diff --git a/README.md b/README.md
index 887d259..3f77e45 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,9 @@ stairs show. On exit it sends a black frame. The stairs power must be on
     nix-shell --run "python treppe_gl.py shaders/flow.glsl"
     nix-shell --run "python treppe_gl.py shaders/pulse.glsl --dry-run"
 
-Options: `--host`, `--port`, `--fps`, `--dry-run` (send nothing),
+Wrappers: `./treppe-run.sh <shader> [brightness]` and `./treppe-dry.sh <shader> [brightness]` (dry run, nothing is sent).
+
+Options: `--brightness 0-100` (scales output, default 100), `--host`, `--port`, `--fps`, `--dry-run` (send nothing),
 `--no-window` (headless), `--white {extract,alpha,off}`.
 
 Shaders define `mainImage(out vec4 fragColor, in vec2 fragCoord)` and may
diff --git a/tests/test_treppe_gl.py b/tests/test_treppe_gl.py
index 7c982c9..cae6c2e 100644
--- a/tests/test_treppe_gl.py
+++ b/tests/test_treppe_gl.py
@@ -59,3 +59,12 @@ def test_udp_loopback():
     tx = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     tx.sendto(t.BLACK_FRAME, rx.getsockname())
     assert rx.recv(2048) == t.BLACK_FRAME
+
+
+def test_brightness_scales_and_clamps():
+    px = np.array([[1.0, 0.5, 0.25, 1.0]] + [[0, 0, 0, 0]] * 15)
+    half = t.to_rgbw(px, "extract", 50)[0]
+    np.testing.assert_allclose(half, [0.375, 0.125, 0.0, 0.125])
+    assert t.to_rgbw(px, "extract", 0).max() == 0
+    np.testing.assert_allclose(t.to_rgbw(px, "extract", 500),
+                               t.to_rgbw(px, "extract", 100))
diff --git a/treppe-dry.sh b/treppe-dry.sh
new file mode 100755
index 0000000..ef57b40
--- /dev/null
+++ b/treppe-dry.sh
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+# Usage: treppe-dry.sh <shader.glsl> [brightness 0-100, default 100]
+set -euo pipefail
+here=$(dirname "$(realpath "$0")")
+[ $# -ge 1 ] || { echo "usage: $0 <shader.glsl> [brightness 0-100]" >&2; exit 2; }
+shader=$(realpath "$1")
+cd "$here"
+exec nix-shell --run "python treppe_gl.py '$shader' --brightness ${2:-100} --dry-run"
diff --git a/treppe-run.sh b/treppe-run.sh
new file mode 100755
index 0000000..a17f896
--- /dev/null
+++ b/treppe-run.sh
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+# Usage: treppe-run.sh <shader.glsl> [brightness 0-100, default 100]
+set -euo pipefail
+here=$(dirname "$(realpath "$0")")
+[ $# -ge 1 ] || { echo "usage: $0 <shader.glsl> [brightness 0-100]" >&2; exit 2; }
+shader=$(realpath "$1")
+cd "$here"
+exec nix-shell --run "python treppe_gl.py '$shader' --brightness ${2:-100}"
diff --git a/treppe_gl.py b/treppe_gl.py
index 061e214..6e9db2d 100644
--- a/treppe_gl.py
+++ b/treppe_gl.py
@@ -35,23 +35,26 @@ WHITE_MODES = ("extract", "alpha", "off")
 
 # --- Protocol --------------------------------------------------------------
 
-def to_rgbw(pixels, white="extract"):
+def to_rgbw(pixels, white="extract", brightness=100.0):
     """
     Convert float RGBA pixels (STEPS x 4, 0..1) to RGBW (STEPS x 4).
 
     extract: w = min(r, g, b), subtracted from r, g, b
     alpha:   the shader's alpha channel is the white value
     off:     w = 0
+
+    brightness (0..100, percent) scales the result linearly.
     """
+    scale = np.float32(min(max(brightness, 0.0), 100.0) / 100.0)
     px = np.clip(np.asarray(pixels, dtype=np.float32), 0.0, 1.0)
     rgb = px[:, :3]
     if white == "extract":
         w = rgb.min(axis=1, keepdims=True)
-        return np.hstack([rgb - w, w])
+        return np.hstack([rgb - w, w]) * scale
     if white == "alpha":
-        return np.hstack([rgb, px[:, 3:4]])
+        return np.hstack([rgb, px[:, 3:4]]) * scale
     if white == "off":
-        return np.hstack([rgb, np.zeros((len(px), 1), dtype=np.float32)])
+        return np.hstack([rgb, np.zeros((len(px), 1), dtype=np.float32)]) * scale
     raise ValueError("unknown white mode: {}".format(white))
 
 
@@ -380,7 +383,7 @@ def run(args):
             last = now
 
             pixels = renderer.render_strip(t, dt, frame)
-            rgbw = to_rgbw(pixels, args.white)
+            rgbw = to_rgbw(pixels, args.white, args.brightness)
             if sock:
                 sock.sendto(encode_frame(rgbw), target)
 
@@ -414,6 +417,8 @@ def parse_args(argv=None):
     p.add_argument("--port", type=int, default=PORT_DEFAULT)
     p.add_argument("--fps", type=float, default=60.0)
     p.add_argument("--white", choices=WHITE_MODES, default="extract")
+    p.add_argument("--brightness", type=float, default=100.0,
+                   help="0..100 percent, scales what is sent (default 100)")
     p.add_argument("--dry-run", action="store_true",
                    help="do not send anything over the network")
     p.add_argument("--no-window", dest="window", action="store_false",