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Title: From physics to fixtures to food: current and potential LED efficacy

Abstract

Light-emitting diodes (LEDs) have enabled a historic increase in the conversion of electric energy to photons, but this is approaching a physical limit. The theoretical maximum efficiency occurs when all input energy is converted to energy in photosynthetic photons. Blue LEDs can be 93% efficient, phosphor-converted “whites” 76% efficient, and red LEDs 81% efficient. These improvements open new opportunities for horticultural lighting. Here we review (1) fundamental physics and efficiency of LEDs, (2) the current efficacy of LEDs, (3) the effect of spectral quality on crop yield, and (4) the potential efficacy of horticultural fixtures. Advances in the conversion of photons to yield can be achieved by optimization of spectral effects on plant morphology, which vary among species. Conversely, spectral effects on photosynthesis are remarkably similar across species, but the conventional definition of photosynthetic photons (400–700 nm) may need to be modified. The upper limit of LED fixture efficacy is determined by the LED package efficacy multiplied by four factors inherent to all fixtures: current droop, thermal droop, driver (power supply) inefficiencies, and optical losses. With current LED technology, the calculations indicate efficacy limits of 3.4 µmol J-1 for white + red fixtures, and 4.1 µmol J-1 for blue +more » red fixtures. Adding optical protection from water and high humidity reduces these values by ~10%. We describe tradeoffs between peak efficacy and cost.« less

Authors:
 [1]; ORCiD logo [2];  [1]
  1. Utah State Univ., Logan, UT (United States). Crop Physiology Lab.
  2. Solid State Lighting Services, Johnson City, TN (United States)
Publication Date:
Research Org.:
KeyLogic Systems, LLC, Morgantown, WV (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Building Technologies Office
OSTI Identifier:
1624037
Grant/Contract Number:  
FE0025912; 2018-51181- 28365; NNX17AJ31G
Resource Type:
Accepted Manuscript
Journal Name:
Horticulture Research
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 2662-6810
Publisher:
Oxford University Press
Country of Publication:
United States
Language:
English
Subject:
Plant Sciences; Genetics & Heredity; Agriculture

Citation Formats

Kusuma, Paul, Pattison, P. Morgan, and Bugbee, Bruce. From physics to fixtures to food: current and potential LED efficacy. United States: N. p., 2020. Web. doi:10.1038/s41438-020-0283-7.
Kusuma, Paul, Pattison, P. Morgan, & Bugbee, Bruce. From physics to fixtures to food: current and potential LED efficacy. United States. https://doi.org/10.1038/s41438-020-0283-7
Kusuma, Paul, Pattison, P. Morgan, and Bugbee, Bruce. Mon . "From physics to fixtures to food: current and potential LED efficacy". United States. https://doi.org/10.1038/s41438-020-0283-7. https://www.osti.gov/servlets/purl/1624037.
@article{osti_1624037,
title = {From physics to fixtures to food: current and potential LED efficacy},
author = {Kusuma, Paul and Pattison, P. Morgan and Bugbee, Bruce},
abstractNote = {Light-emitting diodes (LEDs) have enabled a historic increase in the conversion of electric energy to photons, but this is approaching a physical limit. The theoretical maximum efficiency occurs when all input energy is converted to energy in photosynthetic photons. Blue LEDs can be 93% efficient, phosphor-converted “whites” 76% efficient, and red LEDs 81% efficient. These improvements open new opportunities for horticultural lighting. Here we review (1) fundamental physics and efficiency of LEDs, (2) the current efficacy of LEDs, (3) the effect of spectral quality on crop yield, and (4) the potential efficacy of horticultural fixtures. Advances in the conversion of photons to yield can be achieved by optimization of spectral effects on plant morphology, which vary among species. Conversely, spectral effects on photosynthesis are remarkably similar across species, but the conventional definition of photosynthetic photons (400–700 nm) may need to be modified. The upper limit of LED fixture efficacy is determined by the LED package efficacy multiplied by four factors inherent to all fixtures: current droop, thermal droop, driver (power supply) inefficiencies, and optical losses. With current LED technology, the calculations indicate efficacy limits of 3.4 µmol J-1 for white + red fixtures, and 4.1 µmol J-1 for blue + red fixtures. Adding optical protection from water and high humidity reduces these values by ~10%. We describe tradeoffs between peak efficacy and cost.},
doi = {10.1038/s41438-020-0283-7},
journal = {Horticulture Research},
number = 1,
volume = 7,
place = {United States},
year = {2020},
month = {3}
}

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Figures / Tables:

Fig. 1 Fig. 1: The general relationship between color temperature on percent blue photons (left axis), and the effect of color temperature on photon efficacy (right axis). Exact values vary among manufacturers. Photon efficacy in this graph is presented at a junction temperature of 25°C and 150mA. The efficacy values will shiftmore » if these inputs are changed, see below« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.