The light thermometer is the most accurate device of its type in the world. Amazingly, it uses visible light to measure temperature. 

Developers are referring to the new device as a nano-Kelvin thermometer. Degrees Kelvin is the same as degrees Celsius, but starting at -274 degrees C. below zero.

University of Adelaide researchers created the new device, which is three times more accurate than any other thermometer. The invention from Australia is capable of measuring temperatures to one 30-billionth of a degree Kelvin in one second.

"To emphasize how precise this is, when we examine the temperature of an object we find that it is always fluctuating. We all knew that if you looked closely enough you find that all the atoms in any material are always jiggling about, but we actually see this unceasing fluctuation with our thermometer, showing that the microscopic world is always in motion," Andre Luiten, project team leader, said. 

The light thermometer shoots beams of red and green light into a precisely-manufactured crystal. Red light travels more slowly than green, and the effect is more pronounced as the crystal warms. This is caused by thermal expansion of the crystal, providing a longer path going around the structure. 

"By forcing the light to circulate thousands of times around the edge of this disk in the same way that sound concentrates and reinforces itself in a curve in a phenomena known as a 'whispering gallery' - as seen in St Paul's Cathedral in London or the Whispering Wall at Barossa Reservoir," Luiten told the press. 

Measuring the difference in the time it takes each beam to travel through the crystal, allows the device to calculate ambient air temperature. 

Researchers believe the light thermometer could easily be adapted to measure other environmental effects, including air pressure, humidity or to search for the presence of a particular chemical. 

Unlike traditional thermometers, this new invention does not measure absolute temperature, but changes in environmental conditions. The same team that designed the new light thermometer previously created extremely accurate clocks. Although these could measure increments of time precisely, it was similarly incapable of recording absolute time. For the thermometer, this drawback may not be much of a challenge bringing the device to the mass market. Many industrial applications simply require temperatures remain steady through the production process, a feat light thermometers could easily fulfill. Such thermal stabilization devices could also prove invaluable for medical researchers 

Development of the light thermometer is profiled in the journal Physical Review Letters.