Besides minor modifications and the addition of the "full cut-off" category (figure 1) in 1990, the same classification for outdoor luminaires has been employed since 1963.
Since municipalities wanted, from manufacturers, a more precise evaluation of their IES files in order to be able to choose the right luminaire for a project, a revision of classification became necessary. With the influx of complaints coming from their residents, cities and municipalities were confronted by three problematic situations.
1. Light trespassing represents the highest quantity of complaints; unwanted light on your property, particularly inside your house. We often encounter this problem when a photometric study is requested by consultants or representatives of a municipality and a house-side deflector is not specified even though the dwelling is near a road or a parking lot.
A deflector is used to redirect, eliminate, or reduce, the light that is cast in the direction of a home. In the case of intrusive light, we want to bloc the light that shines into bedrooms.
Medical studies have shown that our internal biological systems need a true nocturnal environment to generate the maximum amount of melatonin. This hormone is generated from serotonin and is used to trigger the sleep cycle that helps the body recuperate and regenerate after a hard day of staying awake.
The current classification system was not enough since it only addressed the total light cast towards the back of the luminaire.
2. The second problem was the glare experienced by motorists on the road. This phenomenon is caused by luminaires that emit a lot of light at near right angles (close to paralleling the horizon). This is a major issue since manufacturers are asked to create luminaires that can be spaced out at large distances forcing them to have optical systems (reflectors or refractors) that cast at those elevated angles. Depending on the environment, this problem causes a glare effect that could lead to, depending on the angle, momentary blinding effects suffered motorists. This blinding effect is more than problematic. Consider people crossing the road while the motorist is under the effect of this glare.
3. Finally, the issue that makes all the news; light pollution, defined as the quantity of light a luminaire shines towards the sky added to the light that is reflected from roadways, streets and pavement. The roadway reflection issue, unfortunately, can't be solved by a new classification.
If we want to measure the total contribution to light pollution, we have to make a photometric calculation that includes the direct output of the luminaire towards the sky and the reflected output. Astronomers, who noticed stars disappearing from the sky, brought light pollution to our attention first. We're speaking of disappearing stars because that is the phenomenon observed in major cities where an observer looking at the sky can see only a few dozen stars compared to someone in the country who, while looking up, can see thousands. But this problem doesn't only concern astronomers, studying stars has noticeably enriched human knowledge and a considerable amount of study remains to be done in this vast field. Who knows what more we can learn by looking at our stars, and, all it takes to keep them in our night sky are a better luminaires.
To address those three problematic issues, the IESNA (Illuminating Engineering Society of North America) has revised the technical memo TM15-07(revised) to include more detailed aspects on the light emitted by a luminaire in different zones.
From now on, we no longer simply consider the light cast towards the back of the luminaire. The previous back zone has been expanded and redefined (figure 2) into four.
BL = back low
BM = back medium
BH = back high
BVH = back very high
The same thing applies to the front zone (figure 3):
FL = front low
FM = front medium
FH = front high
FVH = front very high
And for uplight we went from only one zone to two (figure 4):
UL = Uplight low
UH = Uplight high
Many documents (recommended practices) using the new TM15-07(revised) classification will soon be produced, including the MLO "Model Lighting Ordinance". The MLO will help regulate all types of lighting projects with the exception of street and highway lighting, which is already regulated by cities; the 3 afore mentioned problematic issues stem largely from private lighting. The MLO document will help eliminate certain types of complaints, for example: light trespass form a commercial parking lots that uses 1000w metal halide luminaires installed on the limits of residential properties. The MLO includes other definitions as well: mathematical formulas based on performance will be added to the already existing prescriptive methods. Useful when one does not want to do photometric calculations.
The document will first define the types of environmental lighting zones (Z0, Z1, Z2, Z3, Z4). For example a provincial or state park would be Z0 and a large metropolis would be classified as Z4.
Different restrictions will be defined by different environmental zones. To simplify everything, only three letters need to be remembered; BUG: B for Backlight, U for Uplight and G for Glare. Each letter will include different zone specifications. For certain cities, the BUG rating to meet will be 2 and for others it might be 4. This will make it possible to know, before installation, that a luminaire conforms to specific codes and regulations set in place ensure a better quality of lighting for specific environments.
There will also be, for each environmental zone, a defined limit for backlighting "B". The purpose here is to define the different limits in relation to the distance that separates luminaires from houses.
To wrap up, TM15-07 is a reform of the classification of outdoor luminaires that, in conjunction with the MLO document, will permit you to select the absolute best and most appropriate luminaires for your projects.
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