INFORMATION

INDUCTION LIGHTING

Magnetic induction lamps are basically fluorescent lamps with electromagnets wrapped around a part of the tube instead of the traditional electrodes found in normal fluorescent lamps. In induction lamps the lamp ballast takes the incoming mains AC voltage [or DC voltage in the case of 12V and 24V ballasts] and rectifies it to DC. Solid state circuitry then converts this DC current to a very high frequency output which is between 210-270KHz for low frequency and 2.5-6.5 MHz for high frequency fittings, depending on lamp design.


This high frequency is fed into the coil wrapped around the ferrite core of the inductor. This high frequency creates a strong magnet field around the inductor and thus into the lamps glass tube which it surrounds. The magnetic field excites the mercury atoms inside the tube and causes them to emit UV light in the sealed gas tube, and just as in a fluorescent tube, the UV light is up-converted to visible light by the phosphor coating on the inside of the tube. The system can be considered as a type of transformer where the inductor is the primary coil while the mercury atoms within the envelope/tube form a single-turn secondary coil.

PUPIL LUMENS (Plm)

Describing light as "lumen output" and measuring it as "foot candles" on a work plane have been the traditional ways of describing and defining how much light is required to perform a variety of tasks. However, that is being re-examined based on results of studies on visual performance and the psychological impacts of lighting. Additionally, the "color rendering index" (CRI) and "color temperature" (K) describe the quality of the light. As lighting technology evolves into various types and colors, simply measuring the lumen output levels proves not to be fully adequate when predicting how well people can see. An excellent example of this is the high-sodium lamp which produces many lumens, but mostly two colors (yellow and gray) producing a colour temperature rating of around 2000 Kelvins (K). The ability to make out details-beyond shapes of objects-is lost under this light source. Different light sources produce light in different spectral ranges with human vision being best served with the whiter colour temperatures in the range of 3000-6000K.
Vision itself is affected by many factors, from light intensity, distribution, color, and contrast, as well as reflections, glare, air quality, motion of subjects and viewers, and more. Our eyes use different parts to see in bright light and low light conditions. The eye contains cones and rods which were thought to work in opposite conditions. Cones provide color vision and fine detail (photopic) in bright light and rods take over in dim light (scotopic). In bright light our pupils contract allowing more detail to be perceived, while depth of field and perceived brightness also increase. In low light our eyes dilate to allow more light in.
Light meters and recommended light levels for tasks have traditionally been calibrated for daytime viewing, and general interior lighting, based on the photopic response. However, studies are indicating that the scotopic vision is more involved in interior lighting than previously thought, and affects pupil size. These studies have led to the formulation of the photopic/scotopic (P/S) ratio.
The P/S ratio is a correction factor which, when applied to the lumen output of various light sources, expresses the effective lumens the eye will perceive for vision based on the size of the pupil and its effect on vision (see Table 1). Some lamps, like high-pressure sodium, lose most of their output using this method, while others like high-quality fluorescent lamps, metal halide and induction lamps gain substantially.

Light Source

Conventional
lumens per watt

Correction
Factor
(P/S ratio)

Pupil Lumens
per watt

4,000K Induction

80

1.96

157

5,000K T5 fluorescent

104

1.83

190

4,100K T8 fluorescent

90

1.62

145

Metal halide

75

1.49

112

2,900K warm white fluorescent

65

0.98

64

Daylight fluorescent

55

1.72

95

High-pressure sodium

90

0.57

51

Standard incandescent

18

1.26

23

Table 1