Ambient light sensor

How Ambient Light Sensor Helps Everybody??

Is there anyone of you who don’t have a smartphone or TV or a smartwatch etc? Very few, right?? Have anyone of you heard the word ambient light sensor? Come on, think think. When buying a brand new phone or a luxurious and comfortable smartwatch you might have seen on the specs page.

Today’s topic is about that only – Ambient Light Sensor. 




We use it but don’t appreciate how that minute thing benefits us. So, stay till the end to know proper info about ALS.

Shall we begin ?? [Ohh, Yes]

A]. What Ambient Light Sensor Means
B]. Types Of Ambient Light Sensor
C]. Wearable Devices that incorporate An Ambient Light Sensor
D]. How Does ALS Works?

Before explaining what is an ambient light sensor, we must first understand what is ambient light.

The ambient light sensor comes from ambient light or available light. Available light relates to the source of light that is already accessible to us naturally i.e – sunlight, moonlight, artificial [room] lights etc.

There are 2 varieties of light –

1]. Outdoor Lights
2]. Indoor Lights

1]. Outdoor Lights




Outdoor Lights includes –

a]. Fireworks

b]. Pollution [Light]

c]. Flashlight from a torch or from your smartphone

d]. Street Lights

e]. Stars, which are dim light

f]. Moon/Sun Light

2]. Indoor Lights


chandelier lights


Indoor Lights includes –

a]. Light Bulbs

b]. Candles

c]. Chandeliers Lights

d]. Fluorescent Lamps

What is Ambient Light Sensor

Ambient light sensor [ALS] is an element in your smart devices you practice like – smartwatches, notebooks, smartphones, TV’s etc. What follows is – it has a photodetector which is utilised to feel the volume of ambient light present and relatively dim the device display to match it.

Because of that, it avoids the display to be too bright when your eye pupils are suitable for proper vision in a dark room or on the contrary, too dim when used outdoors in the fresh sunny day.

It also benefits and elongates the battery lifeline. Now, what is this term “photodetectors”

Photodetectors are also coined as photosensors are light sensors. The photodetector has a [p-n junction] which turns light photons into a current.

Phototransistors and Photodiodes are a few instances of photodetectors.

Types Of ALS

There are usually 3 types of ambient light sensors –

1]. Photodiodes
2]. Photonic integrated circuits
3]. Phototransistors


  • Semi-conductor device that converts light into an electrical current. It happens when the current is generated when photons are absorbed in the photodiode

Photonic Integrated Circuits [PIC]

  • An integrated optical circuit is a device that can blend several more than 2 photonic functions and is related to an electronic integrated circuit.


  • A light-sensitive transistor. The general type of phototransistor is recognised as the photobipolar transistor. Was developed by Dr John N Shive at Bell Labs in the year 1948.

Wearable’s That Incorporate An Ambient Light Sensor

Following wearable’s contain ALS –

A]. Basis B1
B]. Withings Activite
C]. Atlas Fitness Tracker
D]. Samsung Gear S
E]. Sony Smartwatch 3 SWR50
F]. Samsung Gear S3
G]. Microsoft Band
H]. Withings Activite Pop
I]. Fitbit Blaze
J]. Moto 360
K]. Zgpax S5
L]. Microsoft Band 2
M]. Fitbit Surge
N]. Samsung Gear S2

Ambient Light Sensor – How it Works? 

Light Sensors are tested by illuminance.

There are 2 kinds to measure illuminance –

  • 1]. Photoresistor
  • 2]. Photodiode

1]. Photoresistor 

A light-dependent resistor which means that if there’s any difference in the illumination of the light shined on that object. Because of the aforementioned, the shift will happen in resistance.

Photoresistors are not expensive than photodiodes. Also, are not that excellent in precision. This eventually is used to analyse the relative light levels or to examine whether the light is turned on or off.

2]. Photodiode

Generally, Light sensors sometimes utilise a piece termed as a photodiode so that it can measure the illuminance.

How This Occurs ??

What happens is, when light rays hit a photodiode this makes the electrons vulnerable which in turn points to an electric current to pass.

The brighter the light – stronger the electric current

The dull the light – weaker the electric current

After this, the current can be calibrated to reflect the illuminance of the light. {e.g – Solar panels are huge photodiode light sensors}

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