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There is more to lighting than meets the eye

Les Kacev is passionate about lighting education, measurement and the quality of light. He has run seminars, workshops and webinars for utilities, associations, universities, LED manufacturers, vendors, distributors, and conferences. A few examples follow

The human eye is truly our window to the world. Not only does it contain rods and cones which stimulate our vision, but it has recently been discovered that the eye contains a variety of intrinsically photosensitive retinal ganglion cells known as ipRGC which are involved in non-visual functions. Light and light quality play an immensely important role in stimulation of ipRGCs and in so doing determine our mood, sleep patterns, productivity, health and  general wellbeing. Light exposure plays an important part in our mental health.

Not only does light [natural and artificial] affect humans, but its impact on fauna and flora is only now being appreciated. Its influence on mammals, birds, bats, insects, fish and plant life has opened up a new branch of science.

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Everyone knows what a 60 watt incandescent A19 light bulb is. No matter who the manufacturer, they all have approximately the same intensity, the same color in degrees Kelvin, the same color rendering ability and the same light distribution pattern [beam width or angle of dispersion – 360 degrees].  Their spectral power distributions are identical and they all act as black body radiators.

However, the same cannot be said for solid state LED lighting. A 10 watt LED A19 light bulb can vary significantly in intensity, is offered in a variety of color temperatures and monochromatic colors, can range dramatically in color rendering and can be found in many dispersion patterns. Their spectral power distributions can differ significantly and they may lie on, above or below the black body locus.

The big push for LEDs is because of energy savings. The criterion for efficiency is lumens per watt. Many mandated regulations call for a specified wattage per square foot and/or foot candle rating in the area being lit. On occasion, a minimum color rendering [CRI] and a maximum correlated color temperature [CCT] is specified.  Because of the variety of parameters that serve to characterize the “light quality” of LED sources, these specifications are inadequate and can lead to less than optimal lighting installations.

Information contained on the packages of LED lamps and luminaires are insufficient for buyers to make an informed purchasing decision. Even those that comply with the “Lighting Facts” labeling requirements fall short for practical purposes. LM79 reports are usually too complicated for the average consumer or lighting professional to comprehend. Often manufacturers change designs so LM79 reports may not be accurate.

There are no shortcuts. There is no single number that defines light quality when it comes to solid state, LED lighting. It is not rocket science, but it is fairly technical, requires some education, and a tool to measure the defining parameters.

Lux meters are no longer adequate to determine light quality. What is needed is a spectrometer. There are many different types of spectrometers. What we are referencing is an apparatus that measures the radiated characteristics of light in the visible portion of the electromagnetic spectrum from around 380 to 780 nanometers [nm].  The ideal tool is the Lighting Passport [LP] smart phone/tablet spectrometer.  LP is an accurate device that uses the computational power and graphic display of an iPhone/iPad or  Android smart phone or tablet. It has a comprehensive and user friendly range of “applications” and related PC software.

The Lighting Passport spectrometer is an indispensable device for all lighting professionals. This includes manufacturers, vendors, distributors, design engineers, quality controllers, sales engineers/staff, architects, lighting designers/specifiers, retail lighting establishments, contractors, installers, electricians, property developers/managers, hospital maintenance staff and more.

The prime defining characteristics for quality of light are:

  • Spectral Power Distribution [SPD]
  • Correlated Color Temperature [CCT]
  • Color Rendering Index [CRI] – but not just Ra, but R1 through R15
  • Proximity to the Planckian Locus [in one of the CIE Chromaticity Diagrams]
  • Illuminance in lux or foot candles.

Secondary defining characteristics are:

  • Peak wavelength
  • Dominant wavelength
  • Purity
  • Scotopic/Photopic Ratio [S/P Ratio]
  • ANSI C78.377-2008 [representing 8 standard tints in LED lighting based on CCT]
  • IEC Standard Deviation of Color Matching  [SDCM with MacAdam Ellipses]
  • Photosynthetic Photon Flux Density [PPFD and YPPF] for horticulture

Lighting Passport spectrometer allows you to measure all of these in seconds, save them if necessary and share them with colleagues via email or WiFi.

NOTE: The lighting Passport spectrometer can be used to measure any light source, not just LEDs.