Induction Lighting is a proven lighting technology that has been around for over 100 years. Due to recent advancements in Electronic Ballast/Generator technology, it has more recently become a viable option for the commercial and municipal markets. Induction Lighting has been utilized extensively for street lighting applications in Asia, Australia, and Europe, however with the recent initiatives to “GO GREEN”, induction lighting technology is now emerging as the best choice for energy efficient lighting in North America.
An Induction Lamp is similar to a fluorescent lamp in that mercury in a gas fill inside the bulb is excited, emitting UV radiation that in turn is converted into visible white light by the phosphor coating on the bulb. Fluorescent lamps, however, use electrodes inside the bulb to strike the arc and initiate the flow of current – each the arc is struck, the electrodes degrade a little, eventually causing the lamp to flicker and then fail.
Induction Lamps differ in that they do not use internal electrodes, but use a high-frequency generator with a power coupler. The generator produces a radio frequency magnetic field to excite the gas fill.
With no electrodes, the lamp lasts longer – in fact, up to 100,000 hours, with the lamp producing 70% of its original light output at 60,000 hours.
In other words, their rated life is 5-7 times longer than metal halide (7,500 to 20,000 hours at 10 hours/start) and about seven times longer than T12HO fluorescent (at 10 hours/start) .
Many people, who see induction lights, comment on how bright they appear and on what they feel is a higher quality of light being emitted from the fixtures. However, when individuals compare a induction light to a conventional lamp with a light meter, the Induction lamp is generally measured as producing less light than the conventional lamp. This has led some people to question the installation of these fixtures – even though they use 50% less energy – as they expect that the areas lit by them will not be bright enough when compared to conventional lighting. All this, even though their eyes are telling them they are the same if not brighter.
The issue is not with the induction lights and their ability to produce acceptable light. Today’s standards for light meters are calibrated using the 1951 CIE Color Space Standards. They have not evolved with advancing technology in the lighting arena. This standard used to set the sensitivity curve for light meters does not take into account the contribution of Scotopic vision (night vision) to the sensitivity of the eye. Scientific studies have shown the eye is more sensitive to blue wavelengths than the measurement curve of the light meter. Blue light, acting on human night vision (scotopic vision) is largely responsible for “visual acuity” or sharpness of vision. Simply put, light meters and the 1951 standards by which they measure light are wrong. Consumers are therefore paying for products with yesterday’s lighting quality while not taking advantage of today’s products, such as induction lighting that offer reduced costs and a better quality of light.
The human retina contains@ 125million rod cells and @ 6 million cone cells. These respond to different frequencies (colors/ wavelengths) of light in different ways. Cone cells are adapted to detect colors and function well in bright light, while rods cell are more sensitive but do not detect color well as they are adapted to low light.
Photopic Vision is the scientific term for human color vision under normal conditions during the day (i.e. human perception of red, green and blue that the brain integrates to form full color images of the world around us.)
Scotopic Vision is the scientific term for human visual perception in low light (night vision).
Mesopic Vision is the scientific term for the combination between Photopic and Scotopic vision taking into account the total sensitivity of the rod cells in the eye for the blue range, with the color perception of the cone cells.
The ratio of Photopic light vs. Scotopic light in a lamp is called the S/P ratio. This ratio determines the apparent visual brightness of a light source. This is why the 200w lamp will appear as bright or brighter to the human eye than a sodium vapor or metal halide of twice the wattage.
How does it work?
Light is measured in Lumens (Lux or foot Candles). The S/P ratio of a lamp is important as it provides a number that can be used to multiply the output reading of a lamp using a 1951 standard conventional meter to determine how much light, which is useful to the human eye, a lamp produces. These are known as Visually Effective Lumens (VEL).
Using a conventional light meter or spectrometer, the light is measured to determine the photopic vision sensitivity curve. Using the same light source with a light meter calibrated to the scotopic, the scotopic sensitivity curve is determined. The resulting readings form an S/P ratio that can be expressed as a Single number.
The chart below gives a comparison of MHT Induction Lamps S/P ratio compared to other common industrial lamps. These figures are based on Data received from Francis Rubenstein of Berkley Labs.