Signs of the Times - April 2013 - (Page 28)
By Dr. M. Nisa Khan
As president of IEM LED Lighting Technologies, Dr. M. Nisa Khan consults in the solid-state
lighting industry and educates consumers about LED lighting. She has a bachelor’s degree
in physics and mathematics, and master’s and Ph.D. degrees in electrical engineering.
Email her at email@example.com
Understanding LED Illumination
My forthcoming book addresses science, art and the human psychology of LEDs and lighting.
Over thethe world by offering visibility have enormously
past 100 years, electric lights
hours. Electric lamps have brought benefits to personal
lives and every aspect of society – education, manufacturing, entertainment, government and all other
professions. They have also illuminated signs and
boosted sales for businesses.
Unfortunately, artificial lighting still has not reached
many parts of the world because a standard, electricpower source and distribution grid system is too costly
to build in many impoverished countries. However, LED
lamps are attracting attention as alternatives because
they’re a practical, low-power, electric-light system
that doesn’t require a grid. LED lamp technologies that
incorporate smart controls promise to revolutionize the
lighting industry by lowering energy consumption. Such
systems will also feature increased lifespan and improved
reliability compared to incandescent and fluorescent lamps.
The world could save a great deal of energy by
switching to LED lighting, because the systems are more
efficient and can run both on and off an electric grid.
To reach this goal, the LED and the traditional lighting
industries must close their long-standing gap.
So, what actually is this gap and how can relevant
industry participants close it?
The more I learned about lighting, the more the gap
became readily apparent.
I came into the lighting industry from the optoelectronics industry, which actually spawned LEDs decades
ago. Previously, I had worked as a physicist and electrical
engineer, having concentrated on optical science and
semiconductors. Like many professionals in the optoelectronics community, I innovated new optical technologies and products.
Although the optics field requires intricate work, few,
if any, of us, really understood or appreciated lighting.
This note has been echoed by many lighting authorities,
including Dr. David DiLaura who, at Lightfair 2009,
said, “…LED people don’t know lighting from licorice,
but that they will learn.”
He was right on both counts.
Lighting is an optical science. It deals with electromagnetic radiation within the visible spectrum. It’s also
art, and relevant to human psychology. Note, also,
that lighting, meaning the illumination of an area, deals
with light perceived by the human eye, which is different
from light captured by photodetector devices.
The distinction is complicated, but important to
recognize. Physical lighting quantities are only perceptions of the human eye, and these perceptions
aren’t truly analogous to other physical quantities.
28 SIGNS OF THE TIMES / APRIL 2013 / www.signweb.com
For example, optical power detected by a fabricated
sensor is radiant optical power measured in watts, but
we don’t “see” watts. What we see is luminous flux,
which we quantify with a parameter called “lumen”.
It all leads to the distinction between efficiency (the
degree to which something is done well) and efficacy
(the ability to produce the desired result). Lighting
scientists express the merit quantity “lumen/watt” as
efficacy (use “efficiency” when both quantities before and
after conversion can be expressed by the same unit).
Luminous flux is generated from radiant power
emitted by a lightsource, and it usually scales with the
source power – but not always and not always the same
way. Radiant power converts to what we perceive by
weighting it with the human-eye sensitivity function at
each wavelength in the visible spectrum and then summarizing them. However, applying such a conversion
method doesn’t always lead to what we see in different
environmental conditions, because our perception is
also affected by light levels, contrast, color and other
physical parameters, as well as subjective parameters
and each person’s vision adaptability. Nevertheless,
such conversion methods remain the best approaches
we have to quantify lighting.
Most fascinating is the aspect of lighting that’s beyond
traditional optics and other hard sciences and engineering.
As one explores this facet, two things become clear:
a) Lighting is a field in its own right, and many
lighting, vision and color scientists have served the
field as notable contributors.
b) LED lighting, because of the intricacies of optoelectronic science and manufacturing technologies,
is more complicated than most LED and lighting
scientists and engineers realize. LEDs are a different kind of light source, and understanding
them requires knowledge of the fundamentals
of lighting sciences and mathematics.
My forthcoming book, “Understanding LED Illumination,” will be released in August. Its seven chapters
offer the following features and benefits:
1) The basic notion of emphasizing the lighting aspects
of LED lamps. The solid-state lighting (SSL) community
should recognize that LED lamps must provide more
than a glow and higher luminous efficacy. The quality
of the glow must also be improved and be effective.
2) The basics of junction diode, and the intricacies of
compound-semiconductor optoelectronic properties,
including thermal, electrical, optical and mechanical
aspects. The book provides lighting-industry professionals with a compact source from which to
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