The fact that many of us are dealing with linear or compact fluorescent lamps on an almost daily basis makes it very easy for many people to take them for granted and overlook their inherent complexity. But this complexity in design and manufacturing can have a major impact to on the way these light sources need to be treated at the end of their life – and should inform the specification process at the beginning of their life.
Although many BSEE readers will already be aware of the structure of these lamps, it’s worth taking a quick look at the basics – and what’s changed in recent years. Essentially there are two main elements to a fluorescent lamp of any kind. There is the gas-filled glass tube which is coated with phosphor powder on the inside and the control gear. In a linear fluorescent lamp the tube and gear are separate; with compact fluorescent they may either be separate or integrated into a single unit.
The control gear controls the electrical current which passes through the mercury vapour in an argon or neon gas in the tube, causing it to emit ultra violet light. This in turn excites the phosphor powder so that it fluoresces, producing the visible light that we see from the lamp.
With CFLs one of the more challenging aspects is to provide a sufficiently large light-emitting surface area within a small space. The tubes also have to be positioned so they don’t block the light from each other. The fact that CFLs have got progressively smaller is a combination of more efficient phosphors and improved manufacturing techniques.
Another development has been in the production of the mercury vapour in the tube. Traditionally, the mercury was inserted into the tube as a liquid and over the life of the lamp some of that mercury would be absorbed into the phosphors, glass and electrodes. This was true for early linear and compact fluorescent lamps and is still the case for lower quality products.
Most manufacturers, however, now use a solid mercury amalgam rather than liquid mercury. Because it’s solid, this is a much safer option and also means that less mercury needs to be used in manufacture.
Nevertheless, this does mean that all fluorescent lamps contain mercury and, because of this, they are classified as hazardous waste. Clearly, this has implications for how they are dealt with at the end of life. As electrical items they are included in the Waste Electrical & Electronic Equipment (WEEE) Directive so have to be sent for recycling rather than to a landfill site. In addition, because of their hazardous nature, they need to be dealt with by specialist contractors – or taken to a local council recycling centre in the case of low volumes.
Once they enter the waste stream, the various components of the lamps have to be separated from each other. For example, if the glass is to be recycled, the phosphors have to be stripped off. And, as noted earlier, these phosphors will have been contaminated by mercury so this needs to be distilled from the phosphors by heating to around 8,000°C. At the same time, any ferrous and non-ferrous metals are reclaimed and also sent for recycling.
These procedures, while still complex and requiring specialist equipment, are easier where the control gear is separate from the lamp. In the case of CFLs with integral control gear, all of these components need to be separated from the casing.
Once all of the components have been separated, it may be possible to re-use the phosphors in the manufacture of new tubes, and the mercury may be re-used in lamp manufacturing or for other purposes. Similarly, the recovered metals may be recycled in a number of ways. As a result, a large percentage of each waste lamp is recycled – so that when dealt with properly, used fluorescent lamps have very little impact on the environment.
Clearly, then, anyone who is involved in the disposal of these light sources – perhaps in a project management role – has an important role to play in ensuring they are consigned to the waste stream in the right way. In addition, there are obvious benefits to recycling CFLs that are inherently more recyclable. It’s worth noting that those brands that place environmental issues at the top of their agenda have made major advances in improving the recyclability of their products.
As a result of all of these factors, there is a very strong case for considering all of these factors at the early design stage and ensuring they are addressed in the specification. In fact, I would suggest that this approach to make life easier for the end client is an essential part of the specifier’s role.