Argand went on to design a lamp that represented the greatest breakthrough in lighting technology for 2,000 years. A glass chimney protected the flame and, more importantly, increased the draft of air that fed the burning oil. Hot combustion gases would rise up the chimney, pulling fresh oxygen over the wick, thereby reducing smoke and soot and significantly increasing the flame's brightness. An Argand lamp was as bright as seven candles.
The Stevensons employed the Argand lamp in many of their lighthouses, and also pioneered the use of lenses, reflectors and rotating mechanisms to enhance the brightness of the beam. As well as making engineering changes, they also implemented operational changes to Scottish lighthouses. Traditionally, lighthouses were run by pairs of keepers, but Robert Stevenson, the senior member of the lighthouse dynasty, demanded three keepers per lighthouse. His policy was inspired by a tragic incident that occurred at the Eddystone lighthouse when only two keepers were on duty. "One died, and the other, for fear of being suspected for murder, kept the corpse of his companion for about four weeks," reported Stevenson. "When the state of the weather permitted the attending boat to go off to the lighthouse, the poor man was found sitting upon the Rock. The body of the deceased was in such a state of putrefaction that it was long before the effect of it left the apartment of the lighthouse." In short, Stevenson favoured three keepers in order to remove suspicion of murder if one died.
This month marks one year without British lighthouse keepers. There were once 300 keepers, but they have now been replaced by a bank of computers in Harwich that monitor the generators, burglar alarms, fire detectors, radio beacons and satellite equipment in each lighthouse. The computers are run by two operators per shift: presumably the risk of being driven to insanity and murder is smaller during an eight-hour shift in Harwich than during an eight-week shift on a remote rock in the Atlantic.