Not long ago I was bemoaning the fact that so many boatbuilders are still using highly inefficient incandescent and halogen lights, even though fluorescent lights have long been available and LEDs are now viable for most marine lighting applications. Since then, Neil Harrison, a reader from the UK, has pointed out that the next revolution in lighting may already be on the horizonOrganic Light-Emitting Diodes, or OLEDs.
Before getting into this, lets look first at the currently available technologies. Efficiency is not the only critical factor. Equally important are the beam angle, the color temperature, the color rendering index score, life expectancy in the marine environment and, of course, cost.
EFFICIENCY AND BEAM ANGLE
The efficiency of a light source is typically measured in terms of lumens of light output per watt of electricity consumed. Incandescent lights are generally below 10 lumens per watt, halogens around 15 lumens per watt, fluorescents between 50 and 100 lumens per watt, and LEDs anywhere from 20 lumens per watt to 60 lumens per watt, with the efficiency improving every year (in the laboratory LEDs rate at well over 100 lumens per watt).
Traditional light sources tend to radiate in all directions, but usually we want light projected in a specific direction, for example from the ceiling downward. If two lights are equally efficient, but one scatters light in all directions while the other projects it solely where we want it, the latter can be a lower-power fixture and therefore more efficient. Incandescents, halogens and fluorescents all scatter their light. LEDs concentrate it into a defined beam. In practice, an LED that puts out 60 lumens per watt is generally significantly more efficient than even a fluorescent running at 100 lumens per watt.
Lighting is described as warm or cold. Warm light tends toward the red end of the light spectrum, while cool tends toward the blue end. Warmth can also be expressed in degrees Kelvin, or K. Warm light has a color temperature of around 2,700K to 3,000K. Cool light is 4,000K and higher. For interior boat lighting, we typically want something on the order of 2,700K to 3,000K. Most incandescent and halogen lighting is between 2,500K and 3,100K. Traditional fluorescent office lighting is around 4,000K, which is on the cold side, although compact fluorescents are now widely available with color temperatures as low as 2,700K. (The color temperature is generally given in the small print on the packaging.)
White LEDs actually create a very cold blue light that excites a phosphor coating on the inside of the LEDs lens. This coating is doped with optically active ions that convert some of the blue light into yellow light. The resulting blue-yellow mix is seen as white light. Most white LEDs are above 4,000K, and as such give a relatively cold light.
Although warmer lights with lower color temperatures are easier on the eyes, their light is less efficientwarmer LEDs are typically only 70 percent as efficient as cooler LEDs. Researchers are currently trying to manipulate LED phosphors in a way that will add red light to lower the color temperature without a loss of efficiency.
Another factor to consider when evaluating light quality is the ability of a light source to illuminate an objects colors, as they would be seen under a natural light source. This is expressed through something known as the color rendering index, or CRI. Natural light has a CRI of 100. As the quality of light degrades, the CRI goes down. If the CRI is below 90, colors start to look unnatural to the human eye. Most incandescent and halogen lights have a CRI of 100. Compact fluorescents are usually around 90, although some are as high as 95. Most white LEDs are between 70 and 80, yielding a significant degradation of light quality, although some LEDs are now available with CRIs up to 90. One of the reasons for the low CRI of LEDs is the difficulty of ensuring a uniform mix of the blue and yellow light over the entire illuminated area.
The life expectancies of the various forms of marine lighting vary enormously from what is achieved in the laboratory. This is primarily a function of the widely variable voltage on DC systems. A typical 12-volt system, for example, may range from as low as 11.0 volts when it is seriously discharged or under a heavy load to as high as 14.4 volts during the absorption phase of battery charging.
Halogens, in particular, suffer a sharp loss of life at the higher end of the voltage scale. LEDs in the raw state are also extremely sensitive to high voltage, and must be coupled with a driver that acts as a voltage regulator. The life expectancy of an LED is substantially dependent on the quality and sophistication of its driver. The latest drivers are incredibly sophisticated.
In general, the life expectancy of incandescents and halogens is measured in the low thousands of hours, while fluorescents can last tens of thousands of hours. LEDs vary, but can last as long as 50,000 hours.
The primary reason most boatbuilders still use incandescents and halogens is because of the relatively low purchase price. This, of course, is no measure of real cost, which must include efficiency and life expectancy. In this respect, fluorescents are particularly cost-effective. Meanwhile, the cost per lumen of light output from LEDs has decreased rapidly in recent years, while the gap with fluorescents is closing. If I were to build a boat today, I would seriously consider all-LED lighting. My current boat has fluorescent area lighting and LED reading and task lighting.
The OLED Revolution
An OLED has a very thin layer of organic material sandwiched between a negative and positive electrode layer. The whole thing is no thicker than several sheets of paper, less than 1 mm. When an electric charge is applied, the organic material is excited and produces light. These are the first electric lights that do not create a point source of light. Instead, a sheet of light is generated. Initially, OLEDs will be produced in panels of various sizes, but in time they will probably be coated onto walls, ceilings and other surfaces. If successful, OLEDs will radically change lighting and interior design concepts.
Predictions are that OLEDs can achieve higher efficiencies than even LEDs (currently, OLEDs produce up to 64 lumens per watt), with the necessary color temperatures, CRI, life expectancy and cost effectiveness to be viable. We shall have to wait and see. General Electric and Konica Minolta are leading the charge on OLEDs. Konica Minolta plans to open its first mass production facility later this year, with commercialization predicted for 2011.
It could be that by the time most boatbuilders finally get on the LED bandwagon, they will already be obsolete.