Micro-Naps for Plants: Flicking the Lights on and off Can Save Energy Without Hurting Indoor Agriculture Harvests
By Kevin M. Folta
A nighttime arrival at Amsterdam's Schiphol Airport flies you over the bright pink glow of vegetable production greenhouses. Growing crops under artificial light is gaining momentum, particularly in regions where produce prices can be high during seasons when sunlight is sparse.
The Netherlands is just one country that has rapidly adopted controlled-environment agriculture, where high-value specialty crops like herbs, fancy lettuces and tomatoes are produced in year-round illuminated greenhouses. Advocates suggest these completely enclosed buildings – or plant factories – could be a way to repurpose urban space, decrease food miles and provide local produce to city dwellers.
One of the central problems of this process is the high monetary cost of providing artificial light, usually via a combination of red and blue light-emitting diodes. Energy costs sometimes exceed 25% of the operational outlay. How can growers, particularly in the developing world, compete when the sun is free? Higher energy use also translates to more carbon emissions, rather than the decreased carbon footprint sustainably farmed plants can provide.
I've studied how light affects plant growth and development for over 30 years. I recently found myself wondering: Rather than growing plants under a repeating cycle of one day of light and one night of darkness, what if the same daylight was split into pulses lasting only hours, minutes or seconds?
Short Bursts of Light and Dark
So my colleagues and I designed an experiment. We'd apply the normal amount of light in total, just break it up over different chunks of time.
Of course plants depend on light for photosynthesis, the process that in nature uses the sun's energy to merge carbon dioxide and water into sugars that fuel plant metabolism. Light also directs growth and development through its signals about day and night, and monkeying with that information stream might have disastrous results.
That's because breaking something good into smaller bits sometimes creates new problems. Imagine how happy you'd be to receive a $100 bill – but not as thrilled with the equivalent 10,000 pennies. We suspected a plant's internal clock wouldn't accept the same luminous currency when broken into smaller denominations.
And that's exactly what we demonstrated in our experiments. Kale, turnip or beet seedlings exposed to cycles of 12 hours of light, 12 hours dark for four days grew normally, accumulating pigments and growing larger. When we decreased the frequency of light-dark cycles to 6 hours, 3 hours, 1 hour or 30 minutes, the plants revolted. We delivered the same amount of light, just applied in different-sized chunks, and the seedlings did not appreciate the treatment.
The same amount of light applied in shorter intervals over the day caused plants to grow more like they were in darkness. We suspect the light pulses conflicted with a plant's internal clock, and the seedlings had no idea what time of day it was. Stems stretched taller in an attempt to find more light, and processes like pigment production were put on hold.
But when we applied light in much, much shorter bursts, something remarkable happened. Plants grown under five-second on/off cycles appeared to be almost identical to those grown under the normal light/dark period. It's almost like the internal clock can't get started properly when sunrise comes every five seconds, so the plants don't seem to mind a day that is a few seconds long.
Just as we prepared to publish, undergraduate collaborator Paul Kusuma found that our discovery was not so novel. We soon realized we'd actually rediscovered something already known for 88 years. Scientists at the U.S. Department of Agriculture saw this same phenomenon in 1931 when they grew plants under light pulses of various durations. Their work in mature plants matches what we observed in seedlings with remarkable similarity.
A 1931 study by Garner and Allard tracked the growth of Yellow Cosmos flowers under light pulses of various durations.
J. Agri. Res. 42: National Agricultural Library, Agricultural Research Service, U.S. Department of Agriculture., CC BY-ND
Not only was all of this a retread of an old idea, but pulses of light do not save any energy. Five seconds on and off uses the same amount of energy as the lights being on for 12 hours; the lights are still on for half the day.
But what would happen if we extended the dark period? Five seconds on. Six seconds off. Or 10 seconds off. Or 20 seconds off. Maybe 80 seconds off? They didn't try that in 1931.
Building in Extra Downtime
It turns out that the plants don't mind a little downtime. After applying light for five seconds to activate photosynthesis and biological processes like pigment accumulation, we turned the light off for 10, or sometimes 20 seconds. Under these extended dark periods, the seedlings grew just as well as they had when the light and dark periods were equal. If this could be done on the scale of an indoor farm, it might translate to a significant energy savings, at least 30% and maybe more.
Recent yet-to-be published work in our lab has shown that the same concept works in leaf lettuces; they also don't mind an extended dark time between pulses. In some cases, the lettuces are green instead of purple and have larger leaves. That means a grower can produce a diversity of products, and with higher marketable product weight, by turning the lights off.
One variety of lettuce grew purple when given a 10-second dark period. They look similar to those grown with a five-second dark period, yet use 33% less energy. Extending the dark period to 20 seconds yielded green plants with more biomass.
J. Feng, K. Folta
Learning that plants can be grown under bursts of light rather than continuous illumination provides a way to potentially trim the expensive energy budget of indoor agriculture. More fresh vegetables could be grown with less energy, making the process more sustainable. My colleagues and I think this innovation could ultimately help drive new business and feed more people – and do so with less environmental impact.
Kevin M. Folta is a professor of horticultural sciences and plant molecular and cellular biology at the University of Florida.
Disclosure statement: Kevin M. Folta received funding from the United States Department of Agriculture National Institute of Food and Agriculture and Vindara Inc to work on questions in agricultural lighting. He is affiliated with Eggsotics Eggs and Produce where his family grows some direct-market produce under hydroponic and/or artificial light conditions. He is reimbursed for travel related to talks in research and science communication. A full list of prior research funding may be seen at www.kevinfolta.com/transparency.
Reposted with permission from our media associate The Conversation.
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When hurricanes and other extreme storms unleash downpours like Tropical Storm Beta has been doing in the South, the floodwater doesn't always stay within the government's flood risk zones.
New research suggests that nearly twice as many properties are at risk from a 100-year flood today than the Federal Emergency Management Agency's flood maps indicate.
Flooding Outside the Zones<p>About <a href="https://furmancenter.org/files/Floodplain_PopulationBrief_12DEC2017.pdf" target="_blank">15 million</a> Americans live in FEMA's current 100-year flood zones. The designation warns them that their properties face a 1% risk of flooding in any given year. They must obtain flood insurance if they want a federally ensured loan – insurance that helps them recover from flooding.</p><p>In Greater Houston, however, <a href="https://doi.org/10.1111/j.1539-6924.2012.01840.x" target="_blank">47% of claims</a> made to FEMA across three decades before Hurricane Harvey were outside of the 100-year flood zones. Harris County, recognizing that FEMA flood maps don't capture the full risk, now <a href="https://www.hcfcd.org/floodinsurance" target="_blank" rel="noopener noreferrer">recommends that every household</a> in Houston and the rest of the county have flood insurance.</p><p>New risk models point to a similar conclusion: Flood risk in these areas outstrips expectations in the current FEMA flood maps.</p><p>One of those models, from the <a href="https://firststreet.org/flood-lab/research/2020-national-flood-risk-assessment-highlights/" target="_blank">First Street Foundation</a>, estimates that the number of properties at risk in a 100-year storm is 1.7 times higher than the FEMA maps suggest. Other <a href="https://doi.org/10.1088/1748-9326/aaac65" target="_blank" rel="noopener noreferrer">researchers</a> find an even higher margin, with 2.6 to 3.1 times more people exposed to serious flooding in a 100-year storm than FEMA estimates.</p>
What FEMA’s Flood Maps Miss<p>Understanding why areas outside the 100-year flood zones are flooding more often than the FEMA maps suggest involves larger social and environmental issues. Three reasons stand out.</p><p>First, some places rely on relatively old FEMA maps that don't account for recent urbanization.</p><p>Urbanization matters because impervious surfaces – think pavement and buildings – are not effective sponges like natural landscapes can be. Moreover, the process for updating floodplain maps is locally variable and can take years to complete. Famously, New York City was updating its maps when Hurricane Sandy hit in 2012 but hadn't finished, meaning flood maps in effect <a href="https://projects.propublica.org/nyc-flood/" target="_blank">were from 1983</a>. FEMA is required to assess whether updates are needed every five years, but the <a href="https://www.fema.gov/cis/nation.html" target="_blank" rel="noopener noreferrer">majority of maps</a> <a href="https://www.oig.dhs.gov/sites/default/files/assets/2017/OIG-17-110-Sep17.pdf" target="_blank" rel="noopener noreferrer">are older</a>.</p><p>Second, binary thinking can lead people to an underaccounting of risk, and that can mean communities fail to take steps that could protect a neighborhood from flooding. The logic goes: if I'm not in the 100-year floodplain, then I'm not at risk. Risk perception <a href="https://doi.org/10.1088/1748-9326/ab195a" target="_blank" rel="noopener noreferrer">research</a> backs this up. FEMA-delineated flood zones are the major factor shaping flood mitigation behaviors.</p><p>Third, the era of climate change scuttles conventional assumptions.</p><p>As the planet warms, extreme storms are becoming <a href="https://nca2018.globalchange.gov/" target="_blank">more common and severe</a>. If greenhouse gas emissions continue to increase at a high rate, computer models suggest that the chances of a severe storm dropping 20 inches of rain on Texas in any given year will increase from about 1% at the end of the last century to 18% at the end of this one, a chance of <a href="https://doi.org/10.1073/pnas.1716222114" target="_blank" rel="noopener noreferrer">once every 5.5 years</a>. So far, <a href="https://www.rstreet.org/wp-content/uploads/2020/02/195.pdf" target="_blank" rel="noopener noreferrer">FEMA hasn't taken into account the impact climate change is having</a> on extreme weather and sea level rise.</p>
Racial Disparities in Flooding Outside the Zones<p>So, who is at risk?</p><p>Years of research and evidence from storms have highlighted social inequalities in areas with a high risk of flooding. But most local governments have less understanding of the social and demographic composition of communities that experience flood impacts outside of flood zones.</p><p>In analyzing the damage from Hurricane Harvey in the Houston area, I found that <a href="https://doi.org/10.1088/1748-9326/aba0fe" target="_blank">Black and Hispanic residents disproportionately experienced flooding</a> in areas beyond FEMA's 100-year flood zones.</p><p>With the majority of flooding from Hurricane Harvey occurring outside of 100-year flood zones, this meant that the overall impact of Harvey was racially unequal too.</p><p>Research into where flooding occurs in Baltimore, Chicago and Phoenix points to some of the potential causes. <a href="https://www.nap.edu/read/25381/chapter/4#16" target="_blank" rel="noopener noreferrer">In Baltimore and Chicago</a>, for example, aging storm and sewer infrastructure, poor construction and insufficient efforts to mitigate flooding are part of the flooding problem in some predominantly Black neighborhoods.</p>
What Can Be Done About It<p>Better accounting for those three reasons could substantively improve risk assessments and help cities prioritize infrastructure improvements and flood mitigation projects in these at-risk neighborhoods.</p><p>For example, First Street Foundation's risk maps account for <a href="https://firststreet.org/flood-lab/research/flood-model-methodology_overview/" target="_blank">climate change</a> and present <a href="https://floodfactor.com/" target="_blank" rel="noopener noreferrer">ratings</a> on a scale from 1 to 10. FEMA, which works with communities to update flood maps, is <a href="https://www.fema.gov/media-library-data/1521054297905-ca85d066dddb84c975b165db653c9049/TMAC_2017_Annual_Report_Final508(v8)_03-12-2018.pdf" target="_blank" rel="noopener noreferrer">exploring rating systems</a>. And the National Academies of Sciences, Engineering and Medicine recently <a href="https://www.nationalacademies.org/news/2019/03/new-report-calls-for-different-approaches-to-predict-and-understand-urban-flooding" target="_blank" rel="noopener noreferrer">called for a new generation of flood maps</a> that takes climate change into account.</p><p>Including recent urbanization in those assessments will matter too, especially in fast-growing cities like Houston, where <a href="https://authors.elsevier.com/a/1boBRyDvMFW6W" target="_blank" rel="noopener noreferrer">386 new square miles</a> of impervious surfaces were created in the last 20 years. That's greater than the land area of New York City. New construction in one area can also <a href="https://scalawagmagazine.org/2018/01/city-in-a-swamp-as-houston-booms-its-flood-problems-are-only-getting-worse/" target="_blank" rel="noopener noreferrer">impact older neighborhoods downhill</a> during a flood, as some Houston communities discovered in Hurricane Harvey.</p><p>Improving risk assessments is needed not just to better prepare communities for major flood events, but also to prevent racial inequalities – in housing and beyond – from <a href="https://www.npr.org/2019/03/05/688786177/how-federal-disaster-money-favors-the-rich" target="_blank" rel="noopener noreferrer">growing</a> after the unequal impacts of disasters.</p>
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