Basic
/ Transition
of Incandescent to LED technology on the Flight Deck
IDD Design
and Test Capabilities /
Design
and Production
What is MIL-P-7788
or SAE AS7788?
This document is the governing specification
for the construction and manufacture of lightplates. MIL-P-7788
was originally released as a military standard but in 1999 the maintenance
of the specification was taken over by SAE and the document number
was changed to SAE AS7788.
What is a lightplate?
A lightplate is also referred to as an illuminated
panel, lighted plate or an edgelit panel. Most panels in production
today are either Type V (incandescent) or Type VII (LED). These
panels generally consist of a circuit board with a power connector
and lamps attached to a painted acrylic panel which reflects and
emits the light according to the specification for the installation
environment. A lightplate is used in the flight deck to illuminate
knobs and identify various controls with illuminated logic lines
and words indicating functions. Generally lightplates are manufactured
to SAE AS7788, but other customer requirements can be incorporated
to address specific flight deck specifications including night vision
compatibility.
What are the different
types of lightplates?
Lightplates can be broken down into 5 main
types as defined in SAE AS7788.
| Type III |
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One piece plastic panels. These panels typically
use front replaceable post lamps for illumination. This type
of panel is inactive for new designs. |
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| Type IV |
|
One piece integrally wired panels. These panels have the lighting
circuit and lamps embedded within the panel. They are commonly
referred to as embedded panels. This type of panel is normally
not used for new designs. |
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| Type V |
|
Printed circuit board panels. These panels have the lighting
circuit and incandescent lamps on a separate circuit board.
This is the most common panel currently in production. |
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| Type VI |
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Electroluminescent Panels. These panels feature and encapsulated
electroluminescent lamp. Due to limited electroluminescent life,
these panels have limited applications for new designs. |
| |
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| Type VII |
|
Light Emitting Diode (LED) panels. These panels have the lighting
circuit and LED’s on a separate circuit board. This type
of panel is the most common panel for new fight deck applications. |
Does IDD manufacture
electroluminescent lightplates or bezels?
IDD currently manufactures several electroluminescent
bezels. Over the past several years IDD has helped convert most
of our customers to high life and high reliability LED technologies
through an LED to EL conversion circuit embedded in the panel. This
circuit achieves a form, fit and function replacement with no change
required on the aircraft. Due to their relatively short life (fading
after approximately 8000 hours), and the special handling required
for production, EL lamps are no longer the technology of choice
for low heat, high vibration, or low power applications in new applications.
How does the pilot
control the level of illumination of the panels on the flight deck?
The illumination level is controlled via
power regulation from the lighting dimming controller unit/units
to each illuminated panel. As the pilot dims or brightens the panels
via a single control or control per logical area in the cockpit,
the dimming controller units send out a uniform amount of current
to each panel to achieve consistency in lighting for brightness
and uniformity.
How are lightplates
manufactured?
IDD designs lightplates using a CAD/CAM system
for modeling. CNC milling centers are used to machine acrylic panels
and the circuit board. Automated paint machines and patented CCD
camera/computer systems are used for applying the paint. Indicia
(panel legends, logos and graphics) are applied using a patented
laser etching process. Spectroradiometers and/or photometers are
used for color and luminance verification throughout the production
process. These highly automated processes optimize production for
consistency in quality year over year at a competitive price.
What is an ISP?
ISP stands for Integrated or Illuminated
Switch Panel. IDD uses this abbreviation for panels (lightplates)
that have switches built into them. Generally they are used as bezels
and keyboards, although, IDD manufactures an array of custom Human
Machine Interface panels. Similar high volume precision manufacturing
processes are used for lightplates and integrated switch panels.
What are the key
attributes of switch actuation?
The two most commonly defined aspects of
switch actuation are pre-travel and force. The pre-travel is the
distance the button moves before the switch actuates. The force
is the amount of force that must be applied to the pushbutton before
it actuates. Additional characteristics that are sometimes defined
are over travel, residual force, and total travel.
What is a Control
Panel Assembly?
Control Panel Assemblies generally consist
of lightplates with toggle switches, pushbutton illuminated switches,
circuit breakers, and PWBs assembled and wired to standoff connectors.
A trend for these assemblies is the inclusion of digital interfaces
into the control panels to minimize wiring and reduce weight. These
assemblies are also referenced as ICPs or (Integrated Control Panels).
An additional emerging trend is the outsourcing
of the design, documentation, engineering development and assembly
of these panels by avionics and airframe manufacturers to companies
that focus on human machine interface and lighting assemblies within
the aerospace industry.
What is LED Technology?
The term LED is short for light emitting
diode, a diode that produces light. LED’s are actually semiconductor
chips made from silicone laced with elements like gallium. When
low voltage electricity is passed through the microchip, it gives
off a light. The material that the silicone is laced with determines
the color of the light.
Why are Incandescent
lamps less reliable?
Incandescent lights have been around since
1879, when Thomas Edison first introduced them. They work because
of a very simple principle called incandescence, the production
of light by a hot object. Incandescent bulbs use a filament normally
made of tungsten. The filament is not a good conductor of electricity
so when you pass electricity through the filament, it gets hot and
glows. The glowing makes the light. This is similar to the glowing
of the coils of an electric range, or a heating element in a toaster.
(The heat is what leads to the higher touch temperature of incandescent
pushbuttons and switches vs. LED.)
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