Exit Signs - LEC (Light Emitting Capacitor)

What is electroluminescence?

Electroluminescence occurs when photons (i.e. light) are emitted from a material through excited electrons that are induced by an electrical current or field. In fact, both light emitting diodes (LEDs) and LECs fall under the category of electroluminescence. However, there is a significant difference between the two technologies: LEDs emit light using a direct electrical current through a diode structure which allows current to pass only in one direction, while LECs emit light using an alternating electric field through a capacitor structure which allows for small amounts of leakage current to pass through in two directions. Since power consumption is directly related to how much electrical current is consumed, diode based LEDs use much more energy than capacitive LECs.

What is a light emitting capacitor (LEC)?

The structure of a LEC is very similar to a traditional capacitor, in that there are two conductive plates with a dielectric (non-conductive) material in between them. In a LEC, however, there is an additional layer comprised of a phosphorescent material that can be excited with an electric field to emit light. The type of phosphor used to make the lamp determine the color and wavelength of the light emitted by the LEC. Limelite uses a printing process to pattern the dielectrics, phosphors, and metals onto flexible plastic substrates to create the lamps used in our products. One of the electrode substrates used in LECs is typically a transparent conductor, such as indium tin oxide (ITO), so that the light emitted from the phosphor can be emitted through the surface of the entire capacitor area.

Why electroluminescence?

There are several reasons why LECs are preferable to LED based technologies, especially for safety lighting applications:

1. Energy Efficiency – since LECs use electric fields in a capacitor structure to light up an entire area instead of discrete points of light, less energy is required to produce the requisite amount of light for a properly functioning safety lighting product
2. Visibility – because the entire surface area of the lamp is emitting light, LECs are a much more uniform and visible light source
3. Reliability – LECs can operate at higher temperatures than competing thin film LED technologies (such as OLED)
4. Lifetime – since LECs push less current through the light emitting material and do not need to be run at high wattages, the lifetime of code compliance for safety lighting applications is longer than LED based products