Ambient Light Sensor Working and Applications

The ‘lux’ is the standard international unit of the ambient light used for the illuminance. The typical performance of this sensor ranges from below 50 lux to over 10,000 lux. Here 50 lux can be generated inside dim light whereas over 10,000 lux at noontime. The lux is the SI unit for illuminance and that is equivalent to one lumen for each square meter. This is used in photometry for measuring the intensity which is perceived through the human eye when light hits through a surface. In the year 2004, there are the phones are many phones are designed with ambient light sensor and 30% of the phones are sold out. Whereas in the year 2016, 85% of the phones are inbuilt and sold out.

What is an Ambient Light Sensor?

An ambient light sensor is one kind of component which is utilized in mobile devices, smartphones, notebooks, LCD TVs, and automotive displays. Ambient light sensor working principle is, it is a photodetector, used for detecting the sum of ambient light nearby & appropriately reduces the mobile screen’s light.

So this avoids the screen brightness whenever the users are modified for vision within a dark room otherwise less brightness as the mobile is utilized outdoors during the daytime. By dimming the mobile screen one can prolong the lifetime of the battery.


There are three types of ambient light sensors which are namely photodiodes, photonic ICs, & phototransistors which combine a photodetector & an amplifier in one device.

Ambient Light Sensor Circuit

The ambient light sensor is considered like harvesting energy source to control bathroom fixtures, remote weather sensors, heartbeat monitors & low power devices. The ambient light can be measured accurately using the harvesting system at the heart of energy. The design of a harvesting system illustrates an easy, commercial circuit which offers a voltage that is proportional to the strength of ambient light.

The sensor used in the circuit is an LDR (light-dependent resistor), and the resistance of this will change with ambient light strength. When the sensor is in darkness, then the resistance will be decreased from millions of ohms in darkness as well as few hundreds of ohms in clear light.


It is capable of detecting small or large fluctuations within light levels, it can differentiate among one light bulbs, straight sunlight, entire darkness, etc. Every application needs a suitable circuit as well as a physical arrangement for the correct lighting scenario. The sensor which is used in this circuit can be connected in a clear and waterproof field.

The above ambient light sensor circuit gives an o/p voltage that reacts to both the light intensity & the input voltage with the LDR which is working as the gain resistor to the instrumentation amplifier (AD8226). The transfer function of the instrumentation amplifier is given below.


In the above equation, ‘G’ is the gain of the circuit, and ‘VIN+ as well as VIN-the positive & negative input voltages, and ‘VREF’ is the voltage at the reference pin. When the VIN- (negative input) and reference pin are connected to ground and VIN+ (input pin) is applied toward the positive input, then the gain will be

G = VOUT/ VIN+ = 1 + 49.4 kΩ /LDR

LDR = (49.4 kΩ) / (VOUT/ VIN+) – 1

Whenever the LDR value is known, then the value can be decoded into the light level. Therefore, the task turns into one of observing op-amp’s output with an input voltage.

Here the positive voltage can be an AC voltage, or a DC voltage, or a balanced version of the power supply. So, the gain exactness can depend on the precision of two inside thin-film resistors which are trimmed.

The above circuit is used to calculate ambient light by changing the photo resistor’s resistance to a voltage and it can be calculated at a distant place. The instrumentation amplifier was selected due to its broad operating range of power supply which ranges from 2.7 V to 36 V, rail-to-rail o/p, functional completeness, and low quiescent current.

This circuit handles with a gain resistor which ranges from a few ohms to infinity. Because these amplifiers turn into less-expensive and its improved act makes them perfect replacements intended for op-amps (operational amplifiers).


The applications of the ambient light sensor include the following.

The ambient light sensor is used to control the backlight of an LCD display based applications to control display brightness of mobile for reducing battery life. The applications of this sensor range from consumer electronics to automotive. This is the main benefit of mobile applications.

These sensors are also used in all types of light sources like natural sunlight, incandescent lamps, and fluorescent. For instance, AMIS74980x ambient light sensor from AMI Semiconductor’s is used within both automotive as well as consumer applications. The main feature of this sensor is, allowing the display controller to regulate the intensity in less dark current.

Likewise, the ambient light sensor like ALS-SFH5711 from OSRAM hypes human eye characteristics intended for mobile & automotive applications. These devices are used to replicate the sensitivity arc of the person’s eye, allowing mobile displays and the levels of its brightness to be attuned more accurately. These sensors are used in automotive applications like headlight control & cockpit dimming.

The APDS-9004 ambient light sensor from Avago Technologies is used for backlighting control in DVD players, consumer LCD displays, mobile phones, notebook PCs, digital cameras, etc. The main feature of this sensor is an automatic alteration to save power & to increase the LCD screens life in handy display devices. Additionally, these sensors control the backlighting based on the program set by the maker.

This sensor is also be used in indoor as well as outdoor lightings for turning on/off which include street lighting, electronic signals as well as signs.

Thus, this is all about an overview of an ambient light sensor. From the above information, finally, we can conclude that this sensor decides how much light can be accessible within the region surrounding the phones. It automatically regulates the intensity of the mobile screen in order to preserve the life of mobile battery & to adjust the mobile screen to relieve eye tension. Here is a question for you, what are the benefits of a light ambient sensor?