Signs of the Times - June 2016 - (Page 32)
LED Upd a te
By M. Nisa Khan, Ph.D.
Challenges in Setting LED
Sign Illumination Optimization
LED illumination from arrays isn't intuitive.
Dr. M. Nisa Khan
As president of IEM LED
Dr. 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
ED sign manufacturers continue
to seek straightforward design rules
that would allow them to obtain
an optimally illuminated sign that
satisfies their customers in terms
of color and brightness. Because
such rules exist for neon- or fluorescent-illuminated channel letter
and cabinet signs (see Randy Wright's
rule of thumb for tubular lamps in
ST's October and December 2014
issues, pages 38 and 30), many -
not all - signmakers believe a rule
of thumb also exists for arranging
LED modules to optimally illuminate signs. This is not the case
Because of their different shapes
and bends, LED channel letters
require the most difficult lighting
configuration. However, the regular
arrangement of LED modules is
not the sole factor that determines
illumination uniformity, as evidenced in LED-illuminated cabinet
signs that often show uneven illumination despite the rectangular
shape that provides a predictable
Signmakers who've noticed that
no straightforward rule exists for
uniformly and optimally illuminating rectangular cabinet signs
with LED modules often deliberate
the LED light-dispersion dilemma.
They ask what factor determines the
proper gap between LED modules.
In addition, what dictates the proper
clearance, i.e., the distance between
the LED modules and the sign face?
These are seemingly minor but
important questions. If lamp-to-face
clearance is too small, the sign
face may have too much glare.
Worse, pixelation (light emanating
from each individual LED lamp)
could be visible, which means the
sign requires a sufficiently opaque
sign face. If the gap is too large, the
sign center-zone brightness may be
acceptable, but brightness near the
sign edges could be insufficient. Do
such circumstances seem familiar?
Simulating LED illumination
of cabinet signs
LED illumination from arrays isn't
intuitive. Unfortunately, almost
every lamp buyer believes LED
lamp illumination corresponds to
traditional incandescent and fluorescent lamp illumination. Heightening this belief is lamp manufacturers'
practice of mimicking traditional
lamp design formats. Such manifestations further affect users'
beliefs of lighting similarity.
The worldwide absence of illumination standards presents challenges for both manufacturers and
users when comparing values for
an appropriate set of characteristic
parameters from different lamps.
The lighting industry's currently
specified parameters - such as total
lumen power, luminous efficacy
and beam angles - aren't sufficient
to comprehensively describe illumination. In the case of illuminating
channel letters and cabinet signs,
using such parameters hasn't
helped anyone create a guide for
optimal illumination of LED signs.
The best way to visualize how
LED lamps illuminate signs is to
calculate the illumination pattern
from an array of LED modules at
different distances - clearances
- from the source plane. As an
example, using the Zemax soft-
Fig. 1: Zemax simulation of 16 LEDs
2mm from the source plane. Peak
illuminance: 7.53 million lumen/m2;
total power: 4.79 thousand lumens.
Fig. 2: Zemax simulation of 16 LEDs
5mm from the source plane. Peak
illuminance: 1.81 million lumen/m2;
total power: 3.19 thousand lumens.
Fig. 3: Zemax simulation of 16 LEDs
15mm from the source plane. Peak
illuminance: 0.715 million lumen/m2;
total power: 1.59 thousand lumens.
32 SIGNS OF THE TIMES June 2016
Table of Contents for the Digital Edition of Signs of the Times - June 2016
Signs of the Times - June 2016
Columns & Departments
Tips for Effectively Marketing Your Signs to Millenials
Technology Review - The Summa F Series F2630 Flatbed Cutter/Router
Technology Review - The Durst Rhotex 180 TR
Sign Museum News
Undertaking Monumental Tasks
The Light of Our Lives
Cool Digital Printers
Enter ST’s Vehicle Graphics Contest
Signs of the Times - June 2016