Fluorescents-4A: Flicker and UV

This is the fourth post in a series about compact fluorescent lights (CFL).  We look at a number of different issues that have been raised, some may be true problems, some almost certainly are not “show stopper” issues.  CFLs will be our lest expensive choice for bright light bulbs in the U.S.,  starting January 2012.

The first post discussed mechanical longevity of the CFL bulbs; the second discussed frequent switching and what it does to the estimated life time costs of these very expensive bulbs;  the third discussed the loss of intensity as the bulb ages or as the temperature changes from its optimum value.   Here, we look at 2 concerns, lamp flicker and UV emission.  Part 4B will look at lamp color and environmental issues.


Fluorescents have had a bad reputation because they rapidly blink on and off, sort of like a motion picture image.  The reason is that fluorescent lights go dark when the driving voltage is zero.  The blinking was too slow, and some people get/got massive headaches when working under fluorescent lights.  This was such an issue that during the last decade, many state electrical codes were changed to specify the maximum ripple in brightness that would be allowed for a fixture.

All this was due to the magnetic ballasts (that also need starters) in use until just recently. Power line AC voltage goes to zero 120 times a second (North America) 100 times in other places (twice line frecuency) and magnetic ballast output goes to zero is sync with the power.    Incandescent lights does not display this problem because the glowing filament stays hot and emitting, even during the millisecond or so when little or no heating current flowed.

With the generation of tubes and bulbs released in the past 5 years, the magnetic ballast was superseded by the electronic ballast.  In these circuits, the switching frequency is 40 thousand times a second or higher.  Human response is much slower than 40 kHz,  and to the best of my knowledge, no one gets headaches anymore.

Ultraviolet light  (UV)

UV radiation from fluorescents is well known.  Here is a 2008 Oct 09 report on this topic by the UK Health Protection Agency, copyrighted in 2011 .  You occasionally will run across warnings about exposing plastic and rubber items to prolonged CFL exposure. Read How Fluorescent Lights Work.

Voltage supplied to an FL tube does two things.  1.  It causes electrons to boil off due to the heated filaments. 2.  It accelerates the electrons through the mercury vapor, exciting the atoms to emit UV light which is the principal emission from the tube.  The UV is absorbed by the phosphor layer on the inner walls of the tube and (lower energy) visible light is emitted into the external world.

If the phosphor layer is too thick the visible light can not get out of the tube.  If it is too thin, bright visible light will be generated, but a significant intensity of UV will be allowed to escape into the room.   The manufacturer’s tendency is to make the layer thin, to save costs.   If the tube was not pre-cleaned properly,  even thick phosphor layers will not adhere to the glass wall and spots will appear where the UV can freely escape.

CFL-Sunglasses_imgUnderstand, this ought to be an issue primarily for those with UV sensitivity.  But … if the bulb has been manufactured with little regard to the end user, we will find batches of dangerous bulbs with even visible holes in the white coatings, UV spigots anywhere along the tube.  Note that most tubes/bulbs are made in China.  What kind of inspection does your country do for imported fluorescent lighting?


click for a list of LastTechAge posts on illumination technology

My main worry in all these posts is that all our fluorescents appear to be made in China.  Here is a wonderful opportunity to rake in the profits for the plant owners –  those people who were young ideologists during the Great Leap Forward years, the leaders of the gangs who intimidated the populace.  We will see many really cheap bulbs and great confusion.  I suspect that we will see in upturn in UV related health issues that will be blamed on solar exposure.    The other issue, flicker, is now dead; fast response by industry since state regulatory laws are themselves only perhaps 5 or 6 years old.

Stay tuned.  Next time, same place same blog, we will look at mercury and other environmental contaminates

Added In Final Proof:   The New York Times had an interesting article this morning (Thursday, 2011 Aug 11) in their HOME section.  Bob Tadeschi (The Pragmatist) writes it is about time to change lights.  He has a number of points, one is that only the 100 W bulbs cannot be sold after the start of 2012 and final phase out of our incandescent history will take 2  years to complete. Another of his points is that you can easily buy cheap bulbs that don’t do not’n’.  He says brands are very important (“very” is my adjective) and CFLs can be disappointing and very confusing, considering the many different types you would need about the house.   He does say these things will last maybe longer than you are in your house, but did not add that you must buy the most expensive brands and must be willing to live in a house with significant light dimming to accomplish this.  He does talk about the other options to meet special needs (that are much more expensive right now).  All in all, a good article to read!

Charles J. Armentrout, Ann Arbor
2011 Aug 11
This is listed under    Technology   …thread   Technology >  Fluorescents
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About LastTechAge

I am a physicist with years of work in fusion labs, industry labs, and teaching (physics and math). I have watched the tech scene, watched societal trends and am alarmed. My interest is to help us all improve or maintain that which we worked so hard to achieve.
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