updated docs on plotBrightness (#509)

docs/reference/led/plot-brightness.md

@@ -0,0 +1,63 @@
+# Plot Brightness
+
+Turn on a LED light with a specific brightness on the [LED screen](/device/screen).
+
+```sig
+led.plotBrightness(0,0, 128);
+```
+
+### Parameters
+
+* ``x`` is a [number](/types/number) that means the
+  horizontal spot on the LED screen (from left to right: 0, 1, 2, 3,
+  or 4)
+* ``y`` is a [number](/types/number) that means the vertical
+  spot on the LED screen (from top to bottom: 0, 1, 2, 3, or 4)
+* ``brightness` is a [number](/types/number) that represents the brightness of the LED, from 0 (off) to 255 (full brightness)
+
+If a parameter is [out of bounds](/reference/out-of-bounds) (a value
+other than 0 to 4), then this function will do nothing.
+
+### ~hint
+
+The LED screen is a solid square of LEDs with five LEDs on each side.
+To learn more about how you number the LEDs with ``x`` and ``y``
+coordinates, see [LED screen](/device/screen).
+
+### ~
+
+### Example: One LED
+
+This program turns on the bottom right LED at 50% brightness
+
+```blocks
+led.plotBrightness(2, 2, 128)
+```
+
+
+### Example: Square
+
+This program uses a [for loop](/blocks/loops/for)
+and the `plotBrightness` function
+to make a square around the edges of the LED screen.
+
+```blocks
+for (let i = 0; i < 5; i++) {
+    led.plotBrightness(0, i, 64)
+    led.plotBrightness(4, i, 128)
+    led.plotBrightness(i, 0, 172)
+    led.plotBrightness(i, 4, 255)
+    basic.pause(500)
+}
+```
+
+### ~hint
+
+Use the [point](/reference/led/point) function to find out if an LED is
+on or off.
+
+### ~
+
+### See also
+
+[plot](/reference/led/plot), [unplot](/reference/led/unplot), [point](/reference/led/point), [LED screen](/device/screen)