diff --git a/NOTES.md b/NOTES.md
index 49fbf67..f69e4ad 100644
--- a/NOTES.md
+++ b/NOTES.md
@@ -1,9 +1,11 @@
-## serial
+## client
+Prefer socat to support arrow keys
 ```
 nc 192.168.1.154 7777
+socat -d -d -,raw,echo=0 TCP:192.168.1.154:7777
 ```
 
-## socat
+## server
 ```
 socat -d -d /dev/ttyACM0,b115200,raw,echo=0 tcp-listen:7777,reuseaddr
 ```
diff --git a/prj.conf b/prj.conf
index 3607be5..45a9875 100644
--- a/prj.conf
+++ b/prj.conf
@@ -20,6 +20,7 @@ CONFIG_UDC_BUF_POOL_SIZE=4096
 # Shell
 CONFIG_SHELL=y
 CONFIG_USBD_SHELL=y
+CONFIG_SHELL_HISTORY=y
 
 # Storage
 CONFIG_NVS=y
diff --git a/src/debug_shell.c b/src/debug_shell.c
index 30725d3..081b032 100644
--- a/src/debug_shell.c
+++ b/src/debug_shell.c
@@ -4,6 +4,7 @@
 #include "mode.h"
 #include "led.h"
 #include "imu.h"
+#include "light.h"
 
 #include <zephyr/shell/shell.h>
 #include <stdlib.h>
@@ -110,6 +111,21 @@ SHELL_STATIC_SUBCMD_SET_CREATE(debug_imu_cmds,
     SHELL_SUBCMD_SET_END
 );
 
+/* --- debug light sensor --- */
+
+static int cmd_dbg_light_read(const struct shell *sh, size_t argc, char **argv)
+{
+    struct light_data_t data;
+    light_read(&data);
+    shell_print(sh, "value=%d", data.value);
+    return 0;
+}
+
+SHELL_STATIC_SUBCMD_SET_CREATE(debug_light_cmds,
+    SHELL_CMD(read, NULL, "Read ambient light sensor value.", cmd_dbg_light_read),
+    SHELL_SUBCMD_SET_END
+);
+
 /* --- top-level debug command --- */
 
 SHELL_STATIC_SUBCMD_SET_CREATE(debug_cmds,
@@ -117,6 +133,7 @@ SHELL_STATIC_SUBCMD_SET_CREATE(debug_cmds,
     SHELL_CMD(led,  &debug_led_cmds,  "PWM LED bar control.",    NULL),
     SHELL_CMD(leds, &debug_leds_cmds, "Addressable LED control.", NULL),
     SHELL_CMD(imu,  &debug_imu_cmds,  "IMU read.",               NULL),
+    SHELL_CMD(light,  &debug_light_cmds,  "Ambient light sensor read.",               NULL),
     SHELL_SUBCMD_SET_END
 );
 
diff --git a/src/light.c b/src/light.c
new file mode 100644
index 0000000..6ab1058
--- /dev/null
+++ b/src/light.c
@@ -0,0 +1,46 @@
+#include "light.h"
+#include "zbus_channels.h"
+
+#include <zephyr/kernel.h>
+#include <zephyr/device.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/drivers/i2c.h>
+
+LOG_MODULE_REGISTER(light, CONFIG_LOG_MAX_LEVEL);
+
+#define ALS_DATA_L 0x1E
+#define DATA_STATUS 0x17 // 0b10000000 mask for data_ready
+
+static const uint8_t i2c_address = 0x38;
+
+static const struct device *const i2c_dev = DEVICE_DT_GET(DT_ALIAS(i2c_1));
+
+int light_init(void)
+{
+	if (!device_is_ready(i2c_dev)) {
+        LOG_ERR("I2C device %s is not ready", i2c_dev->name);
+        return -ENODEV;
+    }
+
+    const uint8_t RESET[2] = {0x00, 0b00000001}; // reset
+    const uint8_t ENABLE_ALS[2] = {0x00, 0b00000001}; // enable ALS
+
+    i2c_write(i2c_dev, RESET,   sizeof(RESET),   i2c_address); k_sleep(K_MSEC(100));
+    i2c_write(i2c_dev, ENABLE_ALS,   sizeof(ENABLE_ALS),   i2c_address); k_sleep(K_MSEC(100));
+
+	return 0;
+}
+
+void light_read(struct light_data_t *buf)
+{
+	uint8_t raw[2];
+	uint16_t reg = ALS_DATA_L;
+
+	int ret = i2c_write_read(i2c_dev, i2c_address, &reg, sizeof(reg), raw, sizeof(raw));
+	if (ret) {
+		LOG_ERR("I2C burst read failed (%d)", ret);
+		return;
+	}
+
+	buf->value = (int16_t)((raw[1] << 8) | raw[0]);
+}
\ No newline at end of file
diff --git a/src/light.h b/src/light.h
new file mode 100644
index 0000000..8098295
--- /dev/null
+++ b/src/light.h
@@ -0,0 +1,13 @@
+#ifndef LIGHT_H
+#define LIGHT_H
+
+#include <zephyr/drivers/gpio.h>
+
+struct light_data_t {
+    uint16_t value;
+};
+
+int light_init(void);
+void light_read(struct light_data_t *buf);
+
+#endif // LIGHT_H
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index 665cb40..eba1c8c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -6,6 +6,7 @@
 #include "config.h"
 #include "imu.h"
 #include "mode.h"
+#include "light.h"
 
 LOG_MODULE_REGISTER(main, LOG_LEVEL_INF);
 
@@ -37,6 +38,12 @@ int main(void)
 		return ret;
 	}
 
+	ret = light_init();
+	if (ret != 0) {
+		LOG_ERR("Failed to init ambient light sensor: %d", ret);
+		return ret;
+	}
+
 	mode_init();
 	mode_start();