Under what conditions do briefly presented flashes yield steeper brightness functions than do flashes of longer duration? The brightness of flashes subtending 2° or 4° and varying in luminance from 216 to 216 cd/m2 were judged by magnitude estimation. Only when durations of 10, 100, and 1,000 msec were randomly intermixed did the short-duration (10-msec) function have a steeper slope; presenting 10-msec durations alone or intermixing 30- and 1,000-msec durations produced no steepening of the short-duration (10- or 30-msec) functions. The steeper brightness functions found for brief flashes in this and previous experiments may be contextually based, that is, dependent upon the presence of longer duration stimuli.