No. 104 - Miljøstyrelsen

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fluorescent lamp furthermore contain an inert gas (e.g. argon) under low
pressure and the glass tube is coated on its inner side with a thin layer of
fluorescent phosphor (www.datalyse.dk).
When the glass tube is subjected to voltage the electrode is heated and
electrons are released. The temperature in the tube increases and the mercury
evaporates further. When the free electrons hit the mercury atoms the latter
exite, i.e. are lifted to higher energy levels. Exited mercury atoms will decay
after a certain time and thereby emit ultraviolet light together with a small
amount of visible light. The ultraviolet light is converted into visible light
when it hits the phosphor coating on the inner side of the tube (Aucott et al.,
2003; www.datalyse.dk).
According to information from one of the interviewed manufacturers some of
the mercury will in its decay be bound to the glass and the phosphor coating.
The amount of bound mercury will increase with the lifetime of the lamp.
Normally this can be seen by the inner side of the glass and the inner
phosphor coating turning grey. The areas near the electrodes will turn black
with time.
According to Truesdale et al. (1992) mercury will probably also be found in
metal form in used compact fluorescent lamps/straight fluorescent lamps,
since the inactive atmosphere in the tube should prevent significant oxidation
of mercury.
1.3 Relevant legislation - RoHS
According to the RoHS Directive 2002/95 (Restriction of the Use of Certain
Hazardous Substances in Electrical and Electronic Equipment) mercury in
compact fluorescent lamps is exempted from the rule on a maximum content
of 0.1 % in homogeneous materials. Maximum permitted mercury content in
compact fluorescent lamps is 5 mg/lamp. For straight fluorescent lamps
maximum permitted mercury content depends on the lifetime of the
fluorescent tube and the type of phosphor coating on the inner side of the
tube. For ”halophosphate” 2 permitted amount is 10 mg/lamp, and permitted
amount of triphosphate 3 is 5 mg/lamp for normal lifetime and 8 mg/ lamp for
long lifetime (RoHS EU, 2002). For compact fluorescent lamps and straight
fluorescent lamps complying with European ecolabel criteria the mercury limit
value is 4 mg/compact fluorescent lamp or 5 or 8 mg/straight fluorescent lamp
depending on the lifetime (EU, 2002). See Table 1-1.
2
According to dataanalyse.dk the most common halophosphate compound is calcium
fluorophosphate Ca F(PO ) .
5 4 3
3
According to dataanalyse.dk rare soil types and, often, four to five different
phosphates are added to obtain better colour value.