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Review
. 2020 Mar 30:7:56.
doi: 10.1038/s41438-020-0283-7. eCollection 2020.

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

Paul Kusuma  1 , P Morgan Pattison  2 , Bruce Bugbee  1
Affiliations
Review

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

Paul Kusuma et al. Hortic Res. .
No abstract available

Keywords: Light responses; Photosynthesis.

PubMed Disclaimer

Conflict of interest statement

Conflict of interestThe authors declare that they have no conflict of interest.

Figures

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 shift if these inputs are changed, see below
Fig. 2
Fig. 2. Effects of drive current on photon efficacy at a junction temperature of 25 °C.
The dashed lines in this graph represent inadequate test data at low drive currents. However, low drive current (e.g., 65 mA) is used in LED fixtures. Blue photons have a lower theoretical maximum efficacy than red photons, based on Planck’s equation, which states that energy is inversely proportional to wavelength (E = hc/wavelength). Blue photons centered at 450nm can provide 3.76µmolJ−1, and red photons centered at 660nm can provide 5.52µmol J−1. This is more of a characteristic of the photons than of the LEDs that make them
Fig. 3
Fig. 3. Effects of junction temperature on photon efficacy.
Note that higher drive currents increase the junction temperature. The dashed lines in this graph represent temperatures below 25 °C, and therefore temperatures below ambient conditions. Reducing the temperature below ambient would be an energy requiring process
Fig. 4
Fig. 4. Historical, current, and projected LED package combination efficacy of a 20/80% ratio of blue and red LEDs.
This is a weighted average of the two LEDs. The figure constrains LED performance to specific current and temperature operating conditions as discussed above. In practice, the current technology point is not constrained to these conditions so it can be higher than what is shown in the figure
Fig. 5
Fig. 5. Example long-term depreciation of LEDs based on temperature.
LEDs will depreciate slower when operated at lower temperatures. Specific rates of depreciation for LEDs will depend on color, current operation, package type, and LED caliber as well as temperature. Colors on the graph represent temperature and not LED color
Fig. 6
Fig. 6. A suggested fixture for high efficacy.
The Y-axis assumes one watt of input power
See this image and copyright information in PMC

References

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