INDUCTION SP RATIO
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.
Here’s how it actually works:
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.
S/P Ratio Example
Metal Halide – 400 watt has manufacturers rating of 56.9 lumens per watt. This results in 400×56.9=22,760 lumens x1.49 (S/P ratio) =33,912 Visually Effective Lumens.
Induction – 200 watt has a manufacturers rating of 80 lumens per watt. This results in 200×80=16,000 lumens x2.25 (S/P ratio) =36,000 Visually Effective Lumens.
The new- patented Induction Lighting technology is essentially a florescent lamp without electrodes. With the absence of electrodes and filaments the lamp relies on the fundamental principles of gas discharge and electromagnetic induction to produce light. The result is a lamp with an unmatched life span. The lamp and ballast system has an unparalleled 5 year guaranteed warranty. In normal terms this is a 100,000-hour life span or 25 years when operating 8 hours per day.
The Lumen Maintenance curve depicts the actual lifetime of the Visually Effective Lumens (light) as compared to other lighting scenarios. The induction lamp outlasts the competition whether it is HID (MH of HPS) or the newer T5 & T8 anywhere from 3-5 times longer. All the time, while maintaining an industry leading lumen output.
Using a conventional light meter or spectrometer, the light is measured to determine the photo topic 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.