Adafruit
Adafruit LTR390 UV Light Sensor - STEMMA QT / Qwiic
The Adafruit LTR390 is a dual-purpose UV and ambient light sensor with true UVA sensing at a peak spectral response between 300 and 350 nm. Unlike UV index a...
The Adafruit LTR390 is a dual-purpose UV and ambient light sensor with true UVA sensing at a peak spectral response between 300 and 350 nm. Unlike UV index approximation sensors, the LTR390 has a genuine UV photodiode — giving you real ultraviolet light measurements over a simple I2C interface.
The sensor also provides ambient light readings, making it useful for both UV exposure monitoring and general light level detection. The biasing and ADC are all internal, so no external components are needed. This STEMMA QT breakout includes voltage regulation and level shifting for both 3.3 V and 5 V systems.
Key Features
- True UVA Sensing – Real UV photodiode with peak response at 300–350 nm
- Ambient Light Sensing – Dual-mode sensor for both UV and visible light measurements
- Internal ADC – No external analogue-to-digital converter required
- I2C Interface – Simple two-wire communication
- STEMMA QT / Qwiic – Solderless I2C connectors for easy plug-and-play wiring
- 3.3 V and 5 V Compatible – Onboard voltage regulator and level shifting
Ideal For
- UV exposure monitoring and sun safety projects
- Weather stations with UV index estimation
- Ambient light sensing and display brightness control
- Environmental monitoring and wearable UV trackers
Package Contents
- 1× Adafruit LTR390 UV Light Sensor Breakout (STEMMA QT)
Resources
Jargon buster
Plain-language definitions for the technical terms used above.
- ADC
- An analogue-to-digital converter reads a changing voltage and turns it into a number the microcontroller can use. It matters when connecting analogue sensors such as light, sound, or variable-resistor sensors.
- Ambient light sensor
- A sensor that measures the general brightness of light falling on it, similar to how a device can adjust screen brightness automatically. It matters when you want a project to react to room lighting, daylight, shadows, or covered/uncovered conditions.
- breakout
- A breakout is a small circuit board that makes a tiny or hard-to-solder component easier to connect to with standard pins. It matters because this OLED module can be wired into a microcontroller project without needing to solder directly to the display’s fine contacts.
- I2C
- I2C is a two-wire communication bus used by many sensors and small modules. It matters because several I2C devices can share the same two wires, but each device needs a compatible address and your controller must support I2C.
- photodiode
- A photodiode is a light-sensitive electronic component that produces a signal when light hits it. In this sensor, multiple photodiodes let the chip measure different parts of the light spectrum separately.
- Qwiic
- Qwiic is a plug-in connector system for I2C devices that uses small 4-pin cables, so you can connect compatible sensors without soldering. It matters because your controller or adapter also needs Qwiic, or you will need a cable or breakout to wire it up.
- STEMMA
- A plug-and-cable connection system used on some maker electronics boards to make wiring simpler. If a product uses STEMMA, you need the matching cable or connector type to plug it in without soldering.
- STEMMA QT
- A small plug-in connector system for I2C boards that lets you connect compatible sensors and controllers without soldering. It matters because it can make wiring faster and less error-prone, especially when adding several small modules to a project.
- Torque
- A twisting force that causes something to rotate, usually measured in newton-metres or kilogram-centimetres. It matters when choosing motors, servos, gears, and tools because higher torque is needed to lift heavier loads, turn larger wheels, or move mechanisms without stalling.
- UVA
- UVA is the longer-wavelength part of ultraviolet light, closest to visible violet light. Measuring it separately matters when you need to distinguish general UV exposure from the more energetic UVB and UVC bands.
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Related Tutorials
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