diff --git a/doc/user_guide/supported_formats/hamamatsu.rst b/doc/user_guide/supported_formats/hamamatsu.rst
index 1d747f958..e800dbb16 100644
--- a/doc/user_guide/supported_formats/hamamatsu.rst
+++ b/doc/user_guide/supported_formats/hamamatsu.rst
@@ -5,18 +5,20 @@ Hamamatsu
 
 Reader for spectroscopy data saved in ``.img`` (ITEX) files from the HPD-TA
 (High Performance Digital Temporal Analyzer) or HiPic (High Performance image control)
-softwares from Hamamatsu, e.g. for streak cameras or high performance CCD cameras.
+softwares from Hamamatsu, e.g. for images from streak cameras or high performance
+CCD cameras.
 
-If `LumiSpy <https://lumispy.org>`_ is installed, ``Luminescence`` will be
-used as the ``signal_type``.
+If `LumiSpy <https://lumispy.org>`_ is installed, ``TransientSpec`` will be
+used as the ``signal_type``, which is intended for streak camera images with
+both wavelength and time axes.
 
 .. Note::
 
-   Reading files containing multiple channels or multiple images per channel
-   is not implemented.
+   Currently, reading files containing multiple channels or multiple images per
+   channel is not implemented.
 
 API functions
 ^^^^^^^^^^^^^
 
 .. automodule:: rsciio.hamamatsu
-   :members:
\ No newline at end of file
+   :members:
diff --git a/rsciio/hamamatsu/_api.py b/rsciio/hamamatsu/_api.py
index 77cc5f9b3..5f911c56d 100644
--- a/rsciio/hamamatsu/_api.py
+++ b/rsciio/hamamatsu/_api.py
@@ -497,7 +497,9 @@ def map_metadata(self):
 
 def file_reader(filename, lazy=False, use_uniform_signal_axes=False, **kwds):
     """
-    Read Hamamatsu's ``.img`` file.
+    Read Hamamatsu's ``.img`` file, e.g. for streak camera images. In case
+    LumiSpy is installed, the signal type is automatically set to
+    ``TransientSpec``.
 
     Parameters
     ----------
diff --git a/upcoming_changes/209.bugfix.rst b/upcoming_changes/209.bugfix.rst
new file mode 100644
index 000000000..d88c38aa1
--- /dev/null
+++ b/upcoming_changes/209.bugfix.rst
@@ -0,0 +1 @@
+Set ``signal_type`` to ``TransientSpec`` when Hamamatsu ``.img`` files are read and LumiSpy is installed.