Door Switch
Light Trap
A door switch is mounted on the break side of a door
Alight trap (fig. 4-33) is an arrangement of screens
jamb (inside the compartment) and operated by a stud
placed inside access doors or hatches to prevent the
welded to the door. When the door is opened, the switch
escape of direct or reflected light from within. The
is automatically opened at the same time. Door switches
inside surfaces of the screens are painted fiat black so
are connected in a variety of ways to suit the
that they will reflect a minimum of light falling on them.
arrangement of each compartment.
Light traps that are used to prevent the escape of white
All door-switch installations are provided with
light should have at least two black, light-absorbing
lock-in devices or short-circuiting switches to change
surfaces between the light source and the outboard
the settings of the door switches, as required from
openings. Light traps are preferred to door switches in
lighted ship to darkened ship and vice versa. Each
locations when the following conditions exist:
standard door switch is furnished with a mechanical
lock-in device for use when only one door switch is
1. Egress or ingress is frequent
installed. When two or more door switches are
2. Interruption of light would cause work stoppage
connected in series, a single, separately mounted
in large areas
short-circuiting switch is installed in an accessible
location to avoid the possibility of overlooking any of
3. Light might be exposed from a series of hatches,
the door switches when the changeover is made from
one above the other on successive deck levels
lighted ship to darkened ship and vice versa.
4. Many small compartments and passages are
When a single door switch at an outer door is
joined by numerous inside and outside doors that
would complicate a door-switch installation
connected in parallel with door switches at inner doors,
Figure 4-33.--Light trap.
4-36
