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| Fig. 1:US Market share of different lighting technologies from 2010, 2015, and 2020. [6] (Courtesy of the DOE) - This figure requires attribution. - RBL |
General illumination is so ingrained into our everyday lives that it is easy to miss the underlying physics and technology utilized to make such illumination possible. Light Bulbs are the most common appliance for lighting. The technology encompasses several sub-categories that each have their benefits and drawbacks with the general trend being increased energy efficiency and lifespan as the technology evolves.
There are many potential characteristics light bulbs have that make them relevant to different applications like shape or color but the two most relevant to performance are the LPW (Lumens per Watt) and lifespan. Lumens are a measurement of how bright the bulb is so measurement for efficiency is how many Lumens are generated per Watt of energy. A light bulbs lifespan is how long it can be turned on, typically measured in hours. This determines how often a consumer needs to purchase a replacement bulb.
The first light bulbs were incandescent bulbs. These bulbs rely on electric resistive heating on the bulbs filament which creates an excited state within the atoms of the material which are partially relieved as photon emissions, producing light. [1] Tungsten wire is typically used as a filament for its high melting point and the lowest rate of evaporation. [1] A major drawback of this technology is that the vast majority of the energy is spent on heating the filament. Only 10% of the energy used creates visible light. [2] The intense heat on the thin filament also leads to a poor lifespan of typically under 2,000 hours. [3] Their LPW, according to a 2017 report, is about 10. [4] Incandescent light bulbs are largely considered dated because of their short lifespan and low LPW. Halogen filled incandescent bulbs are an improved version of the traditional incandescent bulb that use 30% less energy but still underperform when compared to other alternatives. [5] Both incandescent and halogen bulbs have fallen out of favor with them comprising 12.6% and 6.6% of installed units respectively in the residential market and neither breaking 1% market share in the commercial market because of their high energy consumption. [6]
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| Fig. 2:The amount of energy consumed by different lighting technologies in the US from 2010, 2015, and 2020. [6] (Courtesy of the DOE) - This figure requires aattribution. - RBL |
Fluorescent bulbs are filled with a mixture of gases that when passed through an electric current emit ultraviolet light. This light is then filtered by the coating of the bulb to produce visible light. Fluorescent lighting is popular in the commercial market making up over 50% of installed units in 2020. The majority of those installed units were T4 bulbs which are the long cylindrical bulbs common in office spaces. [6] However, the colder lighting produced by fluorescent bulbs makes them less popular for the home. These bulbs convert 85% of the electricity consumed into light which makes them far more efficient than incandescent bulbs. [7] The common household variant of these bulbs is, referred to as a compact fluorescent light (CFL), has a LPW of 59.8. [5] CFLs have a lifespan of 8,000 to 10,000 hours. [3]
Light emitting diodes (LEDs) are a form of solid-state lighting and are in most use cases the most efficient and longest-lasting lighting technology. LEDs are a type of semiconductor diode that like all diodes only permit current to flow in one direction. The diode contains a PN junction that facilitates the injection of charge carriers (electrons and holes) into the active region of the diode from the surrounding layers. In this active region, the recombination of these carriers generates light through electroluminescence. [8] This process is efficient and creates little energy loss to heat. The LPW of LEDs ranges but a 2017 DOE report gave an average of 77.6 LPW. [4] Most white LEDs have an estimated useful lifespan between 35,000-50,000 hours but certain models have lifespans of over 100,000 hours. [3] However, these numbers are likely to be larger by now and increase in the future as unlike incandescent or fluorescent bulbs, LEDs are not a fully mature technology. LEDs are equally popular in both residential and commercial applications. They comprised about 47.3% of installed units in residential spaces and 47.6% in commercial spaces with the main difference being that commercial spaces use mostly linear LED lighting as opposed to traditional bulbs. [6]
Fig. 1 shows the market share trends between different lighting technologies in residential and commercial markets between 2010, 2015, and 2020. [6] In residential spaces LEDs are becoming more common while CFLs and incandescent bulbs are falling out of favor. In commercial markets LED market share is increasing, linear fluorescent lighting is holding its share, and incandescent lighting is nearly eliminated.
Fig. 2 shows the annual energy consumption between different light sources in these markets. [6] Although total lighting units have increased, total energy consumption has fallen. This is largely due to the high prevalence of more efficient technologies like LEDs and fluorescent lighting. In the commercial space higher-cost forms of lighting are nearly eliminated. This diagram also highlights how inefficient incandescent lighting is. Even though incandescent sources only make up a fraction of the total residential market share they consume a greater share of electricity than any other lighting technology.
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| Fig. 3:General purpose lightbulb sales by lightbulb type in the pacific northwest residential market from 2011 to 2015. [11] (Courtesy of the DOE) |
Regulation at the state and federal level has also played a role in the phasing out of incandescent lightbulbs. The Energy Independence and Security Act of 2007 (EISA) begun forbidding the sale of many inefficient incandescent bulbs in the early 2010s. [9] Some individual states have their own laws for removing inefficient bulbs from market. California's recent Assembly Bill 2208 begun phasing out the sale of certain CFL bulbs at the state level. [10] Lighting sales data demonstrates the impact of EISA and state level regulation on incandescent bulbs. The Bonneville Power Administration (BPA), a federal agency that generates and delivers electricity to the Pacific Northwest, used retail sales data compiled by the Northwest Energy Efficiency Alliance, market actor interviews, and a literature review to garner insights into the lighting market in the pacific northwest. Their residential sales trends indicated that general purpose incandescent lightbulbs dropped from 68% market share in 2011 to 12% in 2015. [11] Fig 3. displays the market's movement away from incandescent bulbs into halogen, CFL, and LED bulbs for residential lighting. [11] These regional market trends clearly illustrate the decline of incandescent bulbs. It will be interesting to see if similar patterns emerge for other lighting technologies that are starting to see phasing out polices. There is likely an untracked market of incandescent bulbs that lives outside the purview of organizations like the BPA and DOE but nonetheless these broader market trends created by regulation and new technologies persist.
The drop in energy consumption from commercial and residential lighting is about 280 TWh as seen in Fig 2. [6] This is about 6% of the 4,284 Terawatt hours of energy consumed by the US in 2020. [12] While this is a significant energy savings, development and emergence of power hungry technologies like AI and cryptocurrency are likely to increase energy consumption more than any savings squeaked out by more efficient lightbulbs. This does not discredit how much more efficient lighting technology has become but there is more sectors to examine for energy consumption other than lighting.
There is often little emphasis on how one's immediate surroundings are being illuminated but lighting technology has been evolving in plain sight. By exploring the various technologies that humanity has used for lighting it is clear that there has been a great deal of engineering and physics ingenuity into making more efficient and longer lasting sources of light. Incandescent bulbs and LEDs are two vastly different solutions to the same problem and it is interesting to look into all these technologies, pick them apart, and draw conclusions as to why our modern lights compare.
© Cristobal Garcia. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. MacIsaac, G. Kanner, and G. Anderson, "Basic Physics of the Incandescent Lamp (Lightbulb)," Physic Teach. 37, 520 (1999).
[2] "Lighting Efficiency," Pew Center on Global Climate Change, April 2011.
[3] "Lifetime of White LEDs," U.S. Office of Energy Efficiency and Renewable Enegy, September 2009.
[4] N. Buccitelli et al., "2015 U.S. Lighting Market Characterization," U.S. Office of Energy Efficiency and Renewable Energy, November 2017.
[5] N. Popovich, "America's Light Bulb Revolution," New York Times, 8 Mar 19.
[6] "2020 U.S. Lighting Market Characterization," U.S. Office of Energy Efficiency and Renewable Energy, April 2024.
[7] L. Dikeou, "Efficiency of Incandescent Light Bulbs Vs. Fluorescent Light Bulbs," Physics 240, Stanford University, Fall 2014.
[8] B. Bonanni, "LED Light 'bulbs," Physics 240, Stanford University, Fall 2016.
[9] "Energy Independence and Security Act of 2007," Pub. L. 110-140, 121 Stat. 1492, 19 Dec 07.
[10] "AB-2208 Fluorescent Lamps: Sale and Distribution: Prohibition," Chapter 409 (Cal. Stat. 2022), September 2022.
[11] "Residential Lighting Market Characterization Study," Bonneville Power Authority, DOE/BP-4795, April 2017. p. 2.
[12] "BP Statistical Review of World Energy," British Petroleum, June 2022.