diff --git a/src/renderkit/logging_utils.py b/src/renderkit/logging_utils.py
index 10c391e..1b3e405 100644
--- a/src/renderkit/logging_utils.py
+++ b/src/renderkit/logging_utils.py
@@ -40,6 +40,13 @@ def _has_handler(logger: logging.Logger, handler_key: str) -> bool:
     )
 
 
+def _get_handler(logger: logging.Logger, handler_key: str) -> logging.Handler | None:
+    for handler in logger.handlers:
+        if getattr(handler, "renderkit_handler", None) == handler_key:
+            return handler
+    return None
+
+
 def _log_level() -> int:
     level_name = os.environ.get("RENDERKIT_LOG_LEVEL", "INFO").upper()
     return getattr(logging, level_name, logging.INFO)
@@ -92,7 +99,8 @@ def setup_logging(
     )
 
     # 3. Manage File Handler
-    if not _has_handler(root_logger, "file"):
+    file_handler = _get_handler(root_logger, "file")
+    if file_handler is None:
         file_handler = RotatingFileHandler(
             log_path,
             maxBytes=5 * 1024 * 1024,
@@ -100,10 +108,10 @@ def setup_logging(
             encoding="utf-8",
         )
         file_handler.renderkit_handler = "file"
-        file_handler.setLevel(logging.INFO)  # File captures INFO+
         file_handler.setFormatter(file_formatter)
         root_logger.addHandler(file_handler)
         rk_logger.info("Logging to %s", log_path)
+    file_handler.setLevel(log_level)
 
     # 4. Manage Console Handler
     if enable_console is None:
diff --git a/tests/conftest.py b/tests/conftest.py
index b525477..13049e8 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,10 +1,28 @@
 """Shared pytest fixtures for RenderKit tests."""
 
+import logging
+
 import pytest
 
 from renderkit.ui.qt_compat import QApplication
 
 
+def _close_renderkit_logging_handlers() -> None:
+    root_logger = logging.getLogger()
+    for handler in root_logger.handlers.copy():
+        if getattr(handler, "renderkit_handler", None):
+            root_logger.removeHandler(handler)
+            handler.close()
+
+
+@pytest.fixture(autouse=True)
+def cleanup_renderkit_logging_handlers():
+    """Keep RenderKit root handlers from leaking between tests."""
+    _close_renderkit_logging_handlers()
+    yield
+    _close_renderkit_logging_handlers()
+
+
 @pytest.fixture(scope="session")
 def qapp():
     """Create a QApplication for Qt widget tests."""
diff --git a/tests/test_logging_utils.py b/tests/test_logging_utils.py
new file mode 100644
index 0000000..145653e
--- /dev/null
+++ b/tests/test_logging_utils.py
@@ -0,0 +1,62 @@
+"""Tests for RenderKit logging helpers."""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+
+from renderkit.logging_utils import setup_logging
+
+
+def _flush_renderkit_handlers() -> None:
+    for handler in logging.getLogger().handlers:
+        if getattr(handler, "renderkit_handler", None):
+            handler.flush()
+
+
+def test_env_debug_level_reaches_file_log(monkeypatch, tmp_path: Path) -> None:
+    """RENDERKIT_LOG_LEVEL should control the file sink level."""
+    log_path = tmp_path / "renderkit-debug.log"
+    monkeypatch.setenv("RENDERKIT_LOG_PATH", str(log_path))
+    monkeypatch.setenv("RENDERKIT_LOG_LEVEL", "DEBUG")
+
+    setup_logging(enable_console=False)
+    logging.getLogger("renderkit.test").debug("debug sentinel")
+    logging.getLogger("renderkit.test").info("info sentinel")
+    _flush_renderkit_handlers()
+
+    log_text = log_path.read_text(encoding="utf-8")
+    assert "debug sentinel" in log_text
+    assert "info sentinel" in log_text
+
+
+def test_explicit_debug_level_reaches_file_log(monkeypatch, tmp_path: Path) -> None:
+    """The explicit setup_logging level should control the file sink."""
+    log_path = tmp_path / "renderkit-explicit-debug.log"
+    monkeypatch.setenv("RENDERKIT_LOG_PATH", str(log_path))
+    monkeypatch.setenv("RENDERKIT_LOG_LEVEL", "INFO")
+
+    setup_logging(enable_console=False, level=logging.DEBUG)
+    logging.getLogger("renderkit.test").debug("explicit debug sentinel")
+    _flush_renderkit_handlers()
+
+    log_text = log_path.read_text(encoding="utf-8")
+    assert "explicit debug sentinel" in log_text
+
+
+def test_reconfigured_debug_level_updates_existing_file_handler(
+    monkeypatch, tmp_path: Path
+) -> None:
+    """Repeated setup should update the existing file handler level."""
+    log_path = tmp_path / "renderkit-reconfigured-debug.log"
+    monkeypatch.setenv("RENDERKIT_LOG_PATH", str(log_path))
+
+    setup_logging(enable_console=False, level=logging.INFO)
+    logging.getLogger("renderkit.test").debug("hidden debug sentinel")
+    setup_logging(enable_console=False, level=logging.DEBUG)
+    logging.getLogger("renderkit.test").debug("updated debug sentinel")
+    _flush_renderkit_handlers()
+
+    log_text = log_path.read_text(encoding="utf-8")
+    assert "hidden debug sentinel" not in log_text
+    assert "updated debug sentinel" in log_text