Lighting a Building Exterior: Secure, Efficient & Well Designed
Published October 2013 by Energy EfficiencyExterior LightingLight PollutionLighting DesignNight Lighting
POST UPDATED JUNE 2016
There are many things to consider when lighting the inside of your facility, but your nighttime exterior lights should be an equal concern. Do you have enough light for people to safely navigate around your walkways and parking areas at night? Are you positive you aren’t over-lighting, wasting energy and polluting the night sky with extra light? There is a fine line to stride when it comes to designing the best exterior lighting system for your building. When you mindfully design an exterior lighting system, these components come into balance and it is relatively easy to achieve a night time environment that saves energy, offers quality light and does not waste energy or spill light into unwanted areas.
AVOIDING LIGHT POLLUTION
One modern lighting concern when it comes to exterior lighting applications is light pollution. Light pollution factors include Glare, Light Trespass and Reflected Light. When a lighting designer chooses the correct fixtures for each area of your outdoor lighting, with the correct amount of light specified, these three factors are negated. Here’s an easy definition of each:
Glare is a visual sensation caused by excessive and uncontrolled brightness. It can be disabling or simply uncomfortable. It is subjective, and sensitivity to glare can vary widely. Source
Light trespass occurs when spill light is cast where it is not wanted. Light trespass is somewhat subjective because it is difficult to define when, where, and how much light is unwanted. An example of light trespass is when spill light from a streetlight or floodlight enters a window and illuminates an indoor area. Proper aiming of the floodlight and shielding would significantly reduce the light trespass. Source
Reflected light happens where extra light is cast off of surfaces and directed into areas where it is not required, but it can also be light that reflects off of surfaces you intend to light, such as sidewalks and parking lots. Some amount of reflected light is unavoidable, but to cut down on reflected light and “Sky Glow” be sure that light levels are appropriate and that areas are not over-lit.
NIGHT TIME SAFETY CONCERNS
Safety is a big reason for lighting your building exterior at night. Of course, people need to be able to travel on foot or by vehicles safely around your facility at night, but this can also include dusky hours early or late in the day in areas that are particularly shadowy. Walkways, parking areas, loading docks and entry spaces should all be lit for the safety of people working, walking or driving in these areas.
Many buildings also have wall fixtures on the sides of buildings wash light over and around windows. These lights reduce shadowy areas and increase a feeling of security, while giving light to areas where security cameras may be pointed. These safety measures lead us to the next point: Recommended Light Levels. Recommended levels are also primarily based on safety and security functions and can help reduce crime and instances of vandalism.
LIGHT LEVELS FOR EXTERIOR LIGHTING APPLICATIONS
IESNA (Illuminating Engineering Society of North America) recommended light levels for most exterior lighting applications ranges from a minimum .2 foot candles in low traffic outdoor parking areas, up to 2 foot candles for buildings and large open areas. A minimum of 5 foot candles is recommended in pedestrian areas and entrances. Keep in mind that these figures are recommendations, and that state and local standards can be found in local building codes, which should be consulted when designing a lighting system. The goal with these recommended levels is to use as much light as needed without over-lighting which results in wasted energy and light pollution.
LIGHT QUALITY FOR EXTERIOR LIGHTING APPLICATIONS
While light level recommendations should be carefully regarded, the quality of light you need for exterior applications should not be overlooked. What does “Light Quality” mean exactly? A quick explanation compares two types of light that are probably familiar to you. First, imagine the common orange light (high pressure sodium technology) that you have seen in parking lots and street lights for many years. This orange colored light seemingly washes out the ability to distinctly identify other colors; making objects and people under this type of light seem grayish. Now think of places you may have recently been with fluorescent or LED lighting, maybe a parking ramp, and compare how the colors of the cars were more distinct – you could likely identify navy blue or dark green from black vehicles. You probably felt like the light was brighter in the fluorescent or LED lit environment.
In fact, it’s entirely possible that these two scenarios could be lit with exactly the same amount of foot candles and there’s nearly a 100% chance that the high pressure sodium (orange) was using multiple times more energy than the fluorescent or LED lights. The difference is light quality, the CRI (Color Rendering Index) of the lamps used in the fixtures. The high pressure sodium lighting has a very low CRI, but can use hundreds of watts of energy. Fluorescent and LED lighting both have higher CRI’s than High Pressure Sodium, and the most up-to-date iterations are energy-efficient. It’s also important to note that with LED technology, the spread of light has been precisely engineered to reduce areas of high and low light to give a very even area of light coverage. The conclusion here is that “higher watts” does not necessarily equal more light or better light quality.
REDUCING MAINTENANCE COSTS WITH MODERN LIGHTING TECHNOLOGY
By renovating your lighting technology, you save energy and thusly, you save money. However, another important retrofitting savings factor for outdoor (or any difficult to reach area) is the savings achieved through reduction in maintenance costs. There are three ways you can recognize maintenance savings:
- By streamlining technology and having just 2 or 3 different lighting technologies (bulbs and ballasts) throughout your facility, you do not need to keep as much replacement material in stock.
- Your new lighting technology for exterior applications, LED especially, will have a long lamp life that reduces the amount of maintenance hours required to upkeep your exterior lighting. Some LED products have anticipated life of 50,000 hours and up. Even some fluorescent lamps advertise ‘extra-long life’ nearing 40,000 hours of burn time.
- As lamps get older, their light output decreases, but they still use the same amount of energy. When all your lamps are upgraded or retrofitted at the same time, it is a good idea to plan on a group relamp. This means instead of replacing lamps as they burn out (spot relamp); you choose to relamp the entire system at the 70-80% rated lamp life. By adopting this procedure you ensure regular intervals of maintenance are planned in your budget, and you give yourself the opportunity to make planned improvements or upgrades to your lighting system at the point of greatest return.
HOW TO SAVE ENERGY, GET THE LIGHT YOU NEED AND CONSERVE THE NIGHT SKY
Design your outdoor lighting for maximum efficiency and night sky conservation by choosing the right fixtures and the right system layout. Most lighting contractors will be able to provide you with solutions to meet these needs and a model that shows anticipated light levels. If a comparison between your existing and proposed new lighting systems is available, you will likely be surprised to find out how many inefficiencies and potentially light-polluting issues can be resolved with energy-saving fixtures that are built to reduce glare and light trespass. Consider these elements, plus improved safety and maintenance savings when you are ready to make changes to your exterior lighting system. The decision between upgrading and not upgrading gets easier the more you know!