Backlighting - Types
- Phosphorescent
- EL Lamp
- Optical Fiber
- LEDs
- Phosphorescent: This type of passive backlighting offered by GGI International is achieved by adding a layer of phosphorescent material directly under the graphic overlay. When exposed to a source of light (of conventional type or UV), the phosphorescent material stores energy and then, when placed in darkness, releases it in the form of light.
Characteristics:
- Flexible device, 0.010" in thickness
- Colour when idle: green/white
- Colour of emission: green/yellow
- Recharge time: 5 minutes at 1000 lux / 30 minutes at 200 lux
- Light output (after 10 minutes of use in darkness): 51 mcd/m2
- Light output (after 60 minutes of use in darkness): 7.5 mcd/m2
- Duration of continuous illumination: about 10 hours without recharge
- Advantages:
- The phosphorescent material does not require any external source of energy.
- Good resistance to bending
- Uniform lighting
- Simple integration within a membrane switch keypad
- Can take complex forms and include internal cutouts without affecting the uniformity of lighting
- Disadvantages:
- The keypad must initially be exposed to a source of light in order to charge the phosphorescent matter
- The intensity of lighting decreases gradually with time
- The recharge time varies according to the intensity of the source of light
- Colour of emission limited to yellow/green
- Suggested application: GGI International recommends phosphorescent backlighting as a simple and economic solution for keypads that may be placed in darkness for short periods of time.
- Electroluminescent lamp: This type of active backlighting is achieved by adding an electroluminescent lamp, designed and manufactured by GGI, under the graphic overlay. The phosphor-based EL lamp is a condenser with parallel plates that "leak". It is a device which accumulates an electrical charge, then releases it as light.
Characteristics:
- Flexible device, thickness under 0.010"
- Minimum radius: 0.150"
- Operating voltage for most applications: from 60 to 120 VAC RMS (sinusoidal mode)
- Minimum and maximum operating voltage: from 40 to 200 VAC RMS (sinusoidal mode)
- Operating frequencies for most applications: from 400 to 800 Hz
- Minimum and maximum operating frequencies: from 50 to 5000 Hz
- Typical power supply: from 0.01 to 0.06 Watt/in²
- Dielectric strength (tested at 60 Hz): 230 volts (minimum)
- Light output: 24 to 34 cd/m²
- 13 standard colours available: green, blue, aviation green, aviation blue, lime green, amber, yellow, phosphor white, white, bluish white, deep blue, orange and red
- Custom colours available
- Storage temperature: from -40 °C to +90 °C
- Operating temperatures: from -40 °C to +85 °C
- Advantages:
- Good resistance to bending
- Uniform lighting
- Requires little energy
- Low heat emission
- Long lifespan
- Wide number of colours available
- Connection via standard male or female contacts
- Can take complex forms and include internal cutouts without affecting the uniformity of light
- Directional
- Disadvantages:
- DC/AC Inverter is required
- Directional
- Optical fiber: This type of active backlighting offered by GGI International is achieved by adding an optical fiber panel directly under the graphic overlay. The optical fiber panel is composed of one or more layers of optical fibers laminated to a layer of reflective material. The optical fibers are placed next to each other or are interlaced on the reflective material. The overall length of the optical fiber exceeds the surface of the reflective panel in order to form one or more cables. The end of these fibers, which are gathered in a bundle forming a cable, is then further gathered into a brass ferrule. These ferrules are connected to a remote source of light, i.e. LEDs, low intensity incandescent bulbs or halogen bulbs of varying power.
Characteristics:
- Flexible device, minimal thickness of 0.013".
- Minimum required power: 2Vcc - 25 mA
- Light output from an LED
- Lifespan: from 10,000 to 100,000 hours
- Stable at temperatures from -50 °C to 85 °C, in humidity levels from 0% to 100%
- Maximum light surface covered by only one LED: 4" W x 10" L.
- Large variety of colours available, depending on the power source.
- Storage temperature: from -50 °C to 85 °C
- Operating temperatures: from -50 °C to 85 °C
- Advantages:
- Good resistance to bending
- Uniform lighting
- Requires little energy
- No inverter required
- Will not cause EMI interferences
- No heat emission from the optical fiber
- Long lifespan
- Large variety of colours available, depending on the light source
- The light source can be placed remotely from the backlit surface
- Easy maintenance: the panel never needs to be changed; only the light source will be replaced
- Disadvantages:
- Interior space required to install the cable, the ferrule and the light source
- The fiber and the light source must be directed according to the elements to be lit
- Limited in intensity
- Alters the tactile feed back of the switches when laid directly over the domes
- LEDs: This type of active backlighting offered by GGI International is achieved by adding LEDs on a Rigid or Flexible PCB and is installed directly under the diffusing layer (graphic overlay or plastic). A custom engineered diffuser might be required to improve on uniformity. The LEDs normally used on a membrane keypad for illuminating the individual windows can also be used for the backlighting. GGI International's designers are using a state of the art software tool to model and simulate backlighting and can predict exact intensity levels as well as light colour on a pixel scale. The LEDs will provide selective and specific backlighting of certain graphic elements.
Characteristics:
- Typical power requirements: 5V min and between 20mA to 500mA depending on the required surface to illuminate and the brightness desired
- Light output from a LED based solution: ranging from night mode low brightness (1/2 FL or 1 mcd) to day mode high brightness (500FL or more)
- MTBF: from 20,000 to over 100,000 hours
- Large variety of colours available
- Operating temperatures: from -50 °C to 90 °C
- Benefits:
- Selective lighting of individual zones
- Direct integration with the circuit or to the existing PCB
- Will not cause EMI interferences
- Large variety of colours available
- Redundancy (Not a single light source based solution and thus exposure to higher risk of losing the backlighting totally upon failure of the light source is eliminated)
- Higher brightness
- Uniformity
- Selective backlighting
- Totally contained
- Drawbacks:
- Requires a diffusing layer that adds minimal thickness