Signs of the Times - June 2014 - (Page 32)

LED Upd a te By M. Nisa Khan, Ph.D. Where Do You Put the Measuring Stick? Extended understanding of general, signage and display illumination and measurements L Dr. M. Nisa Khan is president of IEM LED Lighting Technologies. She consults in the solidstate 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 nisa.khan@iem-led.com ighting, like architecture, is a wide-reaching field. And, like architecture, it involves science and art, and perhaps other aspects of human perception and experience that are less known or understood. But, relatively speaking, the scientific part of lighting or illumination has been fairly well established at the basic level. It's best to first recognize that lighting science primarily involves three fields: * Physical science (physics); * Physiological science (the makeup of the human eye); and * Psychology (the interaction of the eye with the human brain). The latter two fields are subject to human variations and thus lack precision. However, the first - physics - is exact and has been a critical part of lighting science since humans began to understand it. Physics and its accompanying mathematics produce exact science, and thus, this aspect of lighting has no exceptions. Why physics is important By and large, current lighting-industry professionals aren't physicists or electrical engineers (EEs), although physicists and EEs have certainly contributed to lighting science. Currently, however, few, if any, work on lighting or illumination. Some experts say that physicists or EEs aren't very comfortable with the human variation of lighting science. Also, until recently, lighting designers have worked primarily with homogeneous and substantially omnidirectional, light-distribution systems - those produced by traditional lamps and, therefore, simplified understandings of light sources and measurements were sufficient. However, as LED lighting, which bears unconventional source characteristics, continues to make market strides, it becomes even more essential to establish a clear, comprehensive and rigorous treatment of illumination physics and metrology, as well as to develop engineering tools to better design and evaluate various luminaires. Fig. 1: The 3-D LID profile calculated from measured goniometric illuminance data of an LED lamp with discrete modules arranged on a 2-D plane. The LID profile is an approximate Lambertian distribution - a profile that is also expected for an LED-illuminated sign. Illumination-related measurements Although lighting physics is exact by nature, its lightingindustry understanding and implementation remain inadequate, particularly for the handling of LED-based lamps and luminaires. Lighting comprehension involves analyzing and evaluating light sources and their cast illumination. For practical reasons, the fields that involve light have separated into illumination and display (other related fields include vision, machine vision and imaging sciences). The first, illumination, typically constitutes the lighting industry. Signage, however, is a subfield within the display arena. And, although related, the different fields have developed almost independently - each focusing on slightly different physical parameters and measurement principles. But, interestingly, they all involve measuring light properties from certain sources, or illuminated objects, either directly or indirectly. Primarily, the lighting industry relies on measuring light flux or power (quantified by units of lumen) that falls onto a surface. This quantity, known as illuminance, is measured in units of lumen/square-meter or other equivalent units. Often, this measurement doesn't involve measuring any light-source property directly. Rather, it involves measuring secondary light from an illuminated surface. 32 SIGNS OF THE TIMES June 2014

Table of Contents for the Digital Edition of Signs of the Times - June 2014

Signs of the Times - June 2014
Columns & Departments
Features
ST Update
Technology Update
What Shops Need to Know about Windows XP
Vinyl Apps
Strictly Electric
LED Update
Software Update
Technology Review: X-Rite’s ColorTRUE app
Technology Review: Color-Logic’s process metallic color system
New Products
Advertising index
Editorially speaking

Signs of the Times - June 2014