The Facts of Light
Have you tried navigating municipal sign codes recently? If so, you’ve probably been exasperated by how restrictive and convoluted they can be. Sign professionals know that regulations limiting allowable sizes, heights and locations of electric signs can reach extremes, rendering signs too small or inconspicuous to fulfill their core messaging and advertising functions.
Likewise, by imposing strict limits on sign luminance (brightness), a local jurisdiction substantially degrades the overall visibility and effectiveness of all illuminated signs, thus initiating a “race to the bottom” similar to that caused by the more common restrictions on sign dimensions and placements. These days, the sign industry increasingly is confronting local efforts that aim to control electric sign luminance.
SIGN LUMINANCE PRINCIPLES
When dealing with sign-brightness regulations, basic facts dispel chief misconceptions about illuminated signs. The following principles can be useful:
• Electric signs are not lighting devices – and should not be regulated as such. The core functions of an electric sign are messaging and advertising. Lighting is used strictly for the purpose of illuminating a sign’s face uniformly and at a sufficient brightness level for nighttime viewing.
• The brightness or luminance of internally illuminated signs is substantially limited by the following factors, which ensure that the majority of signs will never become sources of excessive brightness or glare: The sign industry uses standardized types, placement and spacing of internal light sources. Based on impartial testing conducted in 2013 by Underwriters Laboratories, the luminance of internally illuminated signs built today is consistent with the original guidelines for these signs developed during the 1950’s. These guidelines are described in chapter 17 (Retail Lighting) of the Lighting Handbook published by the Illuminating Engineering Society (IES). In other words, the perception that internally illuminated signs have become brighter over time is simply wrong.
The filtering effect of a sign’s plastic face on light emitted from the source (e.g., fluorescent lamps or LEDs) diffuses the light and substantially reduces its intensity. According to manufacturers’ specifications, the 0.177-in. thickness of white, acrylic plastic most commonly used for cabinet signs reduces the intensity of source lighting by 40% or more, depending on the white hue selected. Furthermore, the brightness of signs that don’t incorporate white in their color schemes is reduced to only a tiny fraction of the source-light intensity.
Environmental exposure of outdoor signs over time (e.g., solar/UV exposure, accumulation of dust/dirt and reduction in lamp brightness over time) further reduces the amount of light transmitted by a plastic-faced cabinet sign.
• Variances in signface colors, materials and thicknesses; light sources (e.g. fluorescent, LEDs or HID); aging and environmental exposure impact light transmittance of plastic signfaces. So, it’s not surprising that field measurements of existing signs aren’t a reliable basis for accurate luminance assessments. Additionally, because white transmits the maximum light of any signface color, signs without measurable white areas are unusable as references in field surveys due to the extreme, light-limiting effect of colors.
With 60 years of well-documented, consistent guidelines for internally illuminated signs, there’s no need for local jurisdictions to regulate sign brightness. In rare cases, where a specific sign may be suspected of being excessively bright, field measurements can be useful for comparing that sign’s luminance to the range specified in the IES Handbook and confirmed by modern lab tests.
However, such evaluations are seldom necessary and occur principally in response to specific complaints. Most often, the culprit in cases of regulatory overreach is simply a lack of reliable, technical information about signs – information you now have. So, when anti-sign biases come into play, be prepared.
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