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

Lig hti n g T e c hn i ques By Marcus Thielen Marcus Thielen is a physicist and lighting-industry consultant from Duisburg, Germany. LED Radiation Characteristics Why lighting signs evenly can rarely be calculated A s an expert witness in court, I've most frequently been asked: "Is the sign lit evenly"? "Evenly" is subjective, but science and court cases are more objective, so measurement values become the judge. regarded as "pointsources" in the sense of radiation physics, which simplifies the math. A clear (NOT frosted glass) incandescent lamp can also be regarded as "pointsource." At double the distance from the source, the incandescent has an illumination intensity reduced to ΒΌ. (Per radiation physics, the surface the light Early in lighting technology (the 1930s), research found a surface to be lit subjectively evenly "if the eye adapted to artificial light does not recognize luminous density variations larger than 1:1.5. If the variation is greater than 1:2, the illumination will be considered boring uneven" (citation from OSRAM research reports, 1931). Such results remain valid today (Fig. 1). Ideally, to light a surface uniformly, the lightsource itself should have a large, uniformly lit surface. However, LED dimensions are significantly smaller than typical sign faces. The LEDs are more "points" than surfaces. Thus, LEDs can be Fig. 2: The schematic principle of the square-distance law of radiation and a spherical coordinate system for light measurements Fig. 1: An unevenly lit surface. In a shopwindow, LED showcase, beside the color difference, the luminous density varies 1:1.97. 32 SIGNS OF THE TIMES May 2014 Fig. 3: An example of the angular-intensity measurement, in two perpendicular planes of orientation, for an optimized lightbulb (OSRAM, 1931)

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

Signs of the Times - May 2014
Columns & Departments
St Update
Technology Update
Typography Foe Wide-Format Design
Vinyl Apps
Strictly Commercial
Lighting Techniques
The Moving Message
Technology Review: The Mutoh ValueJet 1617H printer
Technology Review: CorelDRAW Graphics Suite X7
Design Matters
New Products
Advertising Index
Editorially Speaking

Signs of the Times - May 2014