Questions About Luminaires

What about motion controlled lights?

One of the key principles of responsible lighting is that lighting should only be on when it is actually needed. Sometimes this can be accomplished with motion sensors mounted on the lights. Motion sensors are most commonly used for security lighting or in indoor applications, where animals or blowing leaves or other debris is not a problem. [The Santa Fe County Sustainable Land Development Code requires that outdoor security lighting use motion sensors.] There are some commercially available motion-controlled street lights on the market. Whether a particular street lighting application can safely use motion controlled street lighting is something that should only be evaluated by a properly trained and licensed Professional Engineer, who will then also be able to specify the appropriate detection pattern for the application. 

What about shielded lights?

A key principle of responsible lighting is that lighting should illuminate only what it is necessary to illuminate. This requires that lighting be shielded so that excess light does not “spill” or “trespass” where it is not needed. Lighting that is not properly shielded can result in glare that can obscure, for example, a pedestrian stepping out into the street at an intersection. Lighting that is unshielded can also intrude onto private property and into people’s homes. Lighting where it is not needed is wasted light. And, of course, since it costs money to produce light, wasted light is wasted money. 

The New Mexico Night Sky Protection Act requires all outdoor lighting – public and private – be shielded in such a way that no light shines upward of the horizontal. The Santa Fe Outdoor Lighting Ordinance (14-8.9) places additional requirements on outdoor lighting, including specifically a requirement no light cross residential property lines. [Regrettably, the city has not been enforcing this provision of its existing lighting code.]

If the city is interested in pursuing Dark Sky Community status better shielding than called for in the Night Sky Protection Act of the current Santa Fe City Lighting Ordinance will be needed.

Safe street lighting also requires more stringent shielding than that required by the Night Sky Protection Act or the Santa Fe City Lighting Ordinance. Glare is a particular safety hazard. The city’s lighting demonstration project did not show luminaires that were properly shielded for roadway safety. Out of respect for people in their homes, the safety of pedestrians and drivers on our city’s streets, taxpayer expenses, and the protection of our night environment, we recommend the city require luminaires with the most stringent shielding ratings, and that these luminaires be properly configured so that the shielding is effective. 

Could you explain BUG ratings in relation to street lights?

A key principle of responsible lighting is that lighting should illuminate only what it is necessary to illuminate. For street or pathway lighting, this is the street or pathway. The sky should never be illuminated. Prior to 2009, luminaires for use in path, street, or parking area lighting were rated as either full-cutoff, cutoff, semicutoff, or non-cutoff, depending on the amount of light that the luminaire allowed to be projected upward.

In 2009 the IES introduced a new and more descriptive system for describing how well a luminaire kept its light where intended. This system is known by the acronym BUG, for Backlight, Uplight, and Glare. A streetlight luminaire at the side of a road generally should not allow light to escape backward, away from the roadway, except perhaps for the purpose of illuminating an adjacent sidewalk or path. Excess light that is allowed to escape backward is called “backlight”. Similarly, a streetlight should not allow light to escape upward. Light escaping upward is called “uplight”. Finally, light that shines along the roadway (the “frontlight”) but too close to the horizontal can lead to dangerous glare. Every luminaire receives a rating, from 0 to 5, for its backlight, uplight and glare, depending on the amount of light that the luminaire allows to escape backwards, upwards, or at high angle in the “frontwards” direction. A figure showing the different backlight, uplight, and frontlight (or glare) zones can be found here. A “perfect” luminaire would have a B0-U0-G0 rating. 

Why are type II and III preferred light distribution patterns for streetlights?

When lighting is installed it needs to be configured so that the light illuminates where it is supposed to, and not where it should not. Lighting engineers have identified six different types of illumination patterns that cover most all situations faced in lighting pathways, roadways, and parking areas. These patterns imaginatively labeled types I, II, II, IV, and VS. You can download a nice “cheat-sheet” on lighting distribution types here

Briefly, the Type II and Type III distribution patterns are specifically designed to illuminate narrow (Type II) and medium (Type III) width roadways from luminaires mounted on poles at the side of the roadway. 

Does the city currently have the option to choose the amber light?

Yes. Amber street lights (color temperature less than approximately 2200 K) are commercially available. The option exists if the city chooses to take it.

Is there any difference in energy efficieny between LED bulbs of different “temperatures”? I’ve heard one of the reasons the City doesn’t want to use lower Kelvin (<2,700K) LED lamps because those require more energy.

The 2700 K – 3000 K luminaires proposed by the city’s Department of Public Works and the contractor, Dalkia, have an efficiencies of approximately 115 – 120 lumens per watt of electrical power. The 2000 K luminaires installed at the Santa Fe New Mexican printing plant have an efficiency of 125 lumens per watt. In other words, the more modern 2000 K luminaires are slightly more efficient than the lights that the Department of Public Works and Dalkia are proposing.

Would the city need to add more fixtures, i.e. light poles, to maintain the current level of safety by changing to yellow range color LED lights?

No additional fixtures would be needed. For street safety the Illuminating Engineering Society (IES) recommends roadway illumination levels that depends only on the traffic carried by the road, its posted speed limit, and the amount of pedestrian traffic. These lighting levels do not depend on the lighting color temperature. Low color temperature street lighting luminaires are as able to produce that lighting level as are high color temperature luminaires.  

Is there a cost difference between higher and lower kelvin ratings? According to Dalkia [3000-4000 K lights are] more cost effective.

“Cost effective” is a slippery term. Does it mean the cost of the luminaires? Or does it mean the cost of the luminaires plus the cost of the electrical power required to drive them over the approximately 10 year lifetime of a typical luminaire? In either event, the cost of the luminaires – at any color temperature – will depend upon the specifications the city has established for the luminaires. Despite repeated requests the Department of Public works has not made either the street lighting project requirements, or the luminaire requirements,  publicly available. Neither has the Department of Public works made available a the cost of the luminaires it is proposing for the project or what it means by “cost effective.” Without knowing what the city is requiring and what it is proposing, it is impossible to know whether the proposed luminaires are the most “cost effective” of those commercially available and suitable for use as Santa Fe City street lights, or whether any difference in “cost effectiveness” is at all significant compared to the overall cost of the project (which includes the fixtures, installation, and a long-term maintenance contract).  

Do 3000-4000 K lights have longer warranties than lower temperature lights?

No, they do not. The luminaires proposed by the Department of Public Works and the contractor Dalkia carry the same 5-year limited warranty as do, for example, the 2000 K luminaires installed at the Santa Fe New Mexican printing plant.