Light Sensor Secrets Revealed: Uncovering the Science Behind Measuring Light!

Light Sensor Secrets Revealed: Uncovering the Science Behind Measuring Light!

Hands down, light sensors are a treasure trove. Looking into how these scientific wonders work allows us to deploy them with higher operational efficiency. In the process, you become effective enough to expand your world like never before.


The truth of the matter is we don’t just need light. Rather, we need ample light.


Too much heat from the sun can scorch our skin, and if unchecked may even cause skin cancer. And yet, too little sun in our lives can also lead to health complications. Having the right amount of light is, therefore, paramount.


This is where light sensors come in handy. They save us the trouble of guessing by determining how intense light is within our surroundings.


In this post, we’ll walk you through how all that happens and how such a wonderful instrument as a light sensor has helped countless people before you—with great benefit. Read on. 



How Light Sensors Work


By definition, a light sensor is a photoelectric instrument that gauges the amount of light (or light intensity) in a given area. Essentially, the device does this by converting light energy (photons) into electrical energy.


The Science Behind Light Sensors


At its very core, light sensors rely on the photoelectric effect. It’s simple really.

The photoelectric effect states that electromagnetic radiation (such as light) can cause electrons in a metal to get excited when bombarded

As electrons in the metal get excited, electrical activity is produced. The stronger the amount of incident light, the greater the electrical output. 

Image 1: Electrons in a metal plate getting excited when hit by light energy


Now, to be able to measure light intensity, we must be able to quantify light energy. And today, there are three ways to do just that: 

Unit of Measurement Definition Symbol


Luminous intensity equivalent to one candle. cd


The total amount of light that falls on a surface of 1 square meter. lx


The total amount of light emitted in all directions by a light source. (e.g., lamp) lm


Table 1: Ways to Measure Light Intensity

For instance, a flashlight that could generate 1 cd (candela) of light intensity may have 12.5 lm (lumen) of luminous intensity in all directions. But if you cover half of its lamp, said flashlight will still maintain a 1 cd light intensity but will have only 6.25 lm—half of its original luminous intensity. 


On the other hand,  the amount of light said flashlight generates on a table nearby can be measured in lux. Another term for this is illuminance


Light Sensor Types


Basically, there are two main light sensor types. Though both react to the presence of light, one uses the amount of electric current produced while the other relies on electrical resistance to measure illuminance. 


1. Photodiode

Image 2: Photodiode electronic symbol. 
Photodiodes are semiconductor diodes that are sensitive to photons of light. As the amount of electrical output photodiodes produced is directly proportional to the intensity of the incident light, we can measure the illuminance of a particular light source. 
A glorious example of light-induced electric charge is solar panels. Essentially, solar panels that power homes and buildings are large photodiodes in action.

2. Photoresistor

Image 3: Photoresistor electronic symbol. 
Photoresistors, also known as LDRs (light-dependent resistors), are light-sensitive semiconductors that decrease in resistance with increasing light. The stronger the light source, the smaller the electrical resistance becomes. 
While photoresistors are cheaper than photodiodes, they’re less accurate. They are utilized most in light-activated and dark-activated circuits such as lamps that are switched on/off depending on the surrounding light. 


Another common light sensor type is the phototransistor. However, it’s essentially a photodiode on steroids—armed with greater capabilities. Although it’s much more complex in design, phototransistors operate much like photodiodes. 



Most Common Applications of Light Sensors


Our ability to measure the intensity of light allows us to deploy just the right amount of light. In this regard, light sensors play a huge role in expanding our world by showing us illuminance. Below are some of the most common ones:





There may not be work that’s more reliant on proper lighting than photography. With light meters, photographers can determine incident light on a subject or reflective light on a background. Doing so allows them to adjust lighting accordingly, not to mention choose the most spot-on shutter speed and f/stop.


Engineering & Construction 

Engineering & Construction


Engineers and architects can make the most of light meters to determine the best window or lighting placement. On your end, you can use the device to choose the best lighting fixture for home improvement.


Consumer Electronics

Consumer Electronics


Light sensors are central to how smart devices operate. You may be wondering how your smartphone detects motion.  And the answer lies in these devices using light sensors such as phototransistors, measuring the presence of light or lack of it to adjust accordingly. 


For Security Purposes

Security Purposes


It’s surprising but light sensors are central to the function of a smoke detector. Placed at a certain angle inside the smoke detector chambers, a light sensor detects when the light from an LED is disrupted (presence of smoke). This way, these amazing devices are your first line of defense. 


Public Spaces

Public Spaces


With inadequate lighting in a public space (e.g., parks, streets, highways), you invite disaster. A car park that’s dimly lit will encourage criminals to operate endangering people’s lives and properties in the process. 

  • A University of Sheffield report showed that when areas are well-lit, crime reduction increases to 36%, and rape crimes lower by 38%.

Light sensors can play their part by ensuring adequate lighting for everyone’s safety.


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