Square or rectangle cuvets and cells hold a sample, often a substance dissolved in a solution, and are placed in a spectrophotometer for testing. A beam of light is passed through the sample to determine absorbance, transmittance, or fluorescence intensity, polarization and lifetime. Glass cuvets and cells are recommended for routine ultraviolet and visible region work, while quartz windows are available for transmissions from ultraviolet through far infrared. Quartz cells are noted for their durability compared to plastic or regular glass.