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Printed Electronics World
Posted on June 7, 2007 by  & 

But Edison's Lights Are Still Working

Compact fluorescent bulbs bring problems

Edison's original incandescent lamp bulbs were recently sold as collector's items. They still work. Contrast the one year declared life on many of today's lamp bulbs. Mankind got to the moon forty years ago and Edison must be turning in his grave.
We are led to believe that the incandescent bulb will now be consigned to history because of the more efficient "compact fluorescent" CF option. Certainly this uses far less power and it will therefore cause less global warming. When enthusiasts are told of fact that these bulbs contain mercury, they point out that they reduce the amount of mercury emitted by coal fired power stations by a larger amount per bulb.
However, countries such as New Zealand and Switzerland use wind turbines and hydroelectric schemes to generate their power. France and other countries have a large contribution from nuclear power and none of these options emit mercury. Where mercury is emitted by coal burning it is over a vast area so little falls in one place. In contrast to this, when mercury containing bulbs are trashed they enter a small area of landfill and drop mercury straight into the local water table.
CF bulbs are a very flawed interim stage. Their so-called ten year life is not experienced by many users, who find that they darken unacceptably or fail long before that. Armin Reller, a chemist at the University of Augsberg in Germany calculates that the terbium used in CF bulbs could run out by 2012, for practical purposes. Meanwhile, the richest current commercial sources of terbium are the ion-adsorption clays of southern China.
Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate, materials that are used in solid-state devices. It is a crystal stabilizer of fuel cells which operate at elevated temperatures, together with zirconia.
Terbium is used in alloys and in the production of electronic devices and its oxide is used in green phosphors in fluorescent lamps and colour television tubes. Sodium terbium borate is used in solid state devices and its brilliant fluorescence leads it to being used as a probe in biochemistry.
Terbium green phosphors (which fluoresce a brilliant lemon-yellow) are combined with divalent Europium blue phosphors and trivalent europium red phosphors to provide the "trichromatic" fluorescent lighting technology, which is already by far the largest consumer of the world's terbium supply.
OLED and electroluminescent to the rescue?
Clearly we must hope for printed laminar ac electroluminescent and OLED lighting to improve in lifetime and become generally affordable for lighting. They will not incur the expense of massive power factor correction at the power station, as happens with compact fluorescent bulbs, and they will not contain mercury or other dangerous substances. They do contain other rare metals but work is proceeding to replace these. The question is whether they will have acceptable life.
Konica Minolta has achieved 10,000 hour lifetime with OLED lighting at 64 lumens/watt and 1,000cd/m2 with a small area of OLED, using optical enhancement. However, it is difficult to say who is in the lead because there are no commonly used standards for testing OLED lighting. All we can say is that it is probable that this is one of the best results so far.
Will some of the pioneering OLEDs be sold as working collector's items in one hundred years from now when OLED lighting in the shops has One Year Life written on it? Let us hope not.
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