Just like we have five senses to make sense of the world, electronic sensors help us in many ways in everyday life. They help detect changes in the physical environment. 

A light sensor helps detect changes in light. 

Having the ability to sense the change in light has many advantages and can be utilised a countless of different ways.

But where are light sensors used? Light sensors are used in many different industries and for a number of different applications. They can be found in consumer electronics like Mobile phones and Tablets, Streetlights, Automobiles, security systems just to name a few of their applications. 

What is the purpose of light sensors?

Thanks to advancements in technology we have a range of sensors available at our disposal. Depending on your needs there are sensors that can sense  temperature, speed, humidity, gas, angles etc.

The light sensor is one of the many sensors available.It is a device that has the ability to convert light (which are photons) into electrical energy (in the form of electrons). 

It’s main purpose is to detect changes in light level, and sees it used in many different applications where light intensity is a major component of the application.

I will cover the common applications where light sensors are used later in this article.

Different types of Light Sensors

With light sensors, you have three types available. They are the Photoresistor, Photodiode, and Phototransistor. 


A photoresistor light sensor is the most commonly used light sensor. It is used by hobbyists and makers due to its low price and availability. It is also known as a Light Dependent Resistor (LDR). The photoresistor varies its resistance depending on the intensity of light it detects.

The higher the light intensity of light, the lower the resistance, and vice versa. 


While the resistance of a photodiode light sensor varies depending on light levels, a Photodiode produces a varying electric current depending on the intensity of light. 

Brighter light levels cause a greeted current flow and vice versa. 


The final type of light sensor is the Phototransistor. The phototransistor has the same working principle as the Photodiode, but with the added benefit of an amplifier. 

Due to this amplifier, the phototransistor has better light sensitivity. The downside is that it doesn’t do too well in lower light applications. 

Can light sensors work by themselves?

No, light sensors only have the ability to detect changes in light and output this information in the form of a voltage or current. They cannot do any processing on the information they detect. 

Let’s take one of our five senses as an example. Our eyes let us sense the world around us visually. They have the ability to take in information. But, to make sense of that information we require a brain.

This is the same of light sensors. They require a brain, which can either be a Microcontroller or Microprocessor which are devices capable of taking the information that a light sensor outputs and processing it accordingly.

Applications of where light sensors are used?

You might not think that a light sensor has many uses, but it is a very versatile sensor that can be found in many applications. 

Below I have listed applications where light sensors are used. 

Application #1 where light sensors are used: Consumer Electronics 

The most common consumer electronic devices that use light sensors are Mobile Phones, and Tablets.

The light sensor is used in these devices to help with the auto-brightness function for the display. This is an essential function because the light sensor detects the light levels of the environment the user is using the device in and can adjust the brightness automatically. 

If the light sensor detects the environment to be dark, the brightness of the mobile phone and/or tablet does not have to be very high, so the brightness of the display can be reduced.

On the other hand, if the light sensor detects higher levels of light intensity, this will make it harder for the user to read the display and therefore the brightness of the device’s screen is increased. 

Application #2 where light sensors are used: Automobiles

You might have experienced driving in the night and noticed an oncoming car with their headlights off. Or, you might have been the driver who forgot to turn your headlights on.

Not turning your headlights on while driving at night can have devastating circumstances. You are essentially invisible to other drivers, and pedestrians.

Older models of cars did not have the ability to automatically turn on its own headlights if the driver forgot to do so. 

Newer cars are now capable of automatically turning on their headlights when ambient light levels drop (or you enter a tunnel) thanks to light sensors. 

Application #3 where light sensors are used: Streetlights

Headlights on cars help illuminate the road better, giving the driver better vision at night, and also giving other drivers and pedestrians better view of the car. 

But, there is only so much that a car headlight can illuminate the road. 

Another way of helping the drivers with night time driving is the use of Street Lights. They also help illuminate roads which help the driver see where they are going. 

Streetlights are also beneficial for people walking on footpaths. It lets people see where they are walking and helps them avoid any potential obstacles. Also, walking in the dark can be quite daunting. Having footpaths that are lit gives pedestrians a bit more reassurance.

Turning on streetlights manually every night is very inefficient. Also sun rises and sets at different times everyday.

Using light sensors allows them to turn on and off at the right time everyday. This also helps save electricity.

Application #4 where light sensors are used: Security

There are many forms of security systems to help keep you and your personal things safe. 

Lasers are often used in security because their beam is invisible to the naked eye. You can create a barrier of sorts when you use a laser in combination with a light sensor.

They are often used at the entry of stores and workplaces which lets owners know when someone has entered. 

Application #5 where light sensors are used: Horticulture

Plants and trees are essential to life. Without them we would not survive. They provide us with Oxygen that helps us breathe, as well as food to feed us. 

Growing plants, and trees is not a simple task. It requires a lot of care and thought like choosing the right soil to plant seeds, how much water to use and how much sunlight the plant receives. 

If a plant is left out in the burning sun without getting watered, the plant will get dehydrated and die. 

So how do light sensors help in the field of horticulture?

They are connected to sprinkler systems. The light sensor detects when the sun is at its brightest and activates the sprinkler system to ensure that plants and trees do not get dehydrated. 

They work in concert with other sensors to ensure that the right environment is created to allow plants and trees to thrive. 

Application #6 where light sensors are used: Safety

A fire can consume a house or workplace in a matter of minutes. No matter what time of the day, fires can be very dangerous.

But, they pose even more of a risk during the night when you are sleeping. A fire can start while you are asleep and you will not even be aware of it.

Smoke detectors were designed to alert you when a fire is present. There are many different types available, and one common type is the Photoelectric Smoke Detector. 

It uses light sensors to detect fires. The working principle is similar to that of the laser beam and light sensor mentioned above for the security system. An LED shines a beam of light inside the smoke detector toward the light sensor. When smoke disturbs the beam an alarm is sounded. 

Application #7 where light sensors are used: Medical 

Advancements of technology in the medical field have given us many life saving devices. 

Sensors play a big role in many of the medical instrumentation. 

Light sensors are used in devices such as the Pulse Oximetry (which helps measure the percentage of Hemoglobin) and Heart-Rate monitors (to measure heart rates). 

Application #8 where light sensors are used: Solar

Renewable energy is now becoming the new way of powering our world. It is more sustainable and better for the world. 

There are many different types of renewable energy and one abundant source is the Sun. 

Solar panels convert sunshine into electrical energy which then gets stored for later use. 

However, the sun does stay stationary in the sky. It moves across as the day goes by. In order to get the most energy from the sun, solar panels need to be positioned so they directly face the sun. 

But, they cannot do this on their own. Light sensors lend their helping hand by detecting where the sun rays are at their brightest and then position the solar panels accordingly to get the most out of the sun rays. 

Which type of light sensor are used in these applications?

I mentioned earlier the different types of light sensors, Photoresistor, Photodiode, and Phototransistor. I’ve covered some of the common applications where light sensors are used. 

Each type of light sensor has its advantages for different applications. 

Where are Photoresistor light sensors used?

Photoresistors are commonly used in applications where a slow response in light levels are sufficient such as turning on street lights, solar and horticulture applications.  

They are also great for lower light levels. 

Photoresistors are the go light sensor for hobbyists due to their ease of use, and low cost. 

Where are Photodiode and Phototransistor light sensors used?

When light levels change faster, and a quicker response is needed, Photodiode and Phototransistor light sensors are used. 

They are used for higher, more intense light levels.

Applications in the Medical Field, Smoke Detectors, Automobiles, Compact Disc Players etc use these kinds of light sensors. 

Where you wouldn’t use light sensors?

There are many different applications that require the help of some kind of sensor to detect a physical phenomenon like temperature, speed, gravity, etc.

Since there are so many sensors available, a light sensor wouldn’t be used for all of them. They would only be used where light is the main thing being measured. 

You wouldn’t use a light sensor to measure the temperature of a room. The need for a light sensor will present itself.

Final thoughts

Light sensors are a great and versatile tool that see them being used in many different applications across different industries such as Medical, Horticulture, Security, Safety and more. 

There are three types of light sensors used (Photo-resistor, Photo-diode, and Photo-transistor), each with their own advantages depending on the need of the application.