Bands and Colors of Tubes

 

Fluorescent tubes are available in several different colors. You have probably seen grow-lights for house plants which emit a much different color than the “white” tubes used in most houses and schools. Even among the white tubes variations exist. “Cool white,” for example, has more red than “Daylight” tubes. The variation in color is determined by the impurity states in the phosphor.

 

Use the Fluorescent Spectroscopy computer program to model the operation of a typical “cool white” fluorescent lamp. Click the Edit Properties button and set the input spectrum of the light to approximately 4.8 eV. The color pattern indicated on the scale represents UV light.

 

Use the mouse to drag the excited state band, which is illustrated on the energy diagram screen, to an appropriate energy.

 

Move the impurity state band to the appropriate energy so that the fluorescent lamp emits visible light (1.6 eV to 3.1 eV). Remember Cool White lamps have a lot of red. Assume that the resulting visible light will have an energy equal to the average energy for this range of values.

 

Describe the resulting energy band diagram with the respective energy values and each resulting transition.

 

How would the bands change for a “Daylight” (more blue) lamp?