Light emission – a Light-emitting diode is something that we are ?very familiar with, more commonly referred to as an ‘LED.’ LED’s are ?used in many applications and are becoming mo

1. Light emission – a Light-emitting diode is something that we are  very familiar with, more commonly referred to as an "LED." LED's are  used in many applications and are becoming more and more popular due to  their efficiency and longevity. "A typical LED for lighting can deliver  50–60 lumens per watt, which is approximately five times greater  efficiency than a standard incandescent bulb (Thomas L Floyd)." When the  LED is in forward bias, electrons that combine with holes in p-type  materials coming from the n-type materials. Once recombination takes  place an energy is released in the form of photons. A semiconductive  material is what allows the photons to be projected as visible light.

2. A phototransistor is similar to a Bipolar Junction Transistor  (BJT) except the base currents are generated from two different sources.  The base current in a BJT is produced by a voltage source while the  phototransistors come from a light source. Phototransistors can be found  in punch card readers, counting systems, and even in light  controlling/detection systems. The phototransistor operates dependent on  the level of radiation detected in form of light, and not just any  light source but only those within a certain range of wavelengths. 

References:

Floyd, T. L. (2017). Electronic Devices (Conventional Current Version) (10th ed.). Pearson Education (US). https://ecpi.vitalsource.com/books/9780134414553 

 Links to an external site.

 Roshni Y (2023) What is a Phototransistor? Definition, Construction, Working, Characteristics Curve of Phototransistor – Electronics Desk