diff --git a/src/ipa/libipa/lux.cpp b/src/ipa/libipa/lux.cpp
new file mode 100644
index 00000000..756cd3c4
--- /dev/null
+++ b/src/ipa/libipa/lux.cpp
@@ -0,0 +1,119 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2019, Raspberry Pi Ltd
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * lux.h - Helper class that implements lux estimation
+ */
+#include "lux.h"
+
+#include <algorithm>
+#include <chrono>
+
+#include <libcamera/base/log.h>
+
+#include "libcamera/internal/yaml_parser.h"
+
+#include "histogram.h"
+
+/**
+ * \file lux.h
+ * \brief Helper class that implements lux estimation
+ *
+ * As estimating the lux level of an image is expected to be a common
+ * operation, it is implemented in a helper in libipa.
+ */
+
+namespace libcamera {
+
+using namespace std::literals::chrono_literals;
+
+LOG_DEFINE_CATEGORY(Lux)
+
+namespace ipa {
+
+/**
+ * \class Lux
+ * \brief Class that implements lux estimation
+ */
+
+/**
+ * \var Lux::referenceExposureTime_
+ * \brief The exposure time of the reference image, in microseconds.
+ */
+
+/**
+ * \var Lux::referenceGain_
+ * \brief The analogue gain of the reference image.
+ */
+
+/**
+ * \var Lux::referenceAperture_
+ * \brief The aperture of the reference image in units of 1/f.
+ */
+
+/**
+ * \var Lux::referenceY_
+ * \brief The measured luminance of the reference image, out of 65536.
+ */
+
+/**
+ * \var Lux::referenceLux_
+ * \brief The estimated lux level of the reference image.
+ */
+
+int Lux::readYaml(const YamlObject &tuningData)
+{
+	auto value = tuningData["reference_exposure_time"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: 'reference_exposure_time'";
+		return -EINVAL;
+	}
+	referenceExposureTime_ = *value * 1.0us;
+
+	value = tuningData["reference_gain"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: 'reference_gain'";
+		return -EINVAL;
+	}
+	referenceGain_ = *value;
+
+	referenceAperture_ = tuningData["reference_aperture"].get<double>(1.0);
+
+	value = tuningData["reference_Y"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: 'reference_Y'";
+		return -EINVAL;
+	}
+	referenceY_ = *value;
+
+	value = tuningData["reference_lux"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: 'reference_lux'";
+		return -EINVAL;
+	}
+	referenceLux_ = *value;
+
+	return 0;
+}
+
+double Lux::process(double gain, utils::Duration exposureTime, double aperture,
+		    const Histogram &yHist) const
+{
+	double currentY = yHist.interQuantileMean(0, 1);
+	double gainRatio = referenceGain_ / gain;
+	double exposureTimeRatio = referenceExposureTime_ / exposureTime;
+	double apertureRatio = referenceAperture_ / aperture;
+	double yRatio = currentY * (65536 / yHist.bins()) / referenceY_;
+
+	double estimatedLux = exposureTimeRatio * gainRatio *
+			      apertureRatio * apertureRatio *
+			      yRatio * referenceLux_;
+
+	LOG(Lux, Debug) << "Estimated lux " << estimatedLux;
+	return estimatedLux;
+}
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/lux.h b/src/ipa/libipa/lux.h
new file mode 100644
index 00000000..6bc9cf9f
--- /dev/null
+++ b/src/ipa/libipa/lux.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2019, Raspberry Pi Ltd
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * lux.h - Helper class that implements lux estimation
+ */
+
+#pragma once
+
+#include <algorithm>
+#include <tuple>
+#include <vector>
+
+#include <libcamera/base/utils.h>
+
+#include "libcamera/internal/yaml_parser.h"
+
+#include "histogram.h"
+
+namespace libcamera {
+
+namespace ipa {
+
+class Lux
+{
+public:
+	Lux() = default;
+	~Lux() = default;
+
+	int readYaml(const YamlObject &tuningData);
+	double process(double gain, utils::Duration exposureTime,
+		       double aperture, const Histogram &yHist) const;
+
+private:
+	utils::Duration referenceExposureTime_;
+	double referenceGain_;
+	double referenceAperture_;
+	double referenceY_;
+	double referenceLux_;
+};
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
index 0796982e..b6d58900 100644
--- a/src/ipa/libipa/meson.build
+++ b/src/ipa/libipa/meson.build
@@ -8,6 +8,7 @@ libipa_headers = files([
     'exposure_mode_helper.h',
     'fc_queue.h',
     'histogram.h',
+    'lux.h',
     'matrix.h',
     'module.h',
     'pwl.h',
@@ -21,6 +22,7 @@ libipa_sources = files([
     'exposure_mode_helper.cpp',
     'fc_queue.cpp',
     'histogram.cpp',
+    'lux.cpp',
     'matrix.cpp',
     'module.cpp',
     'pwl.cpp'