Light sensors seem pretty simple. They sensethe light, just like a thermometer senses the temperature, and a speedometer senses speed. Temperature and speed are easy to comprehend because we sense them in a straight-forward way. But light is very complicated. Temperature and speed are intensive properties, so they don’t depend on the mass or size of an object. Light can be measured as an extensive property, meaning the total light collected depends on the size of the collector (e.g. a landfill solar array collects more light than a tiny solar phone charger), or intensively by dividing by the area. But what are light sensors even measuring? Photons? Energy? It’s complicated. The units are important to understand before attempting to understand light sensors. Before we can properly understand light sensors and how to apply them, we need to be able to quantify light. Unfortunately, measurement of light uses some strange units. For example, lightbulbs are usually rated using lumens, but light sensors typically take measurements in lux. On top of that, both lumens and lux are based on an arcane base unit called the candela. This unit is used to describe luminous intensity, which is how strong light appears to a human eye. It is based on an SI-official formula that weights every wavelength of light in a beam based on how sensitive the human eye is to it. The higher the luminous intensity of a beam of light, the more sensitive the human eye is to it. (Candelas were formerly known as “candles”, and the luminous intensity of a normal candle is approximately one candela. Clever, right?) The reason candelas are not used to compare lightbulbs and flashlights is that the intensity of a beam depends not just on the output of the bulb, but also how much of that output is concentrated in a particular direction. Most flashlights use mirrors behind the bulb to concentrate more light in the output direction and therefore appear brighter. This means that the bulb has increased intensity in a direction, while using the same amount of power and emitting the same total amount of light. To properly measure the output of a bulb, we need a new unit: the lumen.
Light Sensor Units
The Candela
Lumen
The lumen is used to measure the total luminous flux of a light bulb. This is the product of the luminous intensity (in candelas) and the solid angle that the beam fills (in steradians). A bulb emitting light in all directions might have a luminous intensity of 10 candelas, which when multiplied by the full 4π steradians would have a luminous flux of 126 lumens. Like inside a flashlight, a mirror on one side of the bulb would make the other side appear brighter due to the reflection of half of the bulb’s output. The intensity of the light would double to 20 candelas, but the solid angle would halve to 2π steradians. Multiplying the intensity of the light opposite the mirror and the new solid angle would still give 126 lumens of luminous flux. No matter how the light is reflected and concentrated, this bulb will always produce 126 lumens of luminous flux.
Lux
If light bulbs are rated using lumens, why do light sensors have to use a different unit? It’s the reason musicians aren’t blinded at concerts. A single flashlight might seem blinding when shined an inch away from Drake’s eyes, but a sea of phone flashlights pointed at the stage isn’t bright at all. Because the light scatters as it leaves the phone, only a small amount of light hits his eyes on stage. As an object moves away from a light source, the share of the light that it receives also decreases. To properly measure the luminous flux as perceived by a surface, called illuminance, we use a unit called lux, which is equal to one lumen per square meter. At the same distance from a light source, a 1 square meter sheet is subjected to the same illuminance as a 10 square meter sheet. The larger sheet collects ten times as much light, if measuring luminous flux in lumens, but its area is just as large, so the illuminance is the same. If the sheets move toward the light source, the solid angle occupied by each the sheet increases, and therefore the illuminance also increases. The intensity of the light is constant, and the area of the sheets is constant, but the solid angle occupied increases, therefore increasing the illuminance they receive. Light sensors have to measure illuminance because it represents the light cast on a unit area, and because they cannot know what solid angle they occupy.
Uses for Light Sensors
Placement Detection
Light sensors measure illuminance, which can be used to measure more than the brightness of a light source. Because the illuminance decreases as the sensor moves away from a steady light, the light sensor can be used to gauge relative distance from the source.
Figure 1: Graph shows Illuminance vs Distance
Light sensors are almost always a flat, one-sided surface, so the solid angle occupied by the sensor as viewed from the light source can change depending on its orientation. With the light sensor perpendicular to the direction of the light, it is occupying the largest solid angle possible. As the light sensor rotates away from the light, its solid angle decreases, with the illuminance therefore also decreasing, until the light sensor ultimately detects no direct illuminance when parallel to the light beams or when facing away. This fact can be used to determine the angle of incidence of a light beam on the sensor.
Figure 2: Graph shows Illuminance vs Angle
Brightness Control
Light sensors have a lot of uses. The most common use in our daily lives is in cell phones and tablets. Most portable personal electronics now have ambient light sensors used to adjust brightness. If the device can sense that it is in a dark place, it turns down the screen brightness to save power and not surprise the user with a very bright screen.
Another commonplace use for light sensors is controlling automatic lights in automobiles and streetlamps. Using a light sensor to trigger a bulb when it is dark outside saves the slight hassle of turning on the lights and saves power in the day when the sun is bright enough.
Security
There are many more uses than consumer convenience, however. Detecting intrusion into containers or rooms is an important security application. When shipping expensive cargo, it can be important to know when a shipping container has been opened, so that cases involving loss of product can be solved easier. A cheap photo-resistor could be used to log each time the container is opened, so it can be determined at what point in the process thieves raided the container, or if the sender was being dishonest and claimed the container must have been robbed.
While light sensors are the only products that can give meaningful data regarding light, many other goods are sensitive to light. For example, paintings and photographs on paper and older works of art can be damaged due to exposure to sunlight, so it is important to know how much light they are exposed to. When shipping a work of art, a light sensor could be used to verify that it was not left in the sun for too long.
Planning
A light sensor could also be used for siting the art to a permanent location. Areas near the entrance or windows of a museum could have sunlight too harsh for particular materials, so a light sensor could be used to locate art appropriately. This is similar to the method for siting solar arrays on homes or in fields. It makes no sense to build and install a solar panel in a certain spot if it won’t receive much direct sunlight, so a light sensor is used to find the best placement with the strongest direct sunlight. (As I mentioned, a solar panel is just a very large light sensor, but it’s easier to use a handheld device to test the sunlight than use the panel itself.)
Agriculture
Sunlight has important implications on agriculture, especially in the water-deprived American West. Different crops need different amounts of sunlight, so it is important to know which plots of land get the most exposure. As water supply becomes more strained in places like Utah, farmers have a financial and social obligation to limit water consumption, while also keeping their crops hydrated. One tactic being adopted is to water crops in the afternoon or evening, to avoid the hot sun cooking off the water before the soil and plants can properly absorb it. A light sensor could be used to manage a sprinkler system automatically, only watering when the sun is not at its brightest. When coupled with other weather-monitoring equipment to gather data regarding temperature, pressure, and humidity, a system could not only water when the sun is dim, but also intelligently detect oncoming rain or clouds to optimize its watering schedule.
How light sensors work
Now that you understand the mess of units that quantify light, we can start to understand how illuminance is determined using light sensors.
Photodiode
Light sensors sometimes use a component called aphotodiodeto measure illuminance. When beams of light strike a photodiode, they have a tendency to knock electrons loose, causing an electric current to flow. The brighter the light, the stronger the electric current. The current can then be measured to return the illuminance of the light. If light-induced electric current sounds familiar, it is because this is the operating principle of the solar panels used to power road signs and homes. Solar panels are basically very big photodiode light sensors.
Photo-resistor
Another type of light sensor is thephoto-resistor.A photo-resistor is light-dependent resistor, meaning that if there is a change in the brightness of the light shined on it, there will be a change in resistance. Photo-resistors are cheaper than photo-diodes, but are much less accurate, so they are mostly used to compare relative light levels or simply whether a light is on or off.
Available light sensors
As mentioned earlier, light sensors (photo-resistors and photo-diodes) are versatile and not super expensive, so there are a lot of options out there, from basic components to highly-accurate data loggers.
One method for collecting illuminance data is using the usual small computing platforms like Arduino or Raspberry Pi. Using these platforms to measure illuminance is useful because programming and interfacing with a computer is simple and the photo-resistors are very affordable. In addition, it is possible to use the light sensor in tandem with other data collection hardware. However, a system like this would not be very accurate or user-friendly.
Amazon has a lot of consumer light meters that are typically used for photography. They’re all compact and easy to use, with data appearing on-screen in real time, and all have a reasonably good refresh rate of a few hertz. These would likely be best used for comparing relative brightness between rooms indoors, but most have a wide range, so outdoor use is also an option.
As a matter of fact, we actually sell a light sensor as part of our enDAQ sensors. It uses an Si1133 photodiode, and logs illuminance data on the device along with acceleration, temperature, pressure data. Because illuminance has the candela as a base unit, measurements of light need to be adjusted to account for non-visible electromagnetic radiation. The Si1133 does this by measuring the infrared light separately and using it to properly adjust the illuminance data. The enDAQ sensor’s light sensor also measures the UV index in addition to visible light.
Light sensors are some very versatile, affordable components with a lot of potential applications. How are you planning to use light sensors? I would love to hear your ideas in the comments.
For more on this topic, visit our dedicated Environmental Sensors resource page. There you’ll find more blog posts, case studies, webinars, software, and products focused on your environmental testing and analysis needs.
FAQs
What is light sensor and how it works? ›
Light sensors detect light and convert light energy to an electrical signal output. Once converted into electrical energy, the radiant energy within the infrared to ultraviolet light frequency spectrum source can then be measured.
How are light sensors used? ›Light sensors measure illuminance, which can be used to measure more than the brightness of a light source. Because the illuminance decreases as the sensor moves away from a steady light, the light sensor can be used to gauge relative distance from the source.
What is the unit of light sensor? ›The standard international unit for the illuminance of ambient light is the lux. The typical performance of an ambient light sensor is from less than 50 lux in dim light to over 10,000 lux at noon.
How do light sensors work simple? ›The light sensor is a passive device that converts the light energy into an electrical signal output. Light sensors are more commonly known as Photoelectric Devices or Photo Sensors because they convert light energy (photons) into electronic signal (electrons).
Why do we need light sensors? ›This system ensures areas are not too bright or too dark. As daylight levels change, the sensors automatically adjust the lights. Another type of light sensor is the 'occupant sensor' which turns on/off or adjusts lighting levels by detecting human presence.
Where are light sensors applied? ›Light sensors are used in offices to control brightness levels, which is similar to how your mobile phone brightness works in response to the sun and external light levels. Light sensors are also used in agricultural settings to assess how much light the soil is absorbing, which enables plants to grow.
Where are light sensors found? ›You can usually find where the windshield sensor is located either: Mounted on the windshield next to the rain sensor. Behind the rearview mirror. On the dash near the windshield edge.
How do you make a light sensor? ›How To Make Light Sensor - DIY Automatic Street Light - YouTube
How light sensor works in mobile? ›Mobile Sensors | Ambient Light Sensor - YouTube
How do lightbulb sensors work? ›Motion-activated light bulbs are paired with infrared light sensors. These bulbs automatically turn on when motion is detected in darkness or over any predetermined period of time. These lights turn off after the movement has subsided without the need for a controlling switch.
Is a light sensor input or output? ›
A light sensor is an input device that measures light levels.
How does a sensor work? ›Put simply, a sensor converts stimuli such as heat, light, sound and motion into electrical signals. These signals are passed through an interface that converts them into a binary code and passes this on to a computer to be processed.
How do night light sensors work? ›Some nightlights include a photocell, which enables them to switch off when the ambient light is sufficiently bright. Other designs also feature a built-in passive infrared sensor to detect motion, and only switch on when somebody is passing by in the dark.
What is a light sensor circuit? ›What is a Light Sensor Circuit? The light sensor circuit is a simple electrical circuit, which can be used to control the (switch on and off) electrical load appliances like lights, fans, coolers, air conditioners, street lights, etc., automatically.
How do you test a light sensor? ›Light Sensor Test (trouble shooting) - YouTube
Who invented light sensor? ›Achievements and awards. Eric R. Fossum has published over 300 technical papers, and holds more than 170 U.S. patents.
What is light sensor switch? ›This light sensor switch circuit allows the automatic connection of a lamp when the light is low (at nightfall) and will maintain the lamp ON for a certain period of time.
Do light sensors have cameras? ›There are no cameras involved at any point. Instead, motion sensors rely on different kinds of radiation (which sounds scary, but it's perfectly safe and normal). Most motion sensor lights use a PIR sensor – a passive infrared sensor. It's passive, so it doesn't emit anything.
Which sensor is used to detect the amount of day light available? ›Phototransistors, photoresistors, and photodiodes are some of the more common type of light intensity sensors. Photoelectric sensors use a beam of light to detect the presence or absence of an object. It emits a light beam (visible or infrared) from its light-emitting element.
How do you wire a light sensor? ›Connect the black, white, and red wires from the light sensor to the wall wires. Twist the hot black wires together and screw a plastic wire nut onto the ends. Repeat this for the neutral white wires and red load wires. The live and neutral wires are always black and white, respectively.
Which sensor is used for motion detection? ›
There are two widely used types of motion sensors: active ultrasonic and passive infrared (PIR). Active ultrasonic sensors and passive infrared sensors are the two most common motion sensor technologies, both of which are known for their accuracy and reliability.
How does a color sensor works? ›A color sensor is a type of "photoelectric sensor" which emits light from a transmitter, and then detects the light reflected back from the detection object with a receiver.
How do I use a light sensor Arduino? ›Place the LDR on the breadboard and attach the 10k ohm resistor to one of the legs of LDR. Connect the A0 pin of arduino to the same column of resistor and LDR. This is to fetch the intensity of light from LDR to the arduino through A0 pin. Connect the other end of resistor to the negative rail of breadboard.
What is light sensor and its types? ›Common types of light sensors are photodiodes, photoresistors, phototransistors, and photovoltaic light sensors. These components can be used in applications such as light sensing in mobile devices, automatic outdoor lighting, proximity sensors, and renewable energy.
Do phones have light sensors? ›Smartphones contain many built-in electronic sensors that can measure phenomena such as sound, light, motion and more. In this activity you'll use the light sensor on a phone or a tablet to examine the brightness of light from different light sources and locations.
Is a light sensor analog or digital? ›Some common examples of analog sensors are light sensors (LDRs), sound sensors, pressure sensors, and analog temperature sensors. Similarly, there are some commonly used digital sensors such as digital temperature sensors and digital pressure sensors.
Which sensor is used to detect darkness? ›LDR (Light Dependent Resistor): LDR or Light Dependent Resistor is one of the commonly used light sensors. In this project, we are using an LDR to detect darkness i.e. when the intensity of light decreases.
What is dark light sensor? ›Introduction. A circuit that detects darkness or the absence of light is known as a darkness detector or dark detector. We can create different night light sensor Dark Detector electronics projects by employing the most basic components like LDR, 555 timer IC, etc.
How do you make a sensor circuit? ›...
How to Build the Touch Sensor Circuit
- Step 1: Connect The Transistor. Start by connecting the transistor a little bit down on the board. ...
- Step 2: Connect The Resistor. Next, connect the resistor. ...
- Step 3: Place The LED And Touchpad. ...
- Step 4: Connect The Touchpad. ...
- Step 5: Touch It!
Accelerometer. An accelerometer sensor reports the acceleration of the device along the three sensor axes. The measured acceleration includes both the physical acceleration (change of velocity) and the gravity.
How many sensors are in a phone? ›
The Android smartphone provides two sensors that let you determine position of device- geomagnetic field sensor with combination of accelerometer sensor.
Which sensor is used in today's mobile phone screen *? ›3. Which sensor is used in mobile phones? Explanation: Capacitive touch sensors are widely used in most of the portable devices like mobile phones and MP3 players.
Do light sensors work with LED lights? ›The answer is yes. LED lights can work with motion sensors with the right configurations. A lot of lighting technologies today make use of motion sensors attached to LEDs. These luminaries monitor movement in a given area, lighting up when movement is detected.
How does a motion sensor light switch work? ›The sensor uses a photodetector, which converts light in the wavelengths into an electrical current. A detectable difference triggers the minicomputer housed in the detector to activate the switch. To prevent nuisance switching, the computer ignores slow changes in room temperature due to sunlight.
How does a motion sensor work? ›A motion sensor uses one or multiple technologies to detect movement in an area. When a sensor detects motion, it sends a signal to your security system's control panel, which connects to your monitoring center. This alerts you and the monitoring center to a potential threat in your home.
Do sensors need electricity? ›In most cases, sensors and more specifically analogue sensors generally require an external power supply and some form of additional amplification or filtering of the signal in order to produce a suitable electrical signal which is capable of being measured or used.
What type of device is a sensor? ›What is a sensor? A sensor is a device that detects and responds to some type of input from the physical environment. The input can be light, heat, motion, moisture, pressure or any number of other environmental phenomena.
What is sensor in simple words? ›1 : a device that responds to a physical stimulus (such as heat, light, sound, pressure, magnetism, or a particular motion) and transmits a resulting impulse (as for measurement or operating a control) 2 : sense organ.
Where are sensors used in daily life? ›Some household appliance applications using sensors are the boiler, washing machines and dishwashers for heating systems, and other white products. Many vehicles, including automobiles, trains, buses, etc., employ sensors to monitor petroleum temperature and pressure, jets and steering systems, and so many more.
How many sensors are there? ›There are two types of sensors: Direct Sensor: A sensor that can convert a non-electrical stimulus into an electrical signal with intermediate stages. Eg: thermocouple (temperature to voltage). Indirect Sensor: A sensor that multiple conversion steps to transform the measured signal into an electrical signal.
Why do we use light at night? ›
Light at night allows our primary sense, vision, to operate well. This has benefits for both the individual and for society. These benefits are related to some very basic human motivations. Recognizing these benefits is necessary to limit the use of light at night.
What is the purpose of night light? ›To help you get to sleep, turn on the night light and your display will show warmer colors at night that are easier on your eyes.
What is a day night sensor? ›The DNS25 Day/Night Sensor can automatically turn on or off lights at dusk and dawn. It is not only convenient but also practical; it can control the lighting loads by working only at night. Examples of use are street lights, office lights, warehouse and factory lights, garden lights, etc. SPECIFICATION.
What does lux mean on light sensor? ›LUX: Lux is what controls the day and night setting it will have a picture of a sun and a moon, moving it more towards the sun will have it come on when it is lighter or moving it towards the moon will have it activate only when it is dark.
What is the relationship of light sensor and LEDS? ›Introduction: LED AS a LIGHT SENSOR
Which is intentionally made to emit the light and it uses semiconductor material. so this can be used as a light sensor. IF YOU WILL MEASURE VOLTAGE OF LED IN LIGHT AND IN ABSENCE OF LIGHT YOU WILL GET FAR DIFFERENCE BUT IT IS DIRECTLY PROPORTIONAL TO LIGHT INTENSITY.
What is a Sensor Circuit? Firstly, a sensor is an electronic device that delivers output from sensing changes in events or quantities. So, sensor devices that convert various inputs into electrical or optical work are sensor circuits. By default, sensors measure changes in their environment.
How do lightbulb sensors work? ›Motion-activated light bulbs are paired with infrared light sensors. These bulbs automatically turn on when motion is detected in darkness or over any predetermined period of time. These lights turn off after the movement has subsided without the need for a controlling switch.
What is light sensor in IoT? ›Optical Light sensors
These sensors convert rays of light into electronic signals by measuring the quantity of light and then turning it into a form that can be read by an instrument, in our case the IoT system. Light sensors have a multitude of IoT applications, from office management to agriculture.
Some nightlights include a photocell, which enables them to switch off when the ambient light is sufficiently bright. Other designs also feature a built-in passive infrared sensor to detect motion, and only switch on when somebody is passing by in the dark.
What is light sensor in mobile? ›The Ambient Light Sensor is responsible for a common feature on iPhones and Android devices called “Auto Brightness.” This sensor makes it possible for your phone to detect the lighting conditions around you and adjust the screen brightness accordingly.
How do you make a light sensor? ›
How To Make Light Sensor - DIY Automatic Street Light - YouTube
How do you activate a sensor light? ›This is done by turning the light switch OFF – ON – OFF – ON in quick succession. The light will then remain ON and will not go OFF until you manually turn it OFF at the switch. When you're ready to use the sensor again, simply turn the light switch OFF and leave it there for at least a minute.
Is a light sensor input or output? ›A light sensor is an input device that measures light levels.
How do you test a light sensor? ›Light Sensor Test (trouble shooting) - YouTube
What is a light sensor circuit? ›What is a Light Sensor Circuit? The light sensor circuit is a simple electrical circuit, which can be used to control the (switch on and off) electrical load appliances like lights, fans, coolers, air conditioners, street lights, etc., automatically.
How does a motion sensor work? ›A motion sensor uses one or multiple technologies to detect movement in an area. When a sensor detects motion, it sends a signal to your security system's control panel, which connects to your monitoring center. This alerts you and the monitoring center to a potential threat in your home.
Why do we use light at night? ›Light at night allows our primary sense, vision, to operate well. This has benefits for both the individual and for society. These benefits are related to some very basic human motivations. Recognizing these benefits is necessary to limit the use of light at night.
Which sensor is used for motion detection? ›There are two widely used types of motion sensors: active ultrasonic and passive infrared (PIR). Active ultrasonic sensors and passive infrared sensors are the two most common motion sensor technologies, both of which are known for their accuracy and reliability.
Where is the light sensor on a phone? ›The proximity sensor detects when a user is holding the phone near their face during a call and turns off the display to prevent keypad presses and battery consumption from the display. The proximity/light sensor is located to the right of the earpiece.
How many sensors are in a phone? ›The Android smartphone provides two sensors that let you determine position of device- geomagnetic field sensor with combination of accelerometer sensor.
Which sensor is used in mobile phones? ›
Accelerometer. An accelerometer sensor reports the acceleration of the device along the three sensor axes. The measured acceleration includes both the physical acceleration (change of velocity) and the gravity.