diff --git a/sys/include/phydat.h b/sys/include/phydat.h
index 7a1568a0cc..0a8162c550 100644
--- a/sys/include/phydat.h
+++ b/sys/include/phydat.h
@@ -79,6 +79,8 @@ enum {
     UNIT_TEMP_C,    /**< degree Celsius */
     UNIT_TEMP_F,    /**< degree Fahrenheit */
     UNIT_TEMP_K,    /**< Kelvin */
+    /* illuminance */
+    UNIT_LUX,       /**< Lux (lx) */
     /* dimension */
     UNIT_M,         /**< meters */
     UNIT_M2,        /**< square meters */
diff --git a/sys/phydat/phydat_str.c b/sys/phydat/phydat_str.c
index 431c60361c..7adb4fe6bf 100644
--- a/sys/phydat/phydat_str.c
+++ b/sys/phydat/phydat_str.c
@@ -62,6 +62,7 @@ const char *phydat_unit_to_str(uint8_t unit)
         case UNIT_TEMP_C:   return "°C";
         case UNIT_TEMP_F:   return "°F";
         case UNIT_TEMP_K:   return "K";
+        case UNIT_LUX:      return "lx";
         case UNIT_M:        return "m";
         case UNIT_G:        return "g";
         case UNIT_DPS:      return "dps";