The Trade Off
Does it mean that the potential of mercury vapor lamps to cause debilitating effects on health could turn out to be its stumbling block in its wide scale usage? To set things in perspective, they indeed are filled with mercury and it does not simply disintegrate but continues to have a vestigial presence. Discarded bulbs which have lost their glow may be buried deep inside the surface soil and the mercury could continue to leech into the soil as well as adjoining water bodies, affecting the health of the human beings who are dependent on the soil for produce or drinking water.
It also needs to be underlined that mercury is not the only evil in the mercury filled lamps, but other chemicals present in the bulbs have the potential to cause sufficient damage to health.
Since the light emitted by a mercury-vapor light has a blue tone, this needs to be accounted for, or color- corrected as it is called. This rectification is done by applying phosphor on the inner surface of the bulb. Most modern mercury vapor lamps have this rectification done in them. If you remember the acronym VIBGYOR, you will see that since mercury light is more towards the blue end of this spectrum break up, it lacks in the red end. This is taken care of by adding phosphor, but then this red emission keeps increasing over a period of time due to the presence of the continuous radiation effect. This radiation is certainly detrimental for the health of human beings as well as any pet animals in the house.
Such lamps have been used for purposes such as street lighting since the late 1940s though the modern version of these lamps is much better than they were then. Most governments, especially in the US and EU, are passing regulations against the use of such lamps. In fact they would be barred in the European Union in 2015, while the US has put a ban on ballasts and fixtures since 2008. Still it might take quite some time before these are stopped from being manufactured or used in most other parts of the globe. In such a scenario the onus of protecting the health has to vest with the manufacturers. It needs to be emphasized that all manufacturers should insist that they do not allow any ultraviolet light to escape from the lamp enclosures. The adjacent figure shows the constructional details of a typical mercury vapor lamp with all parts are labeled clearly.
Image Courtesy: Lamptech, UK