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Measure Real UVA and Ambient Light in One Compact Sensor
The Adafruit LTR390 UV Light Sensor - STEMMA QT / Qwiic is a compact digital breakout that lets your project detect both UVA light and ambient light levels from a single board. It’s a great choice for sunlight monitoring, UV exposure projects, outdoor sensing, plant-light experiments, and smart devices that react to changing light conditions.
Unlike many basic UV modules, the LTR390 is a true UVA sensor with a dedicated UV-sensitive channel. It also includes internal biasing and ADC circuitry, so you can read data directly over I2C without needing an analog input pin or extra signal-conditioning hardware.
Important: The sensor does not natively output a ready-made UV Index value on its own. Instead, software libraries can convert
the raw UV reading into an estimated UV Index, while ambient light data can be converted into lux.
Why you'll love it
- True UVA sensing: Better than simple visible-light approximations for UV-aware projects
- Ambient light sensing too: Monitor both UV and brightness from one sensor
- Digital I2C interface: Easy to use with Arduino, Raspberry Pi, Feather, ESP32, and more
- No analog pin needed: Internal ADC and biasing are already built in
- 3V and 5V friendly: Onboard regulator and level shifting simplify wiring
- STEMMA QT / Qwiic ready: Fast solderless hookup for I2C builds
- Interrupt pin available: Useful for threshold alerts or event-driven sensing
What you can build
This breakout is ideal for UV exposure meters, sunlight trackers, outdoor data loggers, wearable weather projects, greenhouse monitors, smart blinds, light-reactive installations, and portable devices that need both UV and ambient light awareness.
Starter bundles
Pair it with an Arduino-compatible board, Raspberry Pi, or Adafruit Feather, plus a STEMMA QT cable for quick plug-and-play setup.
Recommended add-ons
Useful add-ons include OLED displays, battery packs, enclosures, microSD logging boards, and other environmental sensors if you want to build a complete weather or sunlight-monitoring station.
Technical specifications
| Product | Adafruit LTR390 UV Light Sensor - STEMMA QT / Qwiic |
|---|---|
| Main Sensor | LTR390 |
| Sensing Modes | UVA sensing and ambient light sensing |
| Peak UV Response | Approximately 300nm to 350nm |
| Interface | I2C |
| Signal Conditioning | Internal biasing and ADC onboard |
| Power Input | 3V to 5V DC |
| Logic Compatibility | 3V to 5V logic via onboard level shifting |
| Connector Type | Dual STEMMA QT / Qwiic-compatible JST SH connectors |
| Extra Pin | INT interrupt output |
Pinout & usage notes
The breakout uses a simple I2C interface with power, ground, SDA, and SCL, plus an INT pin for interrupt-based applications. Because it is fully digital, it works especially well with modern boards that have limited or no analog inputs.
In software, you can read raw UV and ambient light values directly, then use Adafruit’s library routines to derive UV Index and lux when needed.
What’s in the box
1 × Adafruit LTR390 UV Light Sensor breakout
Note: STEMMA QT cable is not included.
Frequently Asked Questions
Does this measure real UV light?
Yes. The LTR390 has a dedicated UVA sensing channel instead of only estimating UV from visible light.
Does it output UV Index directly?
Not by itself. You read the raw UV data, then software can derive a UV Index estimate.
Can I use it with Arduino or Raspberry Pi?
Yes. It uses I2C and is designed for common maker platforms.
Do I need an analog pin?
No. The sensor is fully digital and includes the ADC internally.
Is the QT cable included?
No. The board has STEMMA QT / Qwiic connectors, but the cable is sold separately.
Manila stock. Order before 16:00 PHT, ships today via J&T or LBC. Provincial: 1–3 working days.
Schools / class POs: we accept Purchase Orders for accredited schools and universities. contact us with your PO details.
Returns: 7-day inspection window for DOA units. Email proof of issue and we ship a replacement.
Compatibility & downloads
// downloads
- GitHub PCB repo git
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