true if one considers replacement of equipment in a single office.)
It turns out that the halogen lights are actually energy efficient. Consider a typical office workspace, with 2 fluorescent ceiling fixtures. (That's typically 4 tubes/fixture) 8 tubes at 40 w / tube, or 320 watts, plus about 10 to 30 watts for 4 magnetic ballasts.

Colour Temperature in Fluorescents

There is a very real possibility that colour temperature has a significant effect on sensitivity to fluorescent lighting. Fluorescent tubes and CFLs are commonly available at colour temperatures that range from 4100°K "cool white", or 5300°K, 6350°K and 6500°K "daylight", as compared to fluorescent lighting with a lower colour temperature 2700°K "warm white" or "soft white". (GE "Reveal" CFL bulbs, at 2500° would presumably have even less adverse effects on people with blue or blue-ultraviolet sensitivity.)

These preferred colour temperatures are 2700°K ("soft white"), with the GE "Reveal" CFL bulbs, at 2500°K.

"Cool" has a higher colour temperature than "Warm"

The nomenclature of colour temperature is a little bit contradictory because the old colour name nomenclature ("warm white" - "cool white") designations are the reverse of colour temperature designations. With the introduction of LED and consumer use of HID lighting, (numerical) colour temperature is becoming the standard:
Colour Name and Colour Temperature
colour code
(CRI ~85)
colour code
(super delux white)
(CRI ~95)
colour codes
color descriptor,
propriety name,
or trade
827 927 ww, wwx extra warm white 2600°K - 2700°K not common; close to yellow
830 930 ww, wwx warm white 3000°K close to yellow
835 -- w, wx soft white or warm white 3500°K  
-- -- -- GE Reveal fluorescent 2850°K used as delux lighting;
produces good quality fluorescent light
-- -- -- meat display 3200°K - 3800°K used as delux lighting;
produces good quality fluorescent light
841 941 cw, cwx
uw, uwx
Cool white 4100°K looks white
850 950 natural white;
natural white;
865 965 cool daylight cool daylight 6500°K bluish or purple cast
880 -- sky white sky white 8000°K SAD treatmemt
862 -- -- GroLux 6200°K 6400°K - 6500°K
may be better
-- -- -- plant growth -
(flowering stage)
2700°K - 3000°K (cannibus agriculture)
-- -- -- plant growth -
(vegetative stage)
5000°K - 6500°K (cannibus agriculture)
6400°K - 6500°K preferred
-- -- aquarium aquarium (fresh water) 10000°K  
-- -- -- blacklight
(lighting effects)
(365 nm)
-- -- -- blacklight
(350 nm)
-- -- -- blacklight
(insect traps)
(370 nm)
-- -- -- tanning (352 nm)
(UV-B 307 nm)
-- -- -- actnic (365 nm)
UV photocuring
diazo copying
-- -- germicidal low pressure lamp (253.7 nm)
no phosphors; hence not "fluorescent";
can cause injury if viewed

Table adapted from Wikipedia, which also has an explanation of the numerical colour code.

Colour temperature designations are the equivalent black body radiation. This system was used in the industry at least from the introduction of fluorescent lights by GE in 1939, and was identified in 1859.

"Almost Acceptable" Fluorescents

(Best Option if Fluorescents are the Only Option)

Anecdotal reports are that people sensitive to fluorescent colour will react to colour temperatures as low as 4100°K. This suggests that fluorescent lamps should be selected at the 2700°K range; specifically avoiding the 4100°K and higher colour temperatures.

If fluorescent lighting is used, it may be possible to request lower colour temperature lights. It is possible that this modification will reduce the adverse effects of fluorescent lights, at least for those individuals who have blue or blue-ultraviolet sensitivity. These preferred colour temperatures are 2700°K ("soft white") with the "927" designation.

The GE "Reveal" CFL bulbs and at 2500°K and GE "Reveal" tubes are the most optimum choice, and may even be as satisfactory as incandescent lighting.

The "red-blue pupillary flicker" effect can be exasperated by basic quality phosphor coatings (halophosphates) and triphosphor (80 series). Multicolour or "triphosphor deluxe" 90 series are likely to be less likely to cause adverse neurological effects.

GE has introduced a "Reveal" version of their CFLs and fluorescent tubes. Unlike their incandescent and halogen "Reveal" lights, which are blueish, the GE CFL "Reveal" line has a lower colour temperature -- 2500°K, although with less yellows. (The blue tint is the result doping the glass envelope with niobium, which is unnecessary in the fluorescent bulbes because the spectrum is controlled by the phosphors.) It is likely that these have an exceptionally broad spectrum of phosphors, reducing spectral peaks. The downside -- price. In 2012, prices were in the $11-$26 range (US) for 800-1500 lm.

"Meat display" fluorescent lights have been reported to have similar phosphor blends as GE "Reveal" lights; however, I found that they have higher colour temperatures (3200-3800°K).
Magnetic ballasts, common in many straight tube fixtures, should be replaced with electronic ballasts because the line frequency stimulates the red-blue pupillary flicker effect.

Workplace Accommodation

Avoiding fluorescent lights in the workplace presents its own set of challenges. For one thing, there's the issue of how to bring up the subject.
Bringing Up the Issue
The limitations here are
1. Doing so within the constraints of your disclosure of autism;
2. How much extra accommodation you wish to ask of your employer; and
3. The effect on others in the workspace.

1. "Within the constraints of disclosure"
Fortunately, sensitivity to fluorescents is widespread. Approaches can include:
- "Fluorescent lights bother me." (Note "bother me" is less medical sounding than "sensitive to". Being "sensitive to" crappy perfumes is seen as more acceptable than "sensitive to" something more related to neurology.)
- "I am sensitive to fluorescent lights." This is appropriate in some work circumstances, especially where one has exclusive use of the office or workplace. It has the advantage of implying a need for personal lighting for purposes of workplace accommodation. Again, sensitivity to fluorescent lights is fairly common.
- "I need the non-fluorescent lighting to avoid (migraines, vascular headaches, headaches, fatigue)."
This is generally regarded as a non-autistic issue:
search results for <fluorescent headache> 367,000 hits
search results for <fluorescent headache -autism> 310,000 hits ("autism" decluded)
search results for <fluorescent headache autism> 59,100 hits ("autism" included)
Despite this, fluorescent lights, including CFLs are almost universally considered objectionable by autistics.

2. "Extra Accommodation"
Normally "accommodation" only becomes an issue if the light is objected to. (No, don't bring in a gas light!) Most employers will permit an exception to the rule if the light is a form of workplace accommodation.

Halogen luminaires are objected to in some college dormitories. Most allow non-halogen lights, but if not, it may be helpful to obtain a medical note. (Using a conventional lamp fixture with a halogen bulb constructed in a standard "A" bulb configuration will generally go undetected.)
It's a good idea to place these things on power strips. That allows you to positively switch the light off at night, to avoid fire safety concerns. (You're more likely to find the power strip objected to in some large offices, in which case, you simply remove it, and possibly request an approved power strip.)

In many cases, the personal light is viewed as a type of decoration. A number of people use various types of lights in their offices. In my office, people enjoy the lighting from my halogen light. They just consider it a personal improvement, a little like fancy wheels on a car. They know I don't like fluorescent light, but there are no further issues.

A good reason to request that the lights be left off -- they're effectively broken and cannot be economically repaired. "The ballasts are 'worn out' or otherwise defective. Replacing all of these lamps would be uneconomical." The idea is that your personal light is a way of avoiding complaining.

3. Others in the Workplace
This applies of course to shared workplaces. Fortunately, most of the effects of fluorescent lighting can be mitigated by augmenting the fluorescent lights with incandescent lights. At one office I enjoyed for about 3 months (in an historic building), I used a pantograph-type desk lamp adapted to accept a 100 W halogen bulb. The overhead fluorescent lights were on when others were working there.

It may be possible to talk your employer into replacing the ballasts with electronic ballasts, but except where a safety issue is involved (see below), the employer may object to the extra cost. (On the other hand, if the employer is for some reason already viewing the fluorescent lights as a problem, it may be worth suggesting the replacement of the ballasts as a "cheap alternative".)

Safety Issues

A separate issue is the safety of fluorescent lights in workplaces which include machinery. The flicker can create a strobe effect which can make it possible for a worker to accidentally get caught in moving parts. Since this is most likely to occur when the worker is distracted, fluorescent lights are dangerous near moving machinery.

This safety problem is readily solved by the replacement of old style ballasts with electronic ballasts. Advantages include longer life of the fluorescent tubes, as well as avoiding workplace accidents. Some employers appreciate having this pointed out, although others will regard safety suggestions with suspicion. (Most large employers encourage such safety suggestions, and a suggestion combining "safety" with "cost savings" is regarded favourably.)

Some machinery includes warnings concerning operation with fluorescent lighting, which means that the electronic ballasts improve workplace efficiency.

Another advantage to replacing ballasts is that the electronically ballasted fluorescent lights are less likely to interfere with optical timing equipment and similar devices.


Be aware of situations where you may have problems.
Closed rooms with fluorescent lighting would be an example.

If you know you'll be sleepy in a particular environment, have some coffee.

Other Optical Issues

This ranges from excess light to monitor flicker
Wear sunglasses or Irlen lenses
Irlen lenses are colour-matched to the individual's optical sensitivity as determined by testing the individual.

"For months I've been wanting to ask the question, 'Where are you, Al Gore?' You can only polish that Oscar for so long. And the Nobel was decided by Scandinavians! I don't blame you for not wanting to enter the viper pit again after you already won. But getting us to change out our incandescent light bulbs for some irritating fluorescent ones isn't going to save the world. All it's going to do is make us more agitated and jumpy and feeling like once we get home we haven't really left the office. - Michael Moore, 2-Jan-08, commenting on the US Presidential candidates.


[1]^       Daniel Stern Lighting, Blue Bulbs
        Illegal Blue Bulbs

[2]^       G.E. Inman, Characteristics of Fluorescent lamps Thirty-second Annual Convention of the Illuminating Engineering Society, Minneapolis, Minnesota, August 29-31, 1938. Author: Lamp Development Laboratory, General Electric Company, Cleveland, Ohio.

[3]^       www.molalla.net/members/leeper/L%20Pr ize%20Bulb/L%20prize%20bulb.htm - description and evaluation of Philips L-Prize bulb with measurements by Doug Leeper. -- This article includes comparisons of spectral output of the L-Prize LED bulb, a TCP brand CFL bulb and incandescent bulbs. Of note, it compares the spiked output of TCP's CFL bulb (CRI=82; 2700 °K), incandescent bulbs including Reveal neodymium glass incandescent bulbs, and two of Philips' "next generation" LCD bulbs.

back to "etc."
back to "Workplace Accommodation"
back to Relationships index

First posted 11-Jan-03, and 5-Aug-07 as a separate page. Last revised 06 Mar 13.

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