LED street light
An LED street light or road light is an integrated light-emitting diode (LED) light fixture that is used for street lighting.
Type
Low energy consumption: Many LED lighting retrofits have been claimed to dramatically reduce energy use.
[6]
Long and predictable lifetime: The projected lifetime of LED street lights is usually 10 to 15 years, two to four times the life of currently prevalent HPS. (LEDs themselves do not generally fail or “burn out” in a way comparable to other technologies, and barring catastrophic failure of other mechanical or electronic components of the LED fixture, lifetimes are typically set by a decrease in luminous output of 30%. But the functional lifetime of an LED fixture is limited by the weakest link; associated drive electronics are typically projected to last about 50,000 hrs. It is important to understand that no LED streetlighting products have been in service long enough to confirm the projections). If realized in practice, the less frequent need to service or replace LEDs will mean lower maintenance cost.
More accurate color rendering: The is the ability of a light source to correctly reproduce the colors of the objects in comparison to an ideal light source. Improved color rendering makes it easier for drivers to recognize objects.
color rendering index
Quick turn on and off: Unlike fluorescent and high-intensity discharge (HID) lamps, such as mercury vapor, metal halide, and sodium vapor lamps, which take time to heat up once switched on, LEDs come on with full brightness instantly.
compliance: LEDs don't contain mercury or lead, and don't release poisonous gases if damaged.
RoHS
Optically efficient lighting equipment: Other types of street lights use a reflector to capture the light emitted upwards from the lamp. Even under the best of conditions, the reflector absorbs some of the light. Also for fluorescent lamps and other lamps with phosphor coated bulbs, the bulb itself absorbs some of the light directed back down by the reflector. The glass cover, called a refractor, helps project the light down on the street in a desired pattern but some light is wasted by being directed up to the sky (light pollution). LED lamp assemblies (panels) can send light in the desired directions without a reflector.
Higher light output even at low temperatures: While fluorescent lights are comparably energy efficient, on average they tend to have lesser light output at winter temperatures.
Many people dislike the ambiance produced by LEDs with color temperatures of 4000K or higher. 2700K and 3000K LEDs are mostly used for indoor lighting.[8]
[7]
The initial cost of LED street lighting is high and as a consequence it takes several years for the savings on energy to pay for that. The high cost derives in part from the material used since LEDs are often made on or other expensive substrates.[9]
sapphire
As a result of the , the dark-adapted human eye is very sensitive to blue and green light that LED street lights emit in large amounts, as compared to the yellow and orange high-pressure sodium lights that are typically being replaced.[10][11][12] This magnifies the effect of light pollution - particularly sky glow.
Purkinje effect
The major increase in the blue and green content of artificial sky glow arising from widespread LED lighting is likely to increase impacts on bird migration and other nocturnal animal behaviours.
[13]
Blue-rich light pollution from LED streetlights can disrupt circannual rhythms and cause the complete loss of an organism's seasonal clock. This impacts important behaviors such as feeding, reproduction, thermoregulation and hibernation. In some cases the failure to hibernate or properly thermoregulate due to this loss of seasonal timing can kill the organism.[15][16]
[14]
There is progressive wear of layers of in white LEDs. The change in color slowly moves devices from one photobiological risk group to a higher one.[17] Manufacturing problems can lead to defects of LED street lights resulting in delamination of the phosphor coating layer much sooner than the design life of the lights. This causes the white LED lights to turn blue or purple.[18] The issues of large scale defective lights happened in many cities in United States and Canada.[19][20]
phosphor
The blue-rich spectrum of LED streetlights is less effective than the yellow-dominant spectrum of Sodium lighting in producing a targeted luminance level on roadways, as the spectral reflectance of roadway pavement is higher for longer wavelengths of light. Due to this difference in spectral reflectance, much of the light produced by an LED streetlight is absorbed by the pavement rather than reflected.
[24]
LED streetlights produce greater levels of glare than previous sodium light sources. This is largely due to fixtures with smaller source areas resulting in increased luminance levels, a metric of light intensity. The blue-rich spectrum of LED streetlights also leads to increased levels of glare, especially discomfort glare.[26]
[25]
The blue-rich spectrum of LED streetlights leads to greater impacts of Rayleigh Scattering, where short wavelengths of light scatter within small particles more than long wavelengths of light do. This increased light scattering within the atmosphere leads to increased skyglow. During bad weather such as heavy rain, snow or fog, this scattering can create physical walls of light that obstruct vision.
[27]
As the human eye ages the lens of the eye yellows. This changes the spectral transparency of the lens to favor longer wavelengths of light, with significant losses in transparency for shorter wavelengths of light. Due to this spectrum-based loss in transparency the blue-rich spectrum of LED streetlights becomes less visible as an individual ages. For example in the eye of someone aged 50, the light transmission of a 4000K LED is 11% lower than that of a 2700K LED, relative to someone aged 25.[24]
[28]
U.S. Department of Energy reports on municipal LED lighting pilot projects: