Industrial Design Engineering and the Evolution of LCD Light Source Technology

When you’re a design engineer working on a new, industrial-quality display technology, one of the key issues is light source. When designing an LCD (liquid crystal) display, the engineer has a choice between one of three light-source technologies. Each offers its own strengths and weaknesses in terms of optical performance and operating-temperature range. Here’s the history and how they stack up. A somewhat outmoded technology, the cold cathode fluorescent lamp (CCFL) LCD is positioned horizontally across the rear of the unit, facing backward, and reflects its light off the rear cover. The challenges of designing this type of industrial display are: offsetting the EMI emission; and the unit’s bulk due to the need for an inverter board between its display and power source, plus the physical depth of the lamp. Because of its power inefficiency and lower-quality optics, most manufacturers had replaced CCFL LCD with LED-based technology by the year 2010. Light-emitting diodes, or LED, replaced CCFL as the primary illumination source in LCD displays and, today, LED LCD is the preferred choice for embedded and industrial-market designs. LED requires, on average, just 20 percent of the energy required by CCFL technology, and it’s one of its key benefits. What’s more, LED doesn’t require an inverter board to drive power to the diodes, which enables a smaller, more compact design. LED optics are superior, too. LED LCD is brighter, produces better contrast, and casts its light more evenly across the rear cover. Whereas CCFL emits only white light and presents more modest dimming controls, light-emitting diodes generate RGB color and produce a higher contrast ratio. Organic LED LCD, or OLED, further advances LED technology by integrating light-emitting diodes into each pixel, which enables the pixel to emit its own RGB light naturally. OLED pixels are encapsulated in an organic compound that generates less heat and uses energy more efficiently. Particularly useful in mobile and hand-held applications where optical performance is expected and power is limited, OLED’s primary benefits are: greater power efficiency; the highest-possible contrast ratio of all three technologies discussed; and the capability for true black. Further, by bonding LED and pixel in a super-thin film, the display is transparent, requires even less space than the others, and can be as flexible as a piece of paper. OLED still is expensive to produce because it’s very sensitive to the presence of moisture and oxygen in the manufacturing process. For this reason, just four major manufacturers currently offer industrial-grade OLED LCD technology.