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 Design Rules LED illumination from arrays isn't intuitive. L Dr. M. Nisa Khan As president of IEM LED Lighting Technologies, 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 thus far. 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 arrangement. 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
ST Update
Technology Update
Tips for Effectively Marketing Your Signs to Millenials
Vinyl Apps
Strictly Electric
LED Update
Software Update
Technology Review - The Summa F Series F2630 Flatbed Cutter/Router
Technology Review - The Durst Rhotex 180 TR
Shop Opps
Sign Museum News
New Products
Second Generation
Undertaking Monumental Tasks
The Light of Our Lives
Cool Digital Printers
Enter ST’s Vehicle Graphics Contest
Advertising Index
Editorially Speaking

Signs of the Times - June 2016