Section 1 Definition — International

(a) The term height above the hull means height above the uppermost continuous deck. This height shall be measured from the position vertically beneath the location of the light.

(b) The term practical cut-off means the point on an arc around a source of light at which the intensity of the light is reduced as follows:

(i) for vessels of less than 20 metres in length, where the intensity is reduced to 67 per cent of the minimum required intensity within three or five degrees as appropriate, outside the horizontal sectors referred to in section 9 of this Annex and described in Rule 21, practical cut-off occurs at the point at which the intensity is reduced to 10 per cent of the minimum required intensity within 20 degrees outside the horizontal sectors referred to in section 9 of this Annex and described in Rule 21,

(ii) for vessels of 20 metres or more in length, practical cut-off occurs at the point at which the intensity is reduced to 12.5 per cent of the minimum required intensity within three or five degrees, as appropriate, outside the horizontal sectors referred to in section 9 of this Annex and described in Rule 21.