Praseodymium oxide is found in didymium glass, along with neodymium. Didymium was originally regarded as a single element, and it was 30 years after its original discovery before it was determined that it in fact contains two elements, praseodymium and neodymium. Didymium glass is used in eye protection for welders and glassmakers, as it blocks specific wavelengths of light without impairing overall vision.
Aircraft engines can also contain some praseodymium, as it’s alloyed with magnesium in small amounts to make high strength metals which are used in them.
Some types of fibre optic cable made of fluoride glass also have praseodymium added to them in small amounts, as it can act as a signal amplifier.