LED Lighting *Efficiency - Performance - Longevity*
LEDs are making major inroads to general street, sidewalk, and parking lot illumination as their brightness is getting close to HPS, MH, or CFL lighting. LED will very rapidly replace most other forms of street lighting due to improved color rendering characteristics, and more importantly, a very large improvement in overall efficiency.
- LEDs provide a longevity that is up to 20 times that of standard incandescent lamps, translating to low maintenance.
- LEDs are solid-state devices, meaning no moving parts, glass or filaments to break.
- LEDs don't waste energy in the form on non-lighting producing heat. Therefore they are cool to touch and as a result, lighting fixtures and lenses are cool.
- LEDs are small in size and resistant to vibration or shock.
- LEDs contain no mercury or lead and are environmentally friendly.
- LEDs are more efficient, using up to 09% less energy than other light sources based on watts.
- Superior ROI (return on investment), inclusive of initial capital, energy, maintenance and replacement cost.
- Functional and attractive light using existing fixtures and spacing
- Adequate light output, distribution pattern,and uniformity
- Long Life - minimum 80,000 hours between relamping
- Energy Efficiency - more efficient than existing solutions
- Controllable light pattern - dark-sky friendly, with minimal light trespass
- High CRI (color rendering index) - beautiful, comfortable, clean, clear white light
Metal Halide Lighting
History of Metal Halide: About 40 years ago General Electric began to experiment with more complicated mixtures inside of mercury arc lamps, in order to get better efficiency and a more pleasing, white color. Starting with mercury metal vapor, they added iodine salts of other metals (indium, scandium, sodium, and thallium). Iodine is one of the halogen elements, and thus a compound of a metal and iodine is called a "metal halide" salt. By 1962 they had applied for patents on this varient arc lamp, which they called a "Multi Vapor Metal Halide" lamp. Metal Halide lamps are more efficient than their parent, the mercury vapor arc lamp. They can be as much as 50% efficient in turning electricity into light. They tend to not be quite as efficient as the high pressure sodium vapor lamp, but they put out a much more white light. This white light does tend to be somewhat biased toward appearing a bit bluish. These lamps have in places replaced sodium lamps for use in street lights.
Metal halide lamp (MH) 
streetlights have illuminated the roadways and parking lots in recent years. Metal halide has long been popular in business installations and can be found in warehouses, schools, hospitals and office buildings. Unlike the old mercury lights, metal halide casts a true white light. It is not nearly as popular as its sodium or mercury counterparts, as it is newer and less efficient than sodium.
Metal halide lights have also been used for retrofitting. Virtually all fixtures that are converted to metal halide have previously been lit with high-pressure sodium (HPS). MH lamps suffer color shift as they age though this has been improving. Actual life expectancy is about 10,000 to 12,000 hours on average. High cost and low life hours has kept them from becoming popular municipal lighting sources even though they have a much improved CRI around 85. Therefore, the use of metal halide is limited mainly to city and high end street lighting.
Features and Benefits:
- Produces a pure white light
- Enormous amount of light with excellent color rendering
- Bulbs last 6 times longer than incandescent bulbs
History of the High Pressure Sodium: Further experimentation with metal vapor arc lamps resulted in the high pressure sodium lamp. This produced a distinctive yellow color of light. High pressure sodium metal arc lamps have been designed to be very efficient. Some can turn over 50% of the electrical power put into them into visible light. Their yellowish light is much more psychologically warm and pleasant. They replaced mercury vapor in streetlight applications. Around 1970, a new streetlight was put into service: The high pressure sodium (HPS) light. It was initially disliked by most residents because of its orange glow, but the sodium vapor streetlight has since become the dominant type on American roadways and most people have become accustomed to the orange/yellow glow. It is by far the most efficient light source when compared to Mercury Vapor (MV) and Metal Halide (MH). Color Corrected Sodium Vapor Lights exist but are expensive. These "color corrected" HPS lamps have lower life and are less efficient.
There are two types of sodium vapor streetlights: high-pressure (HPS) and low-pressure (LPS). Of the two, HPS is the more-commonly used type, and it is found in many new streetlight fixtures. Sometimes, older (pre-1970) fixtures may be retrofitted to use HPS lights as well. Virtually all fixtures that are converted to HPS have previously been lit with mercury vapor. HPS lamps have slightly different electrical requirements than do the older MV lamps. Both HPS and MV lamps require a transformer or ballast to change the voltage and regulate the current, however, HPS lamps also require an electrical "starter" circuit -- much like older fluorescent lamps in residential use. MV lamps do not require a separate "starter" circuit because they have a special starter element within the bulb used for striking the arc. MV lamps slowly dim over time, and a twenty-year-old lamp may emit a very pleasing, but useless, soft glow, rather than the powerful blue-white light of a new MV lamp. The yellow-spectrum HPS lamps also slowly dim over time but are known for "cycling," where the lamp cycles on and off when it has reached the end of its life cycle. When cycling, the arc within the lamp extinguishes and the lamp must cool down before the starter circuit initializes a new arc.
HPS lamps by and large have a longer lifespan as do MV lamps, and they do give increased light and efficiency. At end of life MV lamps just become dimmer and sometimes color shifting towards the green end of the spectrum and continue to consume the same amount of electricity. HPS lamps begin to suffer end-of-life cycling before the amount of useful light becomes visibly diminished.
Color Rendering-High pressure sodium lamps produce a color of light that is considered less pleasing than whiter lights. The CRI for high pressure sodium lamps is generally lower than metal halide, however the HPS lamps are more energy efficient than metal halide.
Features and Benefits:
- Produces a golden-pink cast
- Least expensive of any HID lighting
- Bulbs rated at 24,000 hours
Compact Fluorescent Lamps
History of the Compact Fluorescent Lamp: The low pressure mercury arc lamp is the direct parent of today's modern fluorescent lights. It was discovered that low pressure arc lamps would put out large amounts of ultra-violet light. By coating the inside of the light bulb with a fluorescent chemical (one that absorbed UV light and re-radiated that energy as visible light) it made an efficient light source. Early fluorescent lamps used beryllium in their fluorescent material, but later this was replaced with fluorescent chemicals. Combined with modern electronic technology, the latest fluorescent lamps are as much as 40% efficient in turning electrical energy into light. However, they can't be made to produce a bright point source of light that can be focused into a beam.
Compact fluorescent lamp/lighting (CFL) 
is being used more frequently as time has improved the quality of these lamps. These lamps are used on municipal walkways and street lighting though they are still rare at this time. Improvements in reliability have been made in the last few years. Some issues with them are high heat build up in the self contained ballast, low life/burnout due to frequent cycling (on/off) of the lamp, and the problem where most fluorescent sources become dimmer in cold weather (or fail to start at all). CFL efficiency is high and CRI is excellent around 85. CFL produces a color temperature around 3000 K with its light being "soft white" around that color temperature. Higher color temperatures are available.
