An LDR  and thermistor belong to the resistor family. A LDR (Light Dependent Resistor), is a variation of a resistor whose resistance is altered with varying levels of light. A Thermistor on the other hand is a type of resistor whose resistance changes with varying levels of temperature. 

What is an LDR (Light dependent resistor)

LDR stands for Light Dependent Resistor. This type of resistor has the ability to change its resistance as the ambient light levels change. The amount of current (electrons) that flows through the LDR is determined by its resistance, which is a function of light. 

Resistance of the LDR and light share an inversely proportional relationship. Low levels of light results in a high resistance. High levels of light cause the resistance of the LDR to drop allowing for more current to pass through it.  

LDRs are used in applications to detect light levels as their functionalities allow for it. They are commonly used in street lamps to detect when light levels have dropped during later parts of the day allowing the street lamps to know when to turn on.

What is a Thermistor

Thermistors are a type of resistor whose resistance varies with temperature. Its name is a combination of thermal and resistor. The amount of current flowing through a thermistor is determined by current which in this case is a function of temperature. 

There are different variations of the thermistor. However, the most commonly used thermistor’s resistance shares an inversely proportional relationship with temperature. At low temperatures, its resistance is very high allowing little current to flow through it. At high temperatures its resistance is low allowing for larger amounts of current to flow. 

Due to their unique ability, thermistors are often used as a cheaper alternative for a temperature sensor. They can be found in fire alarms which help detect potential fires. 

LDR and Thermistor circuit symbols

LDR vs Thermistor, which is the right option?

While the LDR and Thermistor are from the same family (resistor), they are different in how they operate. One’s resistance varies with light (LDR), and the other varies with temperature (Thermistor). But, which is the better option? One is not better than the other. Each has its own unique abilities that come in handy for a certain type of application. It all depends on the needs of the application.

Summary of an LDR and Thermistor

LDR (Light Dependent Resistor)Thermistor
Type of resistor whose resistance changes with varying light levelsType of resistor whose resistance changes with varying temperatures
Resistance and light share an inversely proportional relationshipResistance and temperature share and inversely proportional relationship
Used in applications where detecting light is essential, i.e. Street lamps, security alarms, etcUsed in applications where detecting temperature is necessary, i.e. Fire alarms, Heaters, etc

Applications of LDR and Thermistor

– Security Alarms
– Street lights
– Light intensity meters
– Smartphones
– Cameras
– Proximity switches
– Kitchen appliances
– Digital thermometers
– Circuit protectors
– Medical applications
– 3D printers
– Smoke/ Fire alarms