1.4.

The "on" time tH means the period of time within which the luminous intensity
of the flashing light is superior to 1/10 of the maximum value (peak value) Jm.
In case of groups of several flashes the “on” time shall be measured from the beginning of the first flash of the group to the end of the last flash of the same group.

 a4c0
1.4. The "on" time tH means the period of time within which the luminous intensity of the flashing light is superior to 1/10 of the maximum value (peak value) Jm, a0c0