Sight fears over low-energy bulbs

[RenewableCandy]

As a partially-sighted migraine sufferer I can categorically state that the whole CFL lightbulb scare thing is pure bollocks.

However as a Honiton native I must also add that if you must read or do close work, for heaven's sake make damn certain that you have enough light.

[Adam1]

The amount of mercury in compact fluorescents is less than the additional mercury that goes up a coal power station's chimney as it generates the additional electricity to run an incandescent bulb. Also, the mercury from coal burn freely enters the environment whereas the majority of the smaller amount in CFLs remains in its sealed glass container.

I've been trying to quantify this. It seems that each bulb contains a maximum of 5mg of mercury (according to www.lightingassociation.com and www.elcfed.org). If we take a typical 15W CFL replacing a 60W GLS (incandescent), saving 45W over 10000 hours, it will save 450kWhs over its life. How much additional mercury is emitted as a result of producing 450kWhs from the UK grid?

[biffvernon]

Surely the important question is whether digging mercury out of the ground and either scattering it about via power station stacks or putting it in little globs in landfills is actually a hazard.

[Adam1]

Surely the important question is whether digging mercury out of the ground and either scattering it about via power station stacks or putting it in little globs in landfills is actually a hazard.

Absolutely, Chris's other point, that CFL mercury is relatively contained still stands. I'm just curious if it could be quantified. How many orders of magnitude does the generation of the extra electricity produce in mercury? Is there a source for this?

[clv101]

If a CFL last 10,000 hrs and uses 25 W and an incandescent uses 100 W it saves: 75 x 10,000 = 750 kWh of electricity or 2700 MJ.

Anthracite is 32 MJ/kg, Bituminous coal is 24 MJ/kg - call it 30 MJ/kg.
As a rough approximation lets say the power station/electricity transport is 30 % efficient so we get 9 MJ/kg of coal.

2700 / 9 = 300 kg of coal saved per CFL.

A Google books link says bituminous coal contains 0.07 mg of mercury per kg. Lignite is higher at 0.12 mg and sub-bituminous is lower at 0.03 mg. It then goes on to cite 2003 data saying that on average coal has 0.2 mg/kg and may be as much as 1.0 mg/kg.

Amazingly, soil near a coal power station can have levels between 0.3 and 0.5 mg/kg depending on the pollution control technologies employed. The soil ends up with as much mercury as the coal!

Let's assume 0.2 mg/kg, therefore our CFL saves 60 mg due to the 300 kg of coal saved.

This website, link, says:

The average CFL bulb manufactured today contains 4mg of mercury.

So the extra coal burn deposits 15 times more mercury in the surrounding farmland as the CFL contains in its fairly robust glass container.

25 W is quite a powerful CFL and maybe 10,000 hrs is optimistic. A 15 W lamp replacing a 60W, with lifetime of only 5,000 hours saves 90 kg of coal and 18 mg of mercury. Assuming it still contains 4mg of mercury, the ratio falls to 4.5 time.

So, the rough, average, ball-park figure is that using incandescents releases ten times as much mercury into the environment as CFLs contain, realising that only a fraction of this contained mercury will end up released into the environment.

[biffvernon]

Where it is released does seem important. Power stations scatter it over farmland soils, CFLs concentrate it in landfill (and Could potentially be recycled if we developed a light bulb recycling machine).

That makes the mercury case in favour of CFLs pretty strong.

Now we just need to know what the hazard of the soil contamination actually means in health terms?

[Adam1]

Thanks for that Chris and Biff

Of course, coal is only about 35 - 40% of our generating mix. Presumably, there are no mercury emissions from gas or (?) nuclear. If that's the case, putting aside the point about scattering/concentration in a landfill, we are still looking at 3 or 4 times the mercury with incandescent, here in the UK at least.

I wonder how difficult/energy intensive it would be recover the mercury and other chemicals after use, or whether they could be refurbished. There ought to be minimum standards for the longevity of CFLs. Plus, wouldn't it be great if they were modular, so that when it stops working, you could just replace the tube and keep the ballast? (As I believe the latter last about five times as long as the former.) It wouldn't help the mercury issue, but it would reduce further the embodied energy.

I'll take my anorak off now.

[clv101]

Of course, coal is only about 35 - 40% of our generating mix.

Oh yeah!

The 35-40% mix isn't the right fraction to use though. Nuclear output for example would be identical if we used all CFL or none. We have to work out which fuel is used for marginal electricity demand from incandescent lighting.

I think the base load incandescent lighting would be covered by coal and the deviation load at peak would be covered by gas. Gas and coal and approximately the same so all we really need to know is what the incandescent lighting base load is.

This is where it gets a bit more interesting as I expect most incandescent lighting isn't base load at all - so doesn't run on coal at all. We need to get time/demand curves for different types of load and time/fuel curves for different types of generation.

[Adam1]

Wow, it's interesting how often digging into the detail of an issue reveals less clear cut answers.

As you say, it is probably hard to say accurately whether lighting draws predominantly from baseload but, from memory, lighting is up to 30% of the commercial & industrial sector's energy demand. That demand will (or should) mostly be during the day (i.e. largely or wholly non-coal based generation?) However, most lighting in this sector is probably already fluorescent based.

Lighting in the residential sector is only about 10% of the sector's demand but it should mostly be during the hours of darkness. So probably a bit more coal in the generation mix. But given that commercial/industrial demand is greater than residential, very little extra coal is being burnt as a result of running incandescents.

So the mercury issue probably boils down to how we manage the waste from CFLs. I think that the EU have stipulated that CFLs should be handled as special waste. Certainly, when I lived in Hackney (E. London) the recycling scheme included CFLs. Presumably, they are processed in some way to control the spread of mercury. If we are going to get into Cradle-to-Cradle manufacturing, we should be ensuring that mercury and all the other finite elements (phosphors?) are not dispersed into the environment.

[biffvernon]

This is pointing towards coal-emitted mercury being a bit of a red herring then to the CFL debate.

Certainly, when I lived in Hackney (E. London) the recycling scheme included CFLs.

How did that work? I guess if CFLs went into the recycle wheeliebin a lot would be broken before they got near the sorting plant.

[Adam1]

This is pointing towards coal-emitted mercury being a bit of a red herring then to the CFL debate.

Certainly, when I lived in Hackney (E. London) the recycling scheme included CFLs.

How did that work? I guess if CFLs went into the recycle wheeliebin a lot would be broken before they got near the sorting plant.

I must say, I don't know. We had recycling boxes, rather than wheelie bins. I guess Hackney hoped or assumed that people would put their CFLs in some sort of container.

Thinking about it more, even though coal stations disperse mercury locally in the soil, it is contained within a few hundred metres of the plant. CFL mercury, although it is not atmospherically dispersed, is geographically dispersed. Therefore it is harder to control what happens to the 'waste', as responsibility for it rests with many people.

Also, apparently according to the reference Chris gives above, coal stations fitted with flue gas desulphurisation (most or all in the UK?) have 40% lower mercury emissions.

Given also that mercury production peaked in the 1960s (according to a 2007 TOD article), there are good depletionist reasons for finding ways to capture the mercury or for developing a different lighting technology (perhaps LEDs).

[skeptik]

However as a Honiton native...

LOL... Honiton, Heart of Darkness?

Is there something special about that particular part of deepest, darkest Devon? (normally bypassed at 70mph on the A303 en route to Cornwall)

[RenewableCandy]

However as a Honiton native...

LOL... Honiton, Heart of Darkness?

Is there something special about that particular part of deepest, darkest Devon? (normally bypassed at 70mph on the A303 en route to Cornwall)

Yes there is. Honiton is famous for its lace-making. Very detailed close work mostly done by 12-16 y.o. girls, in candle-light, for far too many hours in the day. You can guess what that did to their eyesight...

[biffvernon]

Also, apparently according to the reference Chris gives above, coal stations fitted with flue gas desulphurisation (most or all in the UK?) have 40% lower mercury emissions.

Does that mean that the mercury stays with the sulphur, which is used to make calcium sulphate - gypsum - and ends up in the plasterboard of our homes?

[Adam1]

I presume that it means the mercury is captured...a subject for more study!