LEUCO DYES

Thermochromic Leuco Dyes (LD's) change color with temperature.  LD's change from colored when cool to clear (no color) upon heating.  LD's are reversible, or change color back and forth as the temperature fluctuates.  It takes about a 5ºF (3ºC) temperature change for the LD to change color.  They are available in 15 different colors and a wide range of temperatures.  The Leuco Dye products are available in a wide variety of forms, including powder, slurry, water-based ink, epoxy, master batch, etc.  

LD's are more robust and less expensive than liquid crystals and can be used in a wider range of inks, plastics, etc.  Because LD's are not very sensitive they do not make accurate thermometers, but are used in applications where larger temperature differences are present or when temperature accuracy is less important.  Some popular LD applications are the Duracell^® batter tester, Nerf^® football, and Hungry Jack^® microwave sensor.  The Duracell^® battery tester indicates the remaining power left in the battery.  The Nerf^® football is purely a novelty item that changes color when touched by your hand.  The Hungry Jack^® microwave sensor indicates when the syrup had been warmed to the right temperature in your microwave. 

A LD's life span is adversely affected by sunlight, extreme temperatures, and contact with aggressive solvents.