The LTR390 is one of the few low-cost UV sensors available, and it’s a pretty nice one. With both ambient light and UVA sensing with a peak spectral response between 300 and 350nm. You can use it for measuring how much sun you can get before needing to covering up.
The LTR-390UV-01 is an integrated low voltage 12C ambient light sensor (ALS) and ultraviolet light sensor (UVS). This sensor converts light intensity to a digital output signal capable of direct 12C interface. It provides a linear ALS response over a wide dynamic range, and is well suited to applications under high ambient brightness. The sensor has a programmable interrupt with hysteresis to response to events and that removes the need to poll the sensor for a reading which improves system efficiency. This CMOS design and factory-set one time trimming capability ensure minimal sensor-to-sensor variations for ease of manufacturability to the end customers.
Key Features

13 to 20 bits effective resolutionWide dynamic range of 1:18,000,000 with linear response
Close to human eye spectral response
Automatic rejection for 50Hz/60Hz lighting flicker
PC interface capable of Standard mode @100kHz or Fast mode @400kHz communication; 1.8V logic compatible
Ambient Light / Ultraviolet light (UVS) Technology in one ultra-small 2x2mm ChipLED package
Very low power consumption with sleep mode capability
Operating temperature ranges: -40 to +85 C
Built-in temperature compensation circuit
Programmable interrupt function for ALS, UVS with upper and lower thresholds

STEMMA QT / Qwiic 4-pin 1mm Pitch White Female Connector Cable 150mm Long – Both Sidecan be purchased seperately.
Resources

LTR390 Datasheet

EagleCAD files on GitHub

Fritzing object in the Adafruit Fritzing Library

Adafruit LTR390 UV Sensor