Are flourescent lamps efficient
I have been asked a few times lately if it is better to leave fluorescent lights switched on as they use so much energy to start up? And, are fluorescent tubes (and by extension compact fluorescent lamps – low energy lamps)really efficient?
Fluorescent lamps, be they standard strip lights or compact fluorescents, use gas discharge technology and it takes 3 to 15 minutes (depending on the type of lamp) to vapourise the gas, get up to temperature and reach full luminosity. It takes no extra power to do this, just a bit of time. So the argument for leaving lights on relates to time rather than energy. If you are popping in and out of a room all day you probably want to leave it on. Otherwise turn it off. To put it simply a light left on uses more energy than a light turned off.
Fluorescents are more efficient than incandescent lamps by a factor of about 4. To be technical, they produce around 90 lumens per watt compared to about 20 watts for incandescents (these figures vary with the type of lamp but are broadly accurate). It is why incandescents have been banned in Australia and are being phased out here. They give a different quality of light, which is what leads to the idea that they are not as bright and therefore you need more of them. My Grandma said the same when her gas lamps were replaced with nasty electric bulbs, but she got over it.
While we are on the subject, I have also been asked if fluorescents have nasty chemicals and gases in them, and the answer is yes! They have 5mg of mercury in a 40w tube. It is a tiny amount, less than the size of a pin head – but poisonous nonetheless. They also have a phosphor coating to the glass (which is what fluoresces and produces the light) which is not pleasant, but not poisonous. The gas in the tube is usually argon which is inert and harmless.
There are new lamps about to hit the market that use xenon gas – no mercury and no phosphors – which are even more efficient. These will produce over 120 lumens per watt.