I told HAL to dim a light to a certain level, but it doesn't seem to be at the level I requested.

Cause:

HAL wasn't configured to reset the light before it dims it. The X-10 protocol has 16 dim levels, or about one (1) dim level per six percent (6%) of luminance. Dim level 16, for instance, is equal to 96% luminance and dim level 4 is equal to 24% luminance. The X-10 protocol dims lights by subtracting the target dim level from the current dim level. For instance, if a light is at 100% luminance (essentially level 16) and it's told to dim to 25% luminance (level 4), then an X-10 signal is sent commanding the light to drop 12 dim levels (16 - 4 = 12). The problem is that the X-10 signal to drop 12 levels is sent regardless of whether the light was completely on (level 16) or if it was already dimmed. In other words, if the light is at 50% to begin with, it will still be told to drop 12 levels. Because 50% is about level 8, then dropping 12 levels will actually turn the light off.

Solution:

Modify that device so that it resets the light to 100% luminance before it sends the dim command. The light will always dim to the correct level because it's always starting from the same point (100% luminance).  Go to the Automating Your Home section of the Online Help Guide or Operating Manual for more information on specifying dim control of lights.