**Sec. 25.1389 - Position light distribution and intensities.**
(a) *General.* The intensities
prescribed in this section must be provided by new equipment with light
covers and color filters in place. Intensities must be determined with the
light source operating at a steady value equal to the average luminous
output of the source at the normal operating voltage of the airplane. The
light distribution and intensity of each position light must meet the
requirements of paragraph (b) of this section.

(b) *Forward and rear position lights.*
The light distribution and intensities of forward and rear position lights
must be expressed in terms of minimum intensities in the horizontal plane,
minimum intensities in any vertical plane, and maximum intensities in
overlapping beams, within dihedral angles *L, R,* and *A,* and
must meet the following requirements:

(1) *Intensities in the horizontal
plane.* Each intensity in the horizontal plane (the plane containing
the longitudinal axis of the airplane and perpendicular to the plane of
symmetry of the airplane) must equal or exceed the values in §25.1391.

(2) *Intensities in any vertical
plane.* Each intensity in any vertical plane (the plane perpendicular
to the horizontal plane) must equal or exceed the appropriate value in
§25.1393, where *I* is the minimum intensity prescribed in §25.1391
for the corresponding angles in the horizontal plane.