Perhaps a good place to start is with fluorescent light bulbs and how foolish it was to ban incandescent light bulbs in the first place.
Lets start with what everyone has been told about fluorescent light bulbs. Fluorescent light bulbs require less energy, produce more light and last longer than an incandescent light bulb. That much I think everyone knows so I don't intend to belabour the point.
The point that not many people are aware of is that they contain mercury. As a first year physics TA, one of my more enjoyable labs was showing the spectrum of light from a fluorescent light bulb and having them guess what element (from a set of four elements) the light spectrum was from. Incandescent lights work by heating a metal filament and hence have a continuous light spectrum, that means if one was to separate the light into all its component colours it would contain all of them. Fluorescent lights, because they involve a process of excitation and emission from mercury (followed by fluorescence which converts the emitted radiation into visible light) instead has a light spectrum composed of many lines. You can actually make your own spectrometer out of a CD and prove it to yourself.
Returning from my original train of thought: mercury! I think its widely accepted that mercury is hazardous so I won't dig up the Material Safety Data Sheets (MSDS) for it to highlight my point.
Fluorescent light bulbs generally contain only 4 mg of mercury. That doesn't seem like a lot, and especially if you consider that those mercury thermometers that we used to use have up to 1000x the amount of mercury. But America uses millions of light bulbs every year, and far fewer of the mercury thermometers. Moreover, many people are still not aware of the proper disposal methods of fluorescent bulbs throwing them away just like they tossed their old incandescent bulbs in the garbage bin.
Landfills may have all kinds of protection to contain hazardous gases and liquids but there's a long way between your garbage bin and the landfill and a lot of workers that may be exposed to the mercury if the bulb breaks en route.
The last point I'll make is this. Per any set unit of time the fluorescent light bulbs consume less energy but if people, accepting this to be true, use fluorescent light bulbs longer then the net benefit decreases.
So in short, there is nothing wrong with fluorescent light bulbs from a scientific point of view. The problem lies in human behaviour towards them and if we fail to inform the public adequately concerning the risks and proper handling methods for these materials then banning incandescent bulbs will cause more environment problems than we solve.
A Watt is most often understood in the context of a light bulb. We all know that a 100W light bulb is brighter than a 60W one, and logically that the 100W one will consume more energy. However, the unit Watt is more a unit of energy consumption. So for example, the horsepower of can be converted to Watts. Moreover, the rate of energy you consume walking up the stairs can also be written in units of Watts.