LEDs and Contrast Threshold: More than Just Energy Efficiency|
While much of the focus on Marine lighting has lately been on the reduced energy usage benefits switching to LED’s from Halogens represents, there is more to the story than just prolonging the charge time of your crafts batteries. If you search the internet or read the magazines dedicated to boating, you’re likely to see all sorts of stories touting the great reductions in electrical drain on a boats energy reserves that LED’s produce and little else. While this is definitely true and certainly worth talking about, LEDs offer more than just a way to improve the electrical efficiency of your crafts lighting systems.
One of the most often heard complaints associated with a Halogen bulb is that the color of the light it produces is yellowish. This is because although Halogen bulbs have good color rendering, they produce a great deal of light in the red end of the light spectrum. Manufactures try to compensate and move the color of the light produce by halogens further into the white end of the light spectrum by applying coatings that filter out the yellow colors that hover just above the red end of the light spectrum. Although somewhat effective at improving the color of the light emitted, Halogens still retain their characteristic yellow tinge, and some of the beneficial white light ends up being filtered out as well.
Further compounding the problem, the coatings used in Halogen bulbs tends to be inconsistent, leading to noticeable differences in the light quality of identical bulbs produced by the same manufacturer, particularly when place side by side. Now, the problem here is not just one of aesthetics or consistency. Although most people assume that a bulb with a higher CRI will inherently reproduce colors better, this is not the true indicator of a bulb’s effectiveness. In many applications, especially those found in the marine environment, it is very important that objects be not only well illuminated, but illuminated clearly. What this means is not that you are just throwing a lot of light on an object, but that the light you are directing on an object is revealing its aspect sharply and with good definition.
The Lighting Research Center in Troy, New York conducted tests to determine whether white light has a beneficial effect on the vision of motorists. What they found was that color rendering played less of a role in the ability to make out objects at a distance than would normally be assumed, and that the actual color of light played a larger role in determining how well an object stands out against its surroundings. To understand this seeming contradiction it is necessary to understand that in order to see an object there must be a certain luminescence difference between the object and its background, otherwise known as contrast.
The amount of contrast needed to view an object is known as the contrast detection threshold. The lower the contrast threshold the easier it is to detect an object. The tests determined that white light gives a lower luminance threshold than yellow light, particularly at sizeable off-axis angles and low light levels. What this tells us is that it is easier to see objects with white light than it is with yellow light. This explains why even with powerful Halogen beams, we seem to sometimes have difficulty with discerning the positioning and even relation of an object in comparison to its surroundings.
This is where LEDs demonstrate yet another set of benefits over the Halogens they are quickly replacing in the lighting industry. LED lamps produce light in a wholly different manner than the incandescent Halogen bulb. Instead of passing current through a filament to heat it and produce light through electrical resistance, LEDs pass current through a semi-conducting material which then emits the energy as photons or more simply, light. Now, the important thing to note here is that LEDs are very specific in the color of light they produce. Different materials when used in the construction of an LED will produce different colors. With LEDs that produce white light, an LED that produces predominantly blue light is coated with a material that forces the light to shift in wavelength towards the white end of the spectrum, resulting in an LED that produces light strongly biased towards the white end of the light spectrum with almost none in the yellow.
The results of this are threefold. First, it means that the white LED will have a better contrast threshold than the typical Halogen bulb, resulting in objects that are illuminated by the LED being easier to see and more sharply defined. Additionally, the process of producing this light in an LED is very consistent, meaning that LEDs of the same type from the same manufacturer will show a very good rate of consistency in the quality of light they produce even when placed closely together. Finally, since no coatings or filters are necessary to improve the color quality of the light produced by an LED, there is no loss of beneficial white light due to passage through a filter medium.
The implications this holds for marine applications are great. In the nighttime marine environment good visibility is at a premium. Problems with preserving night vision and still being able to safely navigate and perform activities demand that lighting be of the best quality available. To that end, LED fixtures like Larson Electronics’s LED Spreader Deck Light offer not only the ability to improve on the efficiency of the lighting used in the marine environment, but its quality as well. Even in applications where the brightest light available is less preferable than a single small fixture, the white light produced by LEDs offers to enhance vision by through improved contrast rendering of objects it illuminates.
As can be seen, there is more to the LED lighting phenomenon than just efficiency and small size. Although early LEDs tended to produce complaints of poor light quality, the last 5 years have seen improvements that not only allow LEDs to achieve a similar CRI to higher power and inefficient incandescent bulbs, but a better color quality as well. The next time you read a story about LEDs and how great their energy efficiency is, keep in mind that there is more to the story than meets the eye.