How to differentiate between a black led and a phototransistor?
Answers
LDR is short form of light dependent resistor…as the name suggests it is a resistor that is sensitive to light.. That is the resistance of it changes with falling light…the resistance is inversely proportional to light intensity, in general…a small 0.5cm LDR, that is used in most projects have a resistance greater than 20Megohm in complete darkness and resistance falls to 200ohms or even less in strong light…. They are made of light sensitive semiconductor material
Photodiode is a pn junction diode, specially made for light detection…the diode is usually kept in reverse bias condition…as light falls on the depletion region, electron hole pairs are generated and that creates a photocurrent, it increases with increasing light…. The reverse bias is applied so that the depletion width region is exposed to light and photocurrent is generated…so this is also used in light detection purposes, it is also used to detect IR lights