diff --git a/adafruit_si1145.py b/adafruit_si1145.py
index 2b96c64..0ed3068 100644
--- a/adafruit_si1145.py
+++ b/adafruit_si1145.py
@@ -27,51 +27,66 @@
 """
 
 import time
-import struct
 from micropython import const
 from adafruit_bus_device import i2c_device
+from adafruit_register.i2c_struct import Struct
 
 __version__ = "0.0.0-auto.0"
 __repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_SI1145.git"
 
 # Registers
-SI1145_DEFAULT_ADDRESS = const(0x60)
-SI1145_PART_ID = const(0x00)
-SI1145_HW_KEY = const(0x07)
-SI1145_PARAM_WR = const(0x17)
-SI1145_COMMAND = const(0x18)
-SI1145_RESPONSE = const(0x20)
-SI1145_ALS_VIS_DATA0 = const(0x22)
-SI1145_PARAM_RD = const(0x2E)
+_DEFAULT_ADDRESS = const(0x60)
+_PART_ID = const(0x00)
+_HW_KEY = const(0x07)
+_COEFF_0 = const(0x13)
+_COEFF_1 = const(0x14)
+_COEFF_2 = const(0x15)
+_COEFF_3 = const(0x16)
+_PARAM_WR = const(0x17)
+_COMMAND = const(0x18)
+_RESPONSE = const(0x20)
+_ALS_VIS_DATA0 = const(0x22)
+_UV_INDEX_DATA0 = const(0x2C)
+_PARAM_RD = const(0x2E)
 
 # Commands (for COMMAND register)
-SI1145_CMD_PARAM_QUERY = const(0b10000000)
-SI1145_CMD_PARAM_SET = const(0b10100000)
-SI1145_CMD_NOP = const(0b00000000)
-SI1145_CMD_RESET = const(0b00000001)
-SI1145_CMD_ALS_FORCE = const(0b00000110)
+_CMD_PARAM_QUERY = const(0b10000000)
+_CMD_PARAM_SET = const(0b10100000)
+_CMD_NOP = const(0b00000000)
+_CMD_RESET = const(0b00000001)
+_CMD_ALS_FORCE = const(0b00000110)
 
 # RAM Parameter Offsets (use with PARAM_QUERY / PARAM_SET)
-SI1145_RAM_CHLIST = const(0x01)
+_RAM_CHLIST = const(0x01)
 
 
 class SI1145:
     """Driver for the SI1145 UV, IR, Visible Light Sensor."""
 
-    def __init__(self, i2c, address=SI1145_DEFAULT_ADDRESS):
-        self._i2c = i2c_device.I2CDevice(i2c, address)
+    _device_info = Struct(_PART_ID, "<BBB")
+    _ucoeff_0 = Struct(_COEFF_0, "<B")
+    _ucoeff_1 = Struct(_COEFF_1, "<B")
+    _ucoeff_2 = Struct(_COEFF_2, "<B")
+    _ucoeff_3 = Struct(_COEFF_3, "<B")
+    _als_data = Struct(_ALS_VIS_DATA0, "<HH")
+    _aux_data = Struct(_UV_INDEX_DATA0, "<H")
+
+    def __init__(self, i2c, address=_DEFAULT_ADDRESS):
+        self.i2c_device = i2c_device.I2CDevice(i2c, address)
         dev_id, dev_rev, dev_seq = self.device_info
         if dev_id != 69 or dev_rev != 0 or dev_seq != 8:
             raise RuntimeError("Failed to find SI1145.")
         self.reset()
-        self._write_register(SI1145_HW_KEY, 0x17)
+        self._write_register(_HW_KEY, 0x17)
         self._als_enabled = True
-        self.als_enabled = True
+        self._uv_index_enabled = True
+        self.als_enabled = self._als_enabled
+        self.uv_index_enabled = self._uv_index_enabled
 
     @property
     def device_info(self):
         """A three tuple of part, revision, and sequencer ID"""
-        return tuple(self._read_register(SI1145_PART_ID, 3))
+        return self._device_info
 
     @property
     def als_enabled(self):
@@ -80,58 +95,82 @@ def als_enabled(self):
 
     @als_enabled.setter
     def als_enabled(self, enable):
-        chlist = self._param_query(SI1145_RAM_CHLIST)
+        chlist = self._param_query(_RAM_CHLIST)
         if enable:
             chlist |= 0b00110000
         else:
             chlist &= ~0b00110000
-        self._param_set(SI1145_RAM_CHLIST, chlist)
+        self._param_set(_RAM_CHLIST, chlist)
         self._als_enabled = enable
 
     @property
     def als(self):
         """A two tuple of the Ambient Light System (ALS) visible and infrared raw sensor values."""
-        self._send_command(SI1145_CMD_ALS_FORCE)
-        data = self._read_register(SI1145_ALS_VIS_DATA0, 4)
-        return struct.unpack("HH", data)
+        self._send_command(_CMD_ALS_FORCE)
+        return self._als_data
+
+    @property
+    def uv_index_enabled(self):
+        """The UV Index system enabled state"""
+        return self._uv_index_enabled
+
+    @uv_index_enabled.setter
+    def uv_index_enabled(self, enable):
+        chlist = self._param_query(_RAM_CHLIST)
+        if enable:
+            chlist |= 0b01000000
+        else:
+            chlist &= ~0b01000000
+        self._param_set(_RAM_CHLIST, chlist)
+        self._als_enabled = enable
+
+        self._ucoeff_0 = 0x00
+        self._ucoeff_1 = 0x02
+        self._ucoeff_2 = 0x89
+        self._ucoeff_3 = 0x29
+
+    @property
+    def uv_index(self):
+        """The UV Index value"""
+        return self._aux_data[0] / 100
 
     def reset(self):
         """Perform a software reset of the firmware."""
-        self._send_command(SI1145_CMD_RESET)
+        self._send_command(_CMD_RESET)
         time.sleep(0.05)  # doubling 25ms datasheet spec
 
     def clear_error(self):
         """Clear any existing error code."""
-        self._send_command(SI1145_CMD_NOP)
+        self._send_command(_CMD_NOP)
 
     def _param_query(self, param):
-        self._send_command(SI1145_CMD_PARAM_QUERY | (param & 0x1F))
-        return self._read_register(SI1145_PARAM_RD)
+        self._send_command(_CMD_PARAM_QUERY | (param & 0x1F))
+        return self._read_register(_PARAM_RD)
 
     def _param_set(self, param, value):
-        self._write_register(SI1145_PARAM_WR, value)
-        self._send_command(SI1145_CMD_PARAM_SET | (param & 0x1F))
+        self._write_register(_PARAM_WR, value)
+        self._send_command(_CMD_PARAM_SET | (param & 0x1F))
 
     def _send_command(self, command):
-        counter = self._read_register(SI1145_RESPONSE) & 0x0F
-        self._write_register(SI1145_COMMAND, command)
-        if command in (SI1145_CMD_NOP, SI1145_CMD_RESET):
+        counter = self._read_register(_RESPONSE) & 0x0F
+        self._write_register(_COMMAND, command)
+        if command in (_CMD_NOP, _CMD_RESET):
             return 0
-        response = self._read_register(SI1145_RESPONSE)
+        response = self._read_register(_RESPONSE)
         while counter == response & 0x0F:
             if response & 0xF0:
                 raise RuntimeError("SI1145 Error: 0x{:02x}".format(response & 0xF0))
-            response = self._read_register(SI1145_RESPONSE)
+            response = self._read_register(_RESPONSE)
         return response
 
     def _read_register(self, register, length=1):
         buffer = bytearray(length)
-        with self._i2c as i2c:
+        with self.i2c_device as i2c:
             i2c.write_then_readinto(bytes([register]), buffer)
         return buffer[0] if length == 1 else buffer
 
     def _write_register(self, register, buffer):
         if isinstance(buffer, int):
             buffer = bytes([buffer])
-        with self._i2c as i2c:
+        with self.i2c_device as i2c:
             i2c.write(bytes([register]) + buffer)
diff --git a/requirements.txt b/requirements.txt
index a45c547..e429efc 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,3 +4,4 @@
 
 Adafruit-Blinka
 adafruit-circuitpython-busdevice
+adafruit-circuitpython-register