The American Heritage® Dictionary of the English Language defines L.E.D. as: ”A semiconductor diode that converts applied voltage to light and is used in digital displays.”
Other sources define it as a “light-emitting diode,” meaning a diode that emits light when current passes through it. Regardless of technical definitions, LED Technology is phenomenal and is frequently found in your daily routine. In traffic signals, outdoor electronic message displays, indoor programmable displays, fixed image displays, lighting tubes, vehicle backup lights and in countless other applications, LEDs are rapidly replacing neon, incandescent and fluorescent light sources.
LEDs are constructed differently than traditional light bulbs because they are channeling all of their energy into producing light rather than heat. LEDs are durable, are normally encased in a high strength cover, do not contain any filaments, moving parts, or glass components of any kind, thereby making them nearly unbreakable.
The Primary advantages of using LEDs instead of conventional lighting technologies are:
Throughout the country, more and more municipalities are enacting sign ordinances to control the size, place, and manner of on-premise signs, but their light output, as well. On-premise signs identify businesses or services performed at the location of the sign itself, and although they produce a very small portion of the overall light in any given environment, they do require some lighting at night to becomce visible. USSC has long contended that these types of signs differ from standard outdoor lighting fixtures and devices in that their light is not intended to provide task or ground illumination, but rather to enable them to convey their specific message at night. Nonetheless, it is likely that before long, virtually every municipality that adopts a new sign code or revises a current one, will attempt to mandate illumination levels as yet another restriction for signs. It is important to understand, as well, that these sign lighting controls will apply not only to internally illuminated signs and letters, but to externally illuminated signs as well, in terms of restriction on the overall amount of light either projected from the sign or reflected from its face.
To help cope with this increased regulatory burden on sign producers, USSC will soon distribute to its members a definitive 28 page guideline book entitled.
The purpose of this latest USSC publication is to:
Overview Purpose of On-Premise Sign Illumination Types of On-Premise Sign Illumination and their Impact on Driver Safety Since 2004, The United States Sign Council (USSC), through its research entity The United States Sign Council Foundation (USSCF), has funded extensive research into on-premise sign illumination. The four distinct USSCF university level studies published to date are now widely regarded as a definitive basis for a full understanding of the unique environmental and safety factors involved in both the design and use of on-premise sign illumination in the nighttime environment. These USSCF sign lighting studies, conducted by the Thomas D. Larson Pennsylvania Transportation Institute at the Pennsylvania
On-premise signs serve a variety of communication, advertising, and wayfinding functions, principal among which is the place marking of the location or building on which they are installed. Simply stated, onpremise signs tell people where something is located in the landscape In high speed or congested traffic environments particularly, this placemarking (or situational wayfinding) function of on-premise signs can be a critical component in providing motorists and viewers in general with a precise and unequivocal awareness of the location of places and points of interest in the environment through which they are traveling.
Although significant advances have been made with in-vehicle navigation technology through GPS and other systems, it is still the on-premise sign alone that provides motorists’ situational awareness with absolute precision, certainty, and reliability, while requiring only the normal visual scan of roadside cues familiar to every motorist.
This critical function of the on-premise sign, of course, must be met not only in daylight, but after dark as well. It is for this reason that on premise signs are illuminated. On-premise signs require illumination that is as effective and as efficient as possible, because artificial light, even when optimized, is unable to provide equal visibility and legibility attainable under ordinary daylight conditions. Yet the need for the roadside information transmitted by on-premise signs increases substantially in the more challenging nighttime driving environment.
Types of On-Premise Sign Illumination and their Impact on Driver Safety
Signs are visible in the daytime because sunlight reflects from the face of the sign. At night, for signs to be bright enough to be detected and read, they must be artificially illuminated. This can be done either internally or externally. As the name suggests, internally illuminated signs, are lit from the inside, with light sources mounted within the sign cabinet itself back-projecting light onto the sign face.
This is mainly accomplished using fluorescent bulbs, neon tubes, or light emitting diodes (LEDS) Externally illuminated signs are litfrom outside the sign, usually by flood lamps mounted above or below the sign face.
Research has shown conclusively that internally illuminated onpremise signs are read from a much greater distance than externally illuminated signs. This was first demonstrated on a test track where 40 to 60 percent longer reading distances were found with internally illuminated signs. This improvement was found even though the lights for the externally illuminated signs were bright, new, and carefully placed and aimed. Because many externally illuminated signs in the real world are under-lit, poorly aimed, and dirty, a second study on real roads was conducted. The result was that when externally illuminated signs in the real world were switched to identical signs that used internal illumination, on average people read the internally illuminated signs 70 percent further away and in some cases at more than twice the distance.
There are two basic sign lighting concepts. The first relates to the brightness of the sign itself. In this sense, brightness is created either by light that is back projected onto the face of an internally illuminated sign or light that shines on the front face of an externally illuminated sign. In light measurement terms, this idea of brightness is called luminance. Because luminance describes a characteristic of the sign, it is not affected by distance. In other words, it doesn’t matter if an observer is two inches from a sign or a mile away (or is not there at all), the sign has the same luminance, just as it has the same color and size.
Illuminance: The second sign lighting concept addresses the question of how much of the light that shines from a sign face reaches some point in the distance. This is technically referred to as illuminance, which is simply a projection of the light from the sign into surrounding space, such as light cast by a reading lamp on a book, or a street light on the road surface. Illuminance diminishes rapidly with distance, and this reduction in light is measurable at any point from the sign at a rate equal to the square of the distance from the sign. Luminance and illuminance are related to each other through reflection. When a beam of light (illuminance) hits an object the object lights up (luminance). Depending on the reflectance of that object, it appears more or less bright. A black object has low reflectance and so it absorbs more light than it reflects, and it appears dark. The absorbed light is converted into heat which explains why a black car sitting in the sun is hotter than a white car right next to it. Higher reflectance is also why the white car is brighter and in general easier to see.
In summary, sign luminance is simply a measure of the light at the surface of the sign while sign illuminance is a measure of the light cast by the sign into surrounding space.
The importance of distinguishing between sign luminance and illuminance. A well designed sign with the proper amount of luminance gives approaching motorists sufficient Viewer Reaction Time to allow for a comfortable period of detection, legibility, and driving maneuver in response to the sign at its particular location. On the other hand, even otherwise well designed signs can have a pronounced negative effect on VRT if they have insufficient luminance.
Research has shown that if a sign is too dim, it will be difficult to find because it will not differ enough in brightness from its surroundings; this is known as external contast. A dim sign will also not be readable because there is not enough difference between the sign copy and the sign face background; this is called the sign’s internal contrast.
Alternatively, research also confirms that if the luminance of an internally illuminated sign is increased to abnormally high levels, although the sign becomes brighter and therefore more detectable, no advantage in legibility is gained, and, in fact, some legibility may be lost. This, of course, underscores the need to keep sign luminance within ranges that will optimize legibility.
Illuminance, or the amount of light that shines from a light source onto other objects, has only an indirect relevance to on-premise signs. Since on-premise signs are not designed to cast light on other objects or spaces, their illuminance only becomes relevant in terms of its possible relationship to an environmental concept called light trespass.
The (IESNA) describes light trespass as “light that strays from the intended purpose and becomes an annoyance, a nuisance, or a detriment to visual performance.” It is light that shines where it is not wanted. Light trespass can result in if it is shining in someone’s eyes, or it can simply and annoyingly light up an area it is not supposed to, like when a street light or a car’s headlamps shine into a bedroom window.
Because internally illuminated signs have low initial light levels that fall off rapidly with distance, these signs have virtually no significant light trespass. It is mainly a problem with badly aimed lighting of externally illuminated signs, in particular when spot or flood lights spill over the edges of the sign or are so poorly aimed that they miss the sign altogether.
Nonetheless, in addition to their other provisions, sign codes may address the issue of light trespass by requiring that the illuminance of signs at the property lines be restricted to a specific level.
PowerSmart, the PowerSmart logo, and the Millennium Visual Systems logo are trademarks of Millennium Enterprises LLC.
Copyright 2010 Millennium Enterprises LLC, All rights reserved.
