In the Limelight
In 1825, Thomas Drummond heated a ball of lime in front of a reflector, creating a brilliant white light. The discovery led to improvements in theater and lighthouse lighting.
To be ‘in the limelight’ means to be in the spotlight or to be the centre of attention, but why ‘limelight’? The phrase comes from the theatre in the days before electric ighting. At this time there was no simple way produce a bright, white light suitable for a stage spotlight – gas flames were far too dim.
However, in the 1820s one Goldsworthy Gurney (later ‘Sir’) found that if he played a hydrogen-oxygen flame onto a cylindrical lump of lime (calcium oxide) he found thathe lime glowed with a brilliant white light. With appropriate lenses, a beam of light could be produced which was suitable for theatre spotlights and also lighthouses. he two gases were stored in bags or bladders and were fed to the burner under pressure caused by placing weights on the bags.
A little later a Scottish Engineer called Thomas Drummond saw a demonstration of this light and developed it for surveying – the light was bright enough to be visible for ver 60 miles and a light placed on one hill could be seen by a surveyor on another hill many miles away.
What causes limelight? In fact almost anything heated up to a high enough temperature will glow white hot. This is called incandescence. Calcium oxide (lime) is suitable because it does not decompose at high temperatures, it does not react with oxygen in the air (it is already an oxide) and it has a very high melting point (3123 K,285O oC). When an object is heated to a high temperature, electrons are promoted from the ground state to very high energy levels. They then drop back to a whole variety of lower energy levels, each transition giving out electromagnetic radiation of a different wavelength (colour). The resulting mix of colours corresponds to white light.
Visit RSC to read more about limelight.
Excerpted with permission, www.rsc.org.