A light sensor is a photoelectric device that converts light energy (photons) detected to electrical energy (electrons). Seems simple? There is more to a light sensor than just its definition. It comes in different types and is used in various applications! Hence, in today’s light sensor guide, we’ll be exploring all you need to know about light sensors:
●What are the types of light sensors
●Light sensor applications
●List of light sensors available at Seeed
●How to use a light sensor with Arduino
What are the Types of Light Sensors?
Different types of light sensors are available, mainly Photoresistors, Photodiodes, and Phototransistors. Sounds technical? I’ll break it down with the explanations below!
1. Photoresistors
The most common light sensor type used in a light sensor circuit are photoresistors, also known as Light-Dependent Resistors (LDR). Photoresistors detect whether a light is on or off and compare the relative light levels throughout the day.
What are Photoresistors Made Of?
Photoresistors are made of highly-resistance semiconductor material called cadmium sulfide cell, which is highly sensitive to visible and near-infrared light.
How do Photoresistors Work?
As its name suggests, photoresistors work similarly to your regular resistors, but the resistance change depends on the amount of light it is exposed to. High light intensity will cause a lower resistance between the cadmium sulfide cell, while low light intensity results in a higher resistance between the cadmium sulfide cells.
This working principle can be seen in applications such as street lamps, wherein during the day, the high light intensity results in lower resistance, and thus they are not lit up when the sun is still shining brightly.
2. Photodiodes
Photodiodes are another type of light sensor. But instead of using the change in resistance like LDR, it’s more complex to light, easily changing light into a flow of electric currents. It is also commonly known as a photodetector or photo sensor.
What are Photodiodes Made Of?
Photodiodes are mainly made from silicon and germanium materials and comprise optical filters, built-in lenses, and surface areas.
How do Photodiodes Work?
Photodiodes work on the working principle called the inner photoelectric effect. When a beam of light hits, electrons are loosened, causing electron holes that result in the electrical current flowing through. The brighter the light, the stronger the electrical current will be.
Photodiode Light Sensor Applications
Since the current generated by photodiodes is directly proportional to light intensity, it makes it favorable for light sensing that requires fast light response changes. Also, they are very responsive to infrared light, thus more projects can be done in that field.
Here are some of the applications of photodiode:
●Compact disc players
●Smoke detectors
●Remote control devices
●Solar panels
●Medical applications
3. Phototransistors
The last light sensor type we’ll be exploring today is the phototransistor. The phototransistor light sensor can be described as a photodiode + amplifier. With the added amplification, light sensitivity is far better on the phototransistors. However, it does not fair better in low-light detection than in photodiodes.
Since both light sensor types share a similar working principle, do refer to the previous explanation!
Light Sensor Applications
Consumer Electronics
Ever wonder what’s behind your smartphone and tablets that allow for auto-screen brightness adjustments? Yes, it’s an ambient light sensor! It measures the ambient light level of your surroundings and determines the suitable brightness of your screen so that your eyes won’t hurt in the dark and you can read messages under the scorching sun!
Automobiles
Similar to how light sensor works on smartphones, it is used in automobiles to support the driver’s field of vision. The present light sensor detects surrounding ambient light, and if it’s getting too dark, it’ll automatically turn on the light systems. It is very helpful when you enter a tunnel or when it starts to rain!
Agricultural Usages
We all know crops need mainly two things for growth; sunlight and water. This is where a light sensor comes to play, helping farmers keep their crops hydrated yet not overhydrating them. Here’s how:
●A light sensor is connected to a sprinkler system, detecting the sunlight level and only activating it when the sun isn’t at its brightest
●It is used alongside other temperature sensors to help gather informative data for analytics purposes
Security Applications
Light sensors are connected to circuits and placed inside the cargo during shipments. They can detect whenever a container is accidentally opened, as there will be a change in light exposure. This helps to decrease lost goods and damages. Photoresistors are commonly used in this case.
Products and reference designs of Lighting sensor
Analog front end
Low-power high-precision amplifiers and comparators are needed to achieve long battery life. They are also important in the case of battery operated sensors and sensors that work based on harvested energy. The analog front end also needs high resolution ADCs. Analog front end includes Audio CODECs、Comparators、Precision op amps (Vos<1mV)、General-purpose op amps、Real-time clocks (RTCs) & timers, the Corresponding products are TAC5112、TLV3691、LPV811、TLV9041、TPL5111
Self-diagnostics/monitoring
Digital output temperature sensors, light sensors and humidity sensors are commonly used for self-diagnostics or monitoring. Sensor modules such as PIR, air quality, gas, microwave, noise and radar sensing are used. Self-diagnostics/monitoring includes Light sensors、Digital temperature sensors、Humidity sensors, the Corresponding products are OPT3001、TMP103、HDC3022
Isolated AC/DC power supply
An ultra low stand-by power consumption flyback power supply is used in applications where the sensor is powered from the mains. An external MOSFET may be needed in cases where high input AC voltage operation range is needed. Isolated AC/DC power supply includes Flyback controllers, the Corresponding product is UCC28700
Signal input/output protection
Sensor modules added to a master control unit need ESD protection on the interface connectors to ensure reliability. Signal input/output protection includes TVS diodes、ESD protection diodes, the Corresponding products are TSD05C、TPD1E10B06
Digital processing
Microcontrollers with built-in ADC and comparators are needed for digital processing. In the case of applications where signal processing is required, low power DSPs or ultra low power MCUs with dedicated hardware accelerators are needed. Digital processing includes MSP430 microcontrollers, the Corresponding product is MSP430FR6005
Wireless interface
Wireless MCUs with either 2.4GHz, Sub-1 GHz or Wi-Fi are used for wireless connectivity. Low power operation modes is an important consideration. Wireless interface includes Low-power 2.4-GHz products、Sub-1 GHz wireless MCUs, the Corresponding products are CC2640、CC2651R3、CC2630、CC1312R
Non-isolated DC/DC power supply
DC/DC converters and LDOs are needed to power subsytems such as the MCU, data converters and amplifiers. Low stand-by consumption and efficiency are important considerations. Non-isolated DC/DC power supply includes Buck converters (integrated switch)、Linear & low-dropout (LDO) regulators、Battery charger ICs, the Corresponding products are LMR51610、TPS629203、TLV773、TPS799、BQ25505
Power stage
MOSFETs and eFuses are used for power gating or for supplying power to various sections of the sensor. In some cases, in order to achieve the lowest power consumption, low power timers combined with load switches or MOSFETs or eFuses will be used. Power stage includes N-channel MOSFETs、eFuses & hot swap controllers, the Corresponding products are CSD17382F4、TPS1641
Summary
That’s all for today on light sensors. I hope with today’s blog, you get a deeper understanding of what it is, how it works, its usages, and what it takes to build one with an Arduino.
To help you easily get started, consider the list of touch sensors I’ve recommended, and hopefully, you will try out your very own light sensor projects today!
Previous： Electric power steering (EPS)
