- Welcome to Wednesday Nite at the Lab.  I'm Liz Jesse, the media specialist for UW Science Outreach.  On behalf of Wisconsin Alumni Association, Wisconsin Public Television, UW Madison Science Alliance, UW Madison Biotech Center, and UW Extension and Cooperative Extension, thanks for coming out to Wednesday Nite at the Lab.  We do this every Wednesday, 50 times a year.  Tonight, it is my pleasure to introduce Andrea Hicks.  Andrea grew up in Dearborn, Michigan, which I just found out tonight is right outside of Detroit.  I don't know Michigan very well, apparently.  She completed her PhD in civil engineering at the University of Illinois at Chicago and then completed a postdoc at the Institute of Environmental Science and Policy.  Her research at the UW, and maybe beyond, focuses on the environmental, economic, and social impacts of new technologies compared to conventional counterparts.  So I kind of thought of this like, we don't use Keurig at home because I know that conventional brewing is better. 

 So maybe that's kind of what she talks about.  Tonight, she's going to be focusing, and we're going to be talking a little bit about the history of artificial light and how it relates to sustainability of today's emerging lighting technologies.  So, here we go with the LED paradox.  Please join me in welcoming Andrea Hicks.  [audience applauding]  - Thank you for that warm welcome.  Can everyone hear me? Nods? Okay.  So, first, I'd like to thank the organizers of Wednesday Night at the Lab for allowing me this platform to present some work, and to thank all of you for being here to learn about the LED paradox.  So, a little bit about what we'll go over tonight.  We'll look at what is artificial light? What's the history of lighting in Chicago? It's a major city not so far from here.  It's a nice place to start. 

 Our consumption of light, what technologies changes mean, Jevons paradox, and novel consumption.   So, what is artificial light? This is the point where everyone's like, artificial light, it's in this room.  We have it.  I'll point to it.  So, to take it a more philosophical way, it renders the invisible visible.   It's safety.  It's traffic control signals.  I'm from civil engineering, so I have to throw in some examples like that.  It's street lights at night that encourage people to walk.  It's productivity. 

 Without artificial light, there would be no night shift at hospitals.  There would be no third shift at plants.  And it decouples us from the patterns of the sun.  We're no longer dependent on the sun as our sole source of light.  And here's a quote from Harold Platt, who wrote The Electric City in 1991, and that centers on Chicago and it's history of light.  We'll talk a little bit about his book to give some background context.  "But the bright lights of the city quickly became both a status symbol and a physical manifestation of progress, wealth, and amenities." So, light isn't just light.  It's a symbol of progress.  If you think about a cartoon, what happens when someone has an idea? They get the light bulb.  So it's more than just illumination. 

  So, this is a timeline of lighting in Chicago.  In 1878, Barrett demonstrated Brush's arc lamp.   And within a decade, there are almost 7,000 arc lamps built and operated in the city of Chicago at an annual cost of a million dollars, which is a lot.   "And so the electric suppliers..." This is also from Platt's book.  "...faced a consumer market with no bounds." And this is a question that will permeate our talk tonight.  What is saturation of light? When do we have enough light? How much light is too much light? But there were some problems with this arc lamp.  It was a fire hazard.  It was big.  You couldn't use it in a residential setting.  So, in 1880,  or 1879 depending,  Thomas Edison invented the first marketable incandescent bulb. 

  And Chicagoans suddenly had this choice, what kind of light do I want? Do I want electric light? Do I want a kerosene lamp? Do I want to go by the old gas lighting standby? And so these incandescent bulbs were much safer than arc lamps, and could be easily scaled to residential use.  But really, electric lighting was only for the wealthy at first.  It wasn't for the everyday person.   But, at the same point, there was this radical shift in psychological perception of interior lighting levels.  And this goes back to our question of how much light is enough light? How much light is too much light? So what had seemed all right before was dark, gloomy, and depressing.  So already we're craving more light, because we have more light.  Now, in 1893, Chicago's World Fair, Chicago was dubbed the city of light.  And, by 1912, about half of Chicago's middle class families had electricity in their homes and electric light.   So, look at that quote again.  It's a status symbol. 

 It's progress, it's wealth, it's amenities.  Light is more than just illumination.  It means we're moving forward.  And some photos from the World's Fair.  They're not great, but, you know, early 1900s.   And it was amazing.  We had all of this light.   So, before we start to talk about the actual consumption of light, some little background.  One unit I'll talk a lot about today is a lumen, and a lumen is an international standards unit for the measurement of brightness.  And another way to think about it, it's the light of one candle one foot away. 

  Although, I suspect most people don't compare their light bulbs to candles at feet.  Maybe people do, and that's okay.  And so it's a measure of light output, and it's a nice way when we talk about different efficiencies of lighting to compare them.  About 800 lumens is about a 60-watt incandescent, which translates into CFLs and LEDs.   So, this we're already using our lumen.   This is teralumen hours per year of light consumed in the United Kingdom.  It's a study by Tsao et al in 2010 that looks at the consumption of light over time and changes in technology.  So here we are transitioning from candles to gas, to kerosene, and eventually to electricity.   And the whole time we're consuming more light.   Yes, the lines go up, consuming more light. 

  And it's largely, this work by Tsao et al, was largely based on some earlier work by Fouquet and Pearson, that looked at the price of lighting.  So, how much per million lumen hours? We're using those lumens again.  So what's the cost of light, as we transition over time from gas light to kerosene light to electric light? And the point is, it's been going down, over time in the UK during this study, which ends at about 2000.   I see people talking, this is a good sign.   So okay, so we've been using more light and the cost of light has been going down, at least in the UK.  So, the Energy Information Administration very recently put together a chart of energy consumption in the United States starting from 1776,  which is nice.  Usually you can't find data, at least in engineering when I'm looking for something from the 1700s.  And, okay, so we consume more energy.  This is in quadrillion British thermal units.  And our energy consumption broken down by what we're consuming. 

 And over time, we've transitioned from coal to more toward natural gas and petroleum products.  So, okay, the question is, how much energy do we use for artificial light?  Is it a lot? Is it a little? Would we even see it on this graph? So, when I started studying this,  and the first data is from maybe around 2001, we were using 8.2 quadrillion British thermal units of electricity for lighting in the United States.  So, if you take a look, that is a little bit higher than nuclear energy consumption in 2015.   So, based on the premise of this talk, do you think it's gone up or down?  Some up? Shall we raise hands? Who thinks it's gone up? Okay.  Who thinks it's gone down? - [Audience Member] Are you asking input or output? - Total energy consumption.   - [Audience Member] So the energy input into it.  - Right.  And who doesn't know? [audience chuckling] That's okay.   So it's actually gone down, which seems a little counterintuitive with a talk called, The LED Paradox and the Rebound Effect.  But, in 2010,  about 7.5 quadrillion British thermal units were devoted to electricity for lighting, and in 2013, 6.9 quads,  which comprised about 18% of total US electricity usage. 

  So it's gone down.  Why are we talking about energy rebound and the paradox? We'll get there.   So, let's think a little bit about efficiency.  And, here, we've got a compact fluorescent lamp,  which was invented or inspired in 1973  during the oil crisis, and in 1974, made by an engineer at General Electric.   And in the 1980s, CFLs were introduced to the public.  So, who remembers that?  Okay.  Maybe half a dozen people, that's a good start.  And, but there were some problems.  They were expensive.  They were about $25-$35 per light bulb, and that number is a little fuzzy, because they were often subsidized by the electrical utilities. 

 They're blue.  They failed early, and they had inconsistent light input, output.  Not well received.   So, as we talk about lighting technologies,  let's talk a little bit about how they work.  So in an incandescent, which is sort of what we think of as the conventional technology, an electric current runs through the filament, heating it, and then it starts to glow and light is produced.  But what about a CFL?  So, in a CFL, it has this curlicue shape, right?  And an electric current goes through the argon and a small amount of mercury vapor, which is stored in the curlicue.  That generates invisible ultraviolet light that excites a fluorescent coating, which is on the outside, and produces light.   This is from the friendly folks at Energy Star.  So, what about LEDs?  So, LEDs, or light emitting diodes, and we'll talk about how they work in a second, are considered an enabling technology, because they enable other products and other technologies that would not be possible without them.  And this is a graph  from data mined from the US patent database on the percentage of light emitting diode patents per year, applications per year, broken down by the application's application. 

  So, what is the goal of this?  And you can see LEDs for illumination are near the top.  And illumination is what we primarily thought of for what we do with light.  You light a candle to have light.  You turn on an incandescent light bulb to have light.  But with LEDs, we start to have other options.  We have liquid crystal displays.  We have manufacturing, communication, military, medicine.  There's all, and novelties, which we'll talk about later.  There's some exciting novelties.   And so they have all of these properties. 

 They don't get really hot, they're small.  You can enclose them, and they can get wet.  And the first red LED came about in 1961.  So they've been around, but we're now just starting to use them for residential lighting applications.   So, how do LEDs work?  And I enjoyed this.  This is from howstuffworks.com.   And forgive me if you've spent time studying quantum mechanics.  This is just a very brief overview.  So, LEDs are semiconductors, and current flows through the diode, and the electrons move.   There's holes that exist at a lower energy and there's free electrons, and when the electron moves to a lower energy level, it emits a photon, which is light. 

  Very brief overview.   And that is, this a red LED,  but it doesn't have to be a red LED.  You have your semiconducting material embedded in the lamp.   Okay, so we have LEDs.  They work a little bit differently.  Does anyone have an LED? At home? [audience murmurs responses] Okay.  There's a few folks.  How about an LED with you right now?  Okay, so there's people with LEDs.  Are there people with smartphones right now? Okay.  So, these exist, we have them. 

 There are many in this room at this moment.   So when we start to look at the lighting market, and this is from the US Department of Energy in 2012 based on their 2010 data.  This is annual electricity consumption in terawatt hours per year, broken down by sector.  And the focus today will be residential.  And residential, okay, so it's primarily, in 2010, incandescents.   Do you think that's changed?  Maybe?  [audience responds] So it has at some people's houses for sure.  And other people's houses, we'll talk about too.  But, overall, in 2010,  we used about 700 terawatt hours of electricity annually for lighting.  And although residential isn't the biggest sector, it's interesting because you're starting to deal with consumers and their individual behaviors.  Do you think people demand more light over time?  Maybe?  So, in 2001, the average number of sockets per household was 43. 

  Do you think that's gone up? - [Audience Member] Yeah.  So, as of 2010, the average is 51.  And that's one way of consuming more light, that you have more light bulbs in your house.  Now, there's been some evolutions in technology too.  And this starts at 2011 and goes through 2016.  And we've got pictures of an incandescent and a CFL and an LED.  And these are residential screw-in type replacements with a lumen output of about 800.  So, 60-watt bulb equivalents.  So we're comparing apples to apples mostly.   So, in 2011,  an LED was $33.90,  which seems like a lot for a light bulb. 

 And if we go to 2013, okay, we're at about $13, and today we're at about $4.50.  And incandescents have dropped a little bit.  There's some other factors at play that we'll talk about.  And CFLs have dropped a little bit too.  The energy consumption  has steadied for the conventional incandescent, and it's gone down a bit for an LED, going from 12 watts to about eight.  There's also a huge difference in the lifetimes of these bulbs.  So the lifetime of an incandescent is about 1,000 to 2,000 hours.   And a CFL?  About 8,000 to 12,000.   But an LED is about 25,000.  So, in theory, you could have a light bulb that lasts a really long time, even if it costs a little more. 

 And it should be more efficient to run because it consumes less energy.  So then everyone should buy them, right? No? Maybe?  So, we talked a little bit about the cost, and this is a chart looking at ownership cost.  So the ownership cost is the purchase price plus the use price normalized over the lifetime.  And, in this case, this is all in 2010 dollars.  And it looks at the ownership cost of light from 1800 to about 2011,  where we're transitioning from fire, which are things like candles, kerosene lamps, to incandescents, fluorescents, high intensity discharge, LEDs, and CFLs.   So the ownership cost has been going down, much like we saw in that one chart looking at the United Kingdom, where they were transitioning from gas and kerosene to electricity.   And there's some other factors at play also.  So, the Energy Independence and Security Act of 2007, who has heard of it?  Four people.  All right, we're doing well.  [audience laughing] Who has heard somewhere on television or the internet about someone trying to ban incandescent bulbs? All right, we're talking about the same thing. 

 So, the Energy Independence and Security Act of 2007 took effect between 2012 and 2014.  And it's not a ban, per se, on bulbs, but it requires increasing of the efficiency of incandescents.   So, if you look, we've got this EcoSmart box, and it says it's a better incandescent.  So it's formerly a 60-watt incandescent, and what they mean is it produces about 800 lumens.  But now it requires 43 watts,  so we've made an efficiency gain.  You also start to see things  like the lighting facts per bulb, which, does this remind anybody else of food labels? [audience laughing] That's why I'm like, calories of brightness.  So I can tell by looking at this, the brightness is about 800 lumens, so it's a 60-watt equivalent bulb.  And the energy used is about 13 watts, so it's probably a CFL.   Or it could be a really early LED.  And they rate the lifetime, and they say, okay, I'll use this for three hours a day, and it will last for nine years. 

 So it's a way of distilling information.   But here's the question, when you heard about the ban on bulbs, did anyone start ordering incandescents? [audience laughing] It's okay, two honest people.  All right.   So, this is David Brooks of Just Bulbs in Manhattan.  And I got this from the New York Times, where he's commenting that he has one customer who's ordering thousands and thousands of incandescents, because she never wants to be without them, and to please not tell her husband.  [audience laughing] So, he'll be surprised one day when he finds their storage unit of incandescent bulbs.  [audience laughing] But, So we have interesting behaviors that come about too that, I do not want a more energy efficient bulb, I'm going to use this incandescent forever.  Okay.  That's part of evolutions of technology.  So whenever I talk about CFLs, the question of mercury comes up. 

 Who here knows that a CFL has mercury?  All right.   How much mercury do you think?  So, I see some people saying a little bit.  So, it's about, currently they have about five milligrams of mercury per bulb.  And, okay, is that a lot? Is that a little? Should we care? There was one study that came out several years ago, where they said, okay, so there's five milligrams of mercury in the CFL, but it's more efficient than an incandescent.  So what if I look at the life cycle and I burn coal to make my incandescent, power my incandescent throughout the lifetime? Is that, how does the mercury balance work out? And if you move to the CFL even though it has mercury in it, you're saving mercury through the gains in efficiency.  So you're coming out ahead.  Now,  I've given talks similar to this enough times, that there are some good anecdotes that come up.   Who here has heard of Mercurochrome? [audience laughing] All right.  So, I was giving this talk once and I always, almost always, got attacked by someone for the mercury content in CFLs and they're terrible and they're going to kill us all and [muffled].  I was like, okay. 

 So that's what I was expecting.  And he comes up and he starts telling me that he doesn't think the mercury is a big deal.  Okay.  Good, someone's finally not attacking me over this.  And so then he tells me about something called Mercurochrome, which, help me if I'm wrong, is something at one point we used to dab on cuts to sort of clean them and heal them? I was like, oh, okay.  So then he proceeds to tell me that similar to our friend in New York hoarding the light bulbs, that he's hoarded Mercurochrome.  [audience laughing] And he has boxes and boxes full of this, that he still uses it today, mercury is not a big deal, and then he pulls out a bottle.  I was like, okay, I guess mercury isn't a big deal to everyone.  And that's a really great anecdote to keep next time I talk about this.  So, just a side note. 

  So one way to think about this, and I alluded to this a little bit when I was talking about the mercury in a CFL versus if you burned coal for the lifetime of incandescent.  So, something called life cycle assessment.  Has anyone heard of it?  Okay, three or four people in the back.  That's a good start.  So life cycle assessment is a systematic tool for looking at the environmental impact of a product or process throughout its lifetime.  So you're breaking it down into components like raw materials.  What's the environmental impact of my raw materials? What is the environmental impact of my manufacturing? What about the use phase? So in this case, when I take the light bulb home, I put it in the socket, I turn it on.  And what about end of life? What happens when it's done? So there's some Coca-Cola bottles on this slide, and that's because the first documented life cycle assessment was actually done by the Coca-Cola Company, I believe in the 1960s.   And they were curious about the energy consumption for their packaging, because energy means money.  And they wanted to know what kind of packaging should I use? What should I put my soda in? Or I could say pop because I'm from Michigan. 

  And so the study results were never released, but that's sort of what we herald as the first life cycle assessment.   So, to put that in perspective, we can look at one.  This is from the US Department of Energy for an incandescent light bulb.  And I've got the electricity generation mix on the side, because that's a valid point in this.  And, okay, so you have your materials and manufacturing, it's a very small part of the life cycle environmental impact.  And the really big part is the use phase.  So when you take your light bulb home and you use it.  And on the bottom we've got all of these categories.  So you see things like global warming.  And global warming, has anyone heard of an environmental footprint? Right, so these are different units to do. 

 So global warming, you're thinking about carbon dioxide emissions.  Nitrification you're worried about nitrogen.  And we like to look at a suite, because you might find that while something is very good in one category, it is very bad in another.  And you need to think about the environmental trade-offs.  So, it's long been established that the environmental impact for incandescent lighting is during the use phase.  So the question was, what about these new, more energy-efficient lights? They're more energy efficient, so they should have less use phase impact, but they require more raw materials.  So how does this balance out? So, we can look at a compact fluorescent, and the use phase is still dominant.  Although, some phases like non-carcinogenics, we start to see more in materials and manufacturing.  And the same is true when we start to think about light emitting diodes.  And in categories like non-carcinogenics, the bigger manufacturing and materials cost has to do with the heat syncs that go into making light emitting diodes. 

 But we're going to go back.  So we know the use phase is dominant, and we know the ownership cost has been going down, so it costs less to use these.   So, who's ever heard of William Stanley Jevons? All right, I got like three or four people again.  So, he is an economist from the 1800s,  and he was looking at coal.  And he said when the efficiency of coal usage increases, we're actually using more coal, which was this big revolutionary idea at the time.  And some people would say it's revolutionary today.  If it's more efficient, how are we consuming more? So who thinks we do?  Discounting the title of this talk, of energy efficiency and the rebound effect.   So, there was a study out of MIT, that looked at multiple industries  over multiple time periods and geographic scales.  And they said, okay, we can look at  the annual average change in efficiency.   So that's your delta E over E. 

 And we can look at the change in consumption.  And if the change in consumption is more than the change in efficiency, we're going to out-consume our benefits of efficiency.  So, if you look at the last column, with delta Q over Q and delta E over E,  all of the numbers are bigger than one, which means that over the time scales they looked at, we out-consumed all the benefits of efficiency from a consumption standpoint.   And they qualified this though.  They said in the short-term, you might see savings because increased consumption hasn't caught up with your increases in efficiency.  But on the long-term, we haven't seen this in any of these industries.  And they took a large spread of things like passenger air travel, motor vehicles, refrigeration.   So, one question would be, how do you consume more light? Do we buy more lights?  So, suddenly the cost of lighting has gone down, I'll buy more? I buy brighter lights.  This goes back to when we were talking about electric lighting in Chicago, where they were saying what had once seemed adequate for indoor lighting, suddenly seemed dim and dark and hopeless and depressing.  So let's have more light because we can have more light, and we think we need more light. 

 You could leave the lights on longer.  Maybe you never turn off your lights then, because they're efficient.  It's an extreme example, but it's possible.  And the more times I've given a talk like this, someone will say, no, I would never ever ever leave my lights on longer, never.  And then they'll start telling me that, you know, I bought this LED.  I'm like, great, you bought an LED.  And I decided to put in on my garage, and now I leave it on all night, because it's so cheap to run.  Okay.  Well, that goes back to our safety, to what is light.  And there's some utility of light that you can't really measure for lumens per watt. 

 It's what is safety, what is security?  So, there, this is results from a study that looked at how long do people leave their lights on.   And this is a national survey that looked at five or six major metropolitan areas.  So there's a spread.  The average is 8.9 hours per day plus or minus 5.1.   Okay.   And the most commonly occurring value was six.  However, if you look, there are people who leave their lights on one hour per day, and people who leave their lights on 24 hours per day.  So, looking at this, I would say the population is heterogeneous.   And I get nods.  So, they're different. 

  And we can look at questions.   This is a slightly older study.  So, what's the highest price you would pay for an LED? And at the time of the study, an LED was $33.99.   And most people said they would pay about $17.   Does anyone remember what we're at now? Right, about $4.50.  So, in theory, based on this, we should see people buying a lot more LEDs.  But populations are heterogeneous, people interpret things differently.  And this was a really interesting question from the survey, where we asked, we framed the same question three different ways, essentially.  And we called it light bulb A, light bulb B, and light bulb C.  So A is an incandescent, B is a CFL, and C is an LED. 

  So, we framed asking people, so it costs so many dollars and it lasts for so many hours, what would you pick? And then we asked the same question, it costs so much and it would cost you this much to run per year, which would you pick? And then we also said, okay, it costs this much to purchase, and for the same amount of money you could drive so many miles per year, which would you pick? So across all three, about half the respondents said they would pick option B, the CFL, and they didn't know it was a CFL.  I'm sure if they Googled it, they would have known it was the CFL.  But you see this movement between question 18, and then when you look at question 19 and 20 of, LED versus incandescent.  So there's some interesting issues of perception of what is efficient, what should I buy, how should we word things.   So, how should we model this?  Has anyone heard of an agent-based model? Maybe a social scientist out there?  So, agent-based modeling  has roots in the social sciences.  And it's a method commonly used to model individuals.   And it's really good at that, and it's been used to model things like fish, geese flying in a V, sheep, and people.  But there's more, those are just a few examples.  And the idea is you have all these individuals following some set of rules, seeking to maximize some utility, and what do they do.  So there's this question of, could we apply this to lighting? What do people do if they can pick energy efficient lighting? So the result is this nice chart for an agent-based model,  where you've got some population that we informed with our survey data, and if their bulb is burned out, they go and buy a new light bulb. 

 Okay, that's a good assumption.  If it burns out, I'll buy a new one.  They use some probabilistic utility to decide which light bulb based on the fact they're a heterogeneous population.  So, different people value things differently.  And then, if their bulb is more efficient, they have this question of, do they consumer more light? And I was informed with the survey data that some people will consume more light.  And the question of how much, is sort of this interesting tipping point we looked at.  So okay, we've got some sort of model.  What do we know about the data we put in the model? So, one question on the survey that went to this model, was your environmental mindfulness, or your environmental attitude.  How environmentally friendly do you think you are? Do you care?  And this is looking at statistically significant correlations, for people who thought they were extremely mindful.  And, okay, so they want to save energy. 

 They're concerned about environmental friendliness of what they buy.  They apparently were not that interested in the quality of light, or how long their light bulbs lasted, which I thought was interesting because you would worry about, well I'm throwing it out.  In the survey, more than 50% of the people threw them out and did not recycle.   Then we have our average mindfulness.  They're actually worried about the lifetime of the bulb.  So it's just interesting to think about the heterogeneity of the population.   And, okay, so one way you can think about making these agents in a model, is they were trying, how would they pick a light bulb? So, in order to use a probabilistic utility, the question was, what do you think is most important, when you pick a light bulb? Because we all go and buy a light bulb and we think about this internally, maybe not formally.  But there's trade-offs.  And so 36% of the respondents thought saving money as a result of increased efficiency was most important.  Only 12% ranked environmental friendliness as the first. 

 So yet again we have a spread of data.  We also said, would you use more if you adopted a more energy efficient light bulb? Which is crude and surveys are never perfect.  Every time I talk about something like this, people tell me surveys are never perfect.  And I say yes, they're not, I know.   So about 50% said they would use more light.  And we said, okay, well, how would we use more light? So, of that, 33% would leave current lights on longer, 31% would purchase more lights.  And you could do both.   So, we have this model.  We have some scenarios, predicated on the rebound effect or Jevons' paradox.  The idea that people will consume more. 

 So there's scenarios with varying degrees of, if you consume more, how much more light would you consume? Because the question is, when are you going to erode the savings gained by efficiency? So it varies from no rebound, and we have some spontaneous adoption where people say I don't care that my light bulb's not burned out.  This LED is so cool, I must go buy one right now, which happens.  We're all guilty of that sometimes with some things.  To scenario eight, which is extreme rebound.  If you buy a more energy efficient bulb and you're that 50% of the population, you will leave your lights on 75% longer and buy 75% more.   So, the results aren't that surprising.  We have our average annual household light consumption in mega lumen hours.  So, in the extreme scenarios, the respondent, you consume a lot more light.  You'd expect this.  So the question was really, what does energy consumption look like? And in the extreme scenarios, you consume a lot more energy, more energy than you were consuming initially. 

 So, what does this mean? So, this is comparing with some data from the US Department of Energy.  In their earlier studies, they didn't consider the rebound effect, but they did consider a 1.75% annual growth in lit spaces,  due to bigger houses and expansion of lit spaces.  So, this is comparing their data, the US DOE,  with the non-extreme rebound scenarios.  So, in the study we found that, okay, we can predict that energy consumption for light will drop a lot.  And then eventually it'll inch back up, which is what the paper by [muffled] out of MIT, that looked at all the sectors, said.  Unless we come up with something new, or we come up with a policy, we're eventually going to out-consume.  So this brings up an interesting question  called the saturation of light.  So what is the limit for light? Is it constant daylight? Everywhere, all the time, outside even? Is it light of a certain brightness?  Does the saturation for light in a room change depending on who's designing it? So we don't know.  And there was a paper a few years ago by Tsao et al, that said,  it was a controversial paper.  They got lots of comments. 

  That said using a Cobb-Douglas framework,  we don't think we've reached saturation of light anywhere in the world.  Okay.   So, going on that, there's this question of, what is saturation of light? What does it look like? But there's this question because LEDs are an enabling technology.  So what if we start using light and lighting, for things we never have before? Or what if we start using bigger things we haven't thought of? So this is looking at television screens.   So the new flat screens commonly have LEDs or all LEDs.   TV screens are getting bigger.   In 2015,  52% of television sales were between 40 and 49 inches, and 20% was greater than 49 inches.  So, it's an enabling technology, we can make bigger televisions.  We're consuming in ways we hadn't thought.  What about this?  Does anyone recognize this?  So, County Stadium  and circa 1950s, I believe. 

  So this is a scoreboard.   And County Stadium no longer exists.  But does the scoreboard in Miller Park look like this? No.  So, okay, this might have had some light, but it's not some brightly lit television display.  And here we go.  This is a scoreboard at Miller Park.  And we've got this black and orange lighting.   And what about today? We seem to have caught Clay Matthews.  So we're using light in ways we wouldn't have thought to in the past.  If you would ask someone in the 1950s, is this the scoreboard of the future, I don't know that they would have known. 

 So it's hard to come up with a saturation for light and a limit, if we have all these new ways to use it.  And another example is a book.   So, Silent Spring by Rachel Carson, a very famous book credited with the environmental movement, talking about the dangers of chemicals, which isn't really a topic of this.  But, okay, is this the only way to read books today?  No.   All right.  So this is the first Kindle  in, I believe, 2007.   So only 11 years ago.   And both of these are not backlit, you need light, but light comes from external sources, like for illumination in the room.  But then we go to something like the Kindle Fire, which you can buy today, or many people probably bought on Prime Day yesterday.  And you still need light, but you've got this backlit screen. 

 So we're using light in new ways that we haven't thought of before.  And I mentioned that LED is an enabling technology and novelties.  So we're using ways, we're lighting things that we wouldn't have lit before also.  So we've got LED screens, but how about some pretend candles that change color? Or light-up glasses? Or rope lighting, which, on the way in, someone told me they bought for their garage.  Or what about a light-up shower? You can buy it with an LED.  And light-up balloons and snuggly children's nightlights that don't get hot.   So, it's hard to come up with this saturation of light if we have all of these new enabled technologies coming about.   So just to think about conclusions a little bit.  Historically, artificial light has been about more than just illumination.  It's progress. 

 It's wealth.  It's a status symbol.   And there's a potential to save energy, if we adopt energy efficient technology for a while.  But eventually they either need to come up with a policy, or we need to come up with a more efficient technology, if we're considering the rebound effect.  What is the saturation of light? That's a good question.  It depends what we're coming up with next.  And there are many novel uses of light, from children's toys to light-up showers, which I don't have.  But, maybe someone does and that'd be very exciting.  So, with that, I need to thank the University of Illinois Institute for Environmental Science and Policy, and the Civil and Environmental Engineering Department, here at the University of Wisconsin, Madison.  And I enjoy this for questions. 

  [audience applauding]