LED Street Lights Making Streets Brighter
Street lights have a very obvious purpose that is lighting up the walkways, driveways, and other similar areas for ensuring a safe driving and walking experience for the passersby.
The main aim of street lights is to make all the objects under them clearly visible so that any potential obstructions or hazards can be easily identified and avoided. Several studies have shown street lights cause around a 40% reduction in car accidents.
Street lights must be installed to save passengers on any street safer against accidents and further damage. You may think that higher brightness is all that is important for street lights but that is not true entirely.
In fact, brighter lights increase the risk of shadow spots that become blinding for drivers. This is one of the many important factors that need to be considered while picking the perfect street lights. We are going to do a quick rundown on such factors below:
- The light output of the bulbs
- Reflection value of the particular target surface
- Ability to render colors
- S/P ratio of light and mesopic vision
- The ratio of maximum lumens, average lumens, and minimum lenses
- Uniformity of light distribution
- Fixture angle cut off
- Mounting pole height: The perfect lighting density can be achieved with optimum pole height. This is because light density starts decreasing with the increase in the height of the mounting pole.
The brightness of roadways or street lights denotes their total light output. You may have come across many streets and roadways lighted by the metal halide lamps.
These lights come with a lot of challenges that we will mention later but the most problematic one is the harsh glare they cause to the head-on onlookers. So, what can be done to avoid this? The answer is LED street lights.
Brightness of the Street Lights
The Angle Made By Light above the Nadir
The term Nadir is used in the lighting world and it denotes the angle that exists in the downward direction from the center of any light spot. This point lies perpendicular to the surface.
The IES or Illuminating Engineering Society is a non-profit organization responsible for curating lighting standards. It uses nadir for qualifying street lights as non cut off, semi cut off, or full cut off.
We have included a table below that shows the relation between light level percentages and luminaries classification.
% Total light output at 90° from Nadir
Percent of Total Candlepower at 80° from Nadir
The full cut off lights can be seen as being the downward-pointing light sources. This is crucial for Dark Sky regulations (mentioned later) as it causes the minimization of unnecessary light dispersion towards the sky. An added benefit is that they allow the usage of lower wattage lights because light wastage is a rare case here.
You can make the light sources more focused and directional by equipping them with a light shield simply. A light shield boosts their brightness even with lesser lumen capacity and decreases harsh light production. In place of all this, you can simply use LEDs that are built directional. They promote improved optic quality and lifted light angles for great outdoor lighting.
The IES or Illuminating Engineering Society has recently become more vocal about the importance of BUG ratings for street lights.
The BUG rating system is highly comprehensive at rating the lights on three unique standards- glare, up-light, and backlight. However, we will be discussing the previous classification only since it is still being used by the municipalities.
What Makes The Full Cut Off Lights So Crucial?
To help savings and minimizing light pollution in the environment is the main aim of full cut-off lights. This is closely related to Dark sky complimenting.
The concept involves the making of skies ‘night friendly’ to make heavenly bodies clearly observable to astronomers and minimization of anthropogenic lighting effect on the circadian rhythm of nocturnal earthly bodies and all this is achieved by freeing of skies from ambient light levels.
The basic idea is to reduce the contribution of light fixtures towards environmental light pollution. These regulations are strictest in coastal areas but must be practiced elsewhere too.
This is the picture of San Jose during the night and you can clearly see the light emanating from the city fixtures that are lighting up the sky. This is light pollution for the night sky that the astronomers and wildlife experts concern about.
You may think if wildlife is no concern for the cities facing light pollution but don’t ignore the trees that get affected too. All these issues can be avoided with the installation of full cut off lights.
The crucial and only reason why full cut-off lights must be used is that probably the only lights that are legal in the majority of areas around the world are these full cut off lights. Take the example of countries like Colorado and Douglas County that have lighting codes mentioning the sole use of full cut-off lights defined by IES for outdoor lighting.
Street lighting goes beyond ensuring safer driving and walking experience for nighttime passengers towards securing clearer and star-studded sky views for us Americans. You may find it surprising that mere tilting or shifting of full cut-off lights can be a violation of the country lighting code.
Various Luminaries and Their Light Footprint
The figure above describes the most popular luminaries’ varieties and their distinctive installation spots on the roads as per the IES standards. This depicts the distinctive working processes of luminaries in various situations.
Type 5 lights work better for installations to achieve a 360-degree brightness footprint in places like roundabouts or 4-way stops and type 1 light work better for achieving better light footprints on areas like road medians.
The Major Hurdle in Calculating The Light Output Of Fixtures In Lumens
The basic presumptions on which the calculation method of lumen output rests are equitable light quality and absence of light reflection. Theoretically speaking, the amount of light reflection varies according to the color of the particular surface and this also affects the brightness levels generated.
For instance, if yellow light is falling on an object of green color, the light will get absorbed and cause the object to appear black rather than its original color.
However, the reality is that greener objects, like leaves, are replete with multiple pigmented substances like xanthophylls, carotenoids, chlorophyll, and others that cause some reflection of the yellow light and appear grayish as a result. This makes higher luminosity output important from the roadways LPS fixtures.
LPS fixtures generate single colored light in the whole spectrum. At the same time, LEDs generate a more whole light spectrum. This causes higher contrasting and highlighting of the color differences in target objects even with lesser lumens and the onlookers’ experience improve optic power and securer feeling.
Another factor that makes the color perception of objects better is CRI or Color Rendering Index. Read here to know about CRI in greater detail but you must know that CRI is a measurement scale of light quality. CRI makes lights brighter with lesser lumens and this directly impacts the stimulation of rod cells in human eyes and this.
Here is a picture from Lincoln Ave you can see. The first three lights with left, right, and left signs are LEDs while the others being metal halides. This is because LEDs generate even distributed light that also is less glary. Their energy consumption is also lesser than metal halides. However, the metal halides that are used on the roads give a greater glare that impacts visibility. This is the reason why metal halides are not good for driveways.
To save such situations and make roads safer for people, numerous municipalities carried out major retrofitting drives. However, this is an old incident, and the fixtures installed back have come off their ages and utility as well. It is finally high time that the lights must be changed with the better-LED street lights.
It is equally important to consider the future developments in lighting that can take place while choosing LED lighting systems. Some such important developments include:
1. Intelligent lights
These are advanced LEDs fixed with motion sensors that render them the capability to generate various light outputs with no impact on brightness as per the ambient light levels.
Such technologies can be used further to equip the sensors for giving light outputs as per light levels and do all of this within minimized energy consumption according to the levels of natural light outside.
2. Multi-functional lights
These lights can be used for gathering information on different things like weather and traffic, etc.
3. Solar panels
Lights can be fixed with solar panels for reducing the risk of environmental light pollution.
The Right Light Dispersion for Street Lights
There are certain arrangements you would need to do while installing the street lights to make them anti-glare and generate evenly distributed light so that the street becomes safer for the passengers. We are talking about the light rays generated beyond 75 degrees from the Nadir that are harmful.
This light is glaring and harmful to drivers. This is why LEDs are a better choice for street lighting as they are anti-glare and produce balanced light. At the same time, HPS fixtures produce much higher glare due to their light rays being angled beyond 150 degrees.
This is the picture of a light setting that has the wide-angled HPS fixtures being used in it. You can notice the high amount of light wastage. The houses near the street have their curtains drawn mostly to save their windows from being unnecessary lit all the time due to the high light distribution. This further causes light pollution affecting nature experts and astronomers too.
This can be eliminated with the LED lights that give focused and directional lighting. The houses near the streets won’t need to hide their windows with curtains like in the case above anymore since the lights won’t be reaching anywhere but on the target space. This also causes lesser lumens requirement since the light is being used for the set purpose only.
Uniform Light Dispersion
It is only after the installation of the street light that you can assess the uniformity of light dispersion.
Uniformity comes with a balance between several factors like light optic properties, luminary reflector’s quality, crossing areas between the bulbs, and others. The following three ratios determine light dispersion uniformity:
- The ratio of average to minimum light intensity
- The ratio of maximum to minimum light intensity
- The ratio of maximum to average light intensity
The first two ratios can be determined easily which makes them more preferable.
Light dispersion uniformity plays a crucial role in glare reduction. Glare decreases the amount of light reaching the eyes by impacting the pupils into shrinking.
Some of the most popular methods of avoiding glare include blinking, squinting, wearing sunglasses for lowering the brightness in the whole vision spectrum, using various devices like peak caps for reducing the brightness part of the visibility spectrum. However, none of these methods come in handy to the night time street passengers.
Comparison of HPS and LED Street Lights
Municipalities are on their way to transform the streets with boosted safety measures and changing from HPS to LEDs is one of the major decisions they are taking. Even though the energy-efficiency quotient of LEDs is visibly higher, lot more things need to be considered.
The National Lighting Product Information Program or NLPIP discusses these issues out in their 2010 publication. Their study was based on eight street light samples belonging to top companies and the following were the observations:
- The output of LED street lights is lower. This can be a deterrent but not a surprise altogether because the labels on the LEDs displayed their lower lumens as compared to the target HPS fixtures.
- LED street lights promote savings. This is completely unsurprising. LEDs need to be installed at closer gaps despite them being highly bright than the HPS fixtures. This led the NLPIP to worry about the energy savings rising due to the extra lights that would need to be installed. However, the final result was that LEDs remained more energy-efficient even with the additional numbers.
- LED companies prefer fixture to have lower lumen levels. You need to still have LEDs with suitable lumens to match the HPS fixtures they are replacing even after being spaced similarly.
Overall, you will find out the initial cost to be much higher when carrying out the LED lights conversion. However, even the studies of NLPIP approved that the lifespan and efficiency of LEDs are much higher than the conventional HPS lights. Thus, LEDs are a better option for street lighting for long term benefits.
What Is The Cost For Street Light LED Conversion?
1. The initial cost of items like electrical wires, poles, and bulbs plus installation cost
On average, it takes around $4000 for the installation of a single light pole. This cost can vary depending upon the pole height, the foundation required, the distance of the pole from the electricity source, light efficiency, and light power ratings.
Usually, in rural areas, electricity sources placed farther which requires longer wire stretching to give power to the lights. To avoid such a situation, solar-powered lights can be used in such areas but the higher cost is their downside.
2. Cost of energy consumption by the lights
Consider replacing a metal halide bulb without changing the fixture at all with a 100 watt LED Street Light, this means that the bulb will produce around 15550 lumens of higher quality light by consuming 100-watt power.
Calculating this way, around 197000000 kWh of power is used by the 209000 street lights installed in Los Angeles at the rate of 250 watts per hour. To save on this enormous energy consumption is the prime motive behind Los Angeles and another shifting to LED lighting systems.
|LED Street Light||High Pressure Sodium||Mercury Vapor||Incandescent|
|Actual light availability (Lumens)||15,500||14000||14000||2800|
|Hours of operation per night||10||10||10||10|
|Cost of electricity ($/kWh)||0.10||0.10||0.10||0.10|
|Annual Consumption (kWh)||383||913||1460||1460|
|Annual electricity charges ($)||38.3||91||146||146|
|Cost per 100 Lumens||0.24||0.65||1.04||5.21|
|Average Life Span (years)||20+ *||5||4||3|
*rated L70 of 100,000 hrs, 3650 hours per year average use
3. Cost of bulb disposal and changing fused bulbs
You may have not thought about it earlier but even disposing and replacing the street lights incurs a charge that is higher too. The average money spent by Los Angeles in controlling and maintaining around 209000 street lights is 42 million dollars. This equates to $200 spent per light every year.
The primary reason behind this high cost is pole height because to deal with the lights at such a height requires machines like cherry pickers and trucks to carry the workforce or lift there.
A comparative study was done by U.S. Naval Observatory Flagstaff Station personnel Christian B. Luginbuhl of the various outdoor lighting systems led to him concluding that LPS fixtures have a lower lifespan than the HPS fixtures by nearly 6000 hours and they also need higher maintenance.
This is one crucial reason other than no color rendering capacity that makes Low-Pressure Sodium lights lesser preferable. At the same time, Metal Halides and HPS have an average lifespan of nearly 12000 to 15000 hours. Even worse is their lumen depreciation that is L50.
Calculating replacement cost of one bulb:
Cost of the new bulb + Payment of two mechanics + Rent of man lift + Cost of renting a truck = +/-$800 (We have assumed the cost of a single bulb and ballast to be around $150).
The unfortunate case in many cities is that the municipalities have to meet the demands of higher or at least average quality services in the limited funds that are available. Such situations can be made better with the newer lighting technologies.
There are remote control systems that can reduce the physical maintenance cost of street lights. A good example is an LED lighting system that has a higher average lifespan with about ten extra years. The light systems of certain cities like Ann Arbor require higher maintenance which can be dealt with modern lighting technologies.
Maintenance Of Street Lights
Keeping the street lights well maintained plays a crucial role in making the streets safer for the passengers and the operation of the light for the longer term.
In the case of LEDs, the maintenance needs are low and they keep giving brighter light for a long time too but there are still many things to take care of. You can boost the life of bulbs along with reducing the damage risk by regularly maintaining them. The table below can be your checklist to follow.