Energy Efficiency
To make a claim of energy efficiency, the two products being compared must produce equal quality light. A High Pressure Sodium street light produces uniform illumination, amber color, sine wave flicker, and a gentle light. A typical LED street light produces non-uniform illumination, white light with high levels of hazardous blue wavelength, digital flicker, an intense light, often associated with pain, and for some individuals, seizures or migraines. Thus, the claim that LED street lights are energy efficient is false.
An example of actual energy efficiency would be to take a 100 watt street light that is emitting 5,000 lumens, and then clean out the bugs and dirt and wash the lens so that the same 100 watt street light is now emitting 7,500 lumens. The quality of the light is the same or better, but more light is output for the same amount of energy input. Another example would be to replace the 100 watt street light with a 50 watt street light if the 100 watt street light is producing more light than is necessary and the 50 watt street light still provides the same quality of service.
Energy Conservation
An example of energy conservation is turning off the street lights because they are little used. Society generally turns off the water hose when it is not in use to conserve the water. Curiously, the same action is often not the case for street lights. Conserving energy by turning off street lights after 10pm would save significant amounts of energy, greatly reduce the carbon footprint, would benefit public health, and protect the night time habitat.
Luminous Efficacy
Luminous efficacy is the number of lumens emitted per watt of energy used. Luminous efficacy is not equivalent to energy efficiency because luminous efficacy only measures the energy used, and not the quality of the light. Here is a table of luminous efficacy values for street lights. The efficacy of these street lights depends on many factors, so general ranges are listed.
Low Pressure Sodium: 180 lumens per watt
High Pressure Sodium: 80 to 120 lumens per watt
Blue/White LED: 80 to 120 lumens per watt
Amber LED: 60 to 110 lumens per watt
Refractive Lenses
The image below shows the refractive lenses used in a typical HPS streetlight. These refractive lenses distribute the light evenly across the surface to be illuminated.
The photo below shows a comparison of the individual LED diodes for an LED street light and none of the refractive lenses that are used with a typical HPS street light. The result is that that each individual LED diode produces a hot spot beam, with little mixing. The high luminance, tiny diode, and discrete emitters creates a light that the street lighting company Cree Lighting calls “dangerous”.
Zebra Pattern
The Before photo below shows an unshielded High Pressure Sodium street light with a Correlated Color Temperature of approximately 2200K which provides uniform illumination containing little hazardous blue wavelength light, but creating unwanted glare and light pollution. The After photo shows an unshielded LED with a CCT of approximately 3000K providing non-uniform illumination which creates an unsafe zebra pattern. The use of blue wavelength light is hazardous to human and ecosystem health and increases light pollution due to the use of high energy of blue light.
Blue Wavelength Light
At least 2,697 peer-reviewed research studies have shown that blue wavelength light is hazardous to our health. Blue light can cause cellular death in the eye and blue light at night interferes with cellular processes, leading to significant increases in mood disorders, cancer, diabetes, heart disease, premature birth, and early mortality. While all artificial light at night can be hazardous to human and ecosystem health, any street light with a color temperature exceeding 2200 Kelvin must be considered to be a unacceptably hazardous to human and ecosystem health.
Rod Cell Bleaching
Rod cells in the eye will bleach almost instantly when exposed to bright light, rendering these cells non-functional. The recovery process takes about 45 minutes. Thus, any claim that LED street lights are better for night time vision due to our use of rod cells at night becomes negated when the LED street light bleaches the rod cells with high luminance, blue/white light.
Resources
February 2, 2024 – The Streetlight Effect – Modern Considerations of Early Observations – Discussion of gaze behavior and uniform illumination.
October 9, 2023 – Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 people – Increased exposure to light at night increases a person’s risk for psychiatric disorders such as anxiety, bipolar and PTSD severity as well as self-harm.
October 4, 2023 – Lights should support circadian rhythms: evidence-based scientific consensus – 2,697 peer-reviewed publications show that blue light is harmful.
July, 2023 – How a Simple Concept Enabled a $50 Billion LED Streetlight Scam that Changed our World – This 19 minute video describes some of the false claims of LED street lighting.
May, 2023 – The LED’s Challenge to High Pressure Sodium (Response / Debunking / Topic Expansion) – This hour-long video debunks many myths about blue rich LED streetlighting.
March, 2023 – A Multi-Field Analysis of Street Lighting in Grand Rapids, Michigan – A detailed analsysis showing why LED streetlights with blue wavelength light are unsafe and why Low Pressure Sodium is most energy efficient and safest type of street lighting.
December, 2021 – Is Street Lighting Damaging Our Health? The first documented admission by an LED lighting company, Cree Lighting, that the industry has been using the wrong metrics to measure LEDs.
2020 – Iowa State Institute for Transportation Street Lighting Design Manual – Contains luminous efficacy values for different types of street lights.
January 9, 2018 – Road Lighting Research for Drivers and Pedestrians – Admitting that the standards do not match the empirical realities.
Flagstaff Dark Skies Low Pressure Sodium Lighting – Provides details about why LPS is the best choice for street lighting.
The Low Pressure Sodium Lamp – Describes the “remarkable efficacy” of LPS.