PAR Expressed As DLI or Instantaneous? - The Planted Tank Forum
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post #1 of 7 (permalink) Old 04-15-2019, 12:32 AM Thread Starter
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PAR Expressed As DLI or Instantaneous?

Are the PAR values we use instantaneous readinds (umol/m2/s) or a daily light interval? If so, based on how many hours of light? I know in terrestrial growing we use instaneous values of around 600 umol/m2/s for optimal growth.
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post #2 of 7 (permalink) Old 04-15-2019, 01:26 AM
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Instantaneous..You need to do your own DLI calculation..
W/ out ramping it's pretty easy..
Quote:
Here is the formula for calculating DLI with a quantum meter.

μmol m-2s-1 x (,3600 x photoperiod) / 1,000,000 = DLI.
- μmol m-2s-1 is a reading, or averaged readings, from the quantum meter.
- 3,600 is the number of seconds in an hour.
- Photoperiod is the period (in hours) of light exposure per 24 hours.
BTW "PAR" isn't the correct term.. it's PPFD..
"PAR" has no time nor area component..
But that's a personal thing..

Quote:
PAR is photosynthetic active radiation. PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis (Figure 1). PAR is a much used (and often misused) term related to horticulture lighting. PAR is NOT a measurement or “metric” like feet, inches or kilos. Rather, it defines the type of light needed to support photosynthesis.
https://fluence.science/science/par-ppf-ppfd-dli/
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post #3 of 7 (permalink) Old 04-15-2019, 02:32 AM Thread Starter
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Thanks, but it's odd that 80 ppfd is considered "high." My grow room is in the 600ish range! Everything I read here says simply PAR so I wasnt sure if it was ppfd or a DLI value.

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Originally Posted by jeffkrol View Post
Instantaneous..You need to do your own DLI calculation..
W/ out ramping it's pretty easy..
Quote:
Here is the formula for calculating DLI with a quantum meter.

μmol m-2s-1 x (,3600 x photoperiod) / 1,000,000 = DLI.
- μmol m-2s-1 is a reading, or averaged readings, from the quantum meter.
- 3,600 is the number of seconds in an hour.
- Photoperiod is the period (in hours) of light exposure per 24 hours.
BTW "PAR" isn't the correct term.. it's PPFD..
"PAR" has no time nor area component..
But that's a personal thing.. <a href="https://www.plantedtank.net/forums/images/smilie/icon_wink.gif" border="0" alt="" title="Wink" >:-)</a>

Quote:
PAR is photosynthetic active radiation. PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis (Figure 1). PAR is a much used (and often misused) term related to horticulture lighting. PAR is NOT a measurement or “metric” like feet, inches or kilos. Rather, it defines the type of light needed to support photosynthesis.
https://fluence.science/science/par-ppf-ppfd-dli/
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post #4 of 7 (permalink) Old 04-15-2019, 02:05 PM
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Consider most aquatics "shade" plants..

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post #5 of 7 (permalink) Old 04-15-2019, 04:32 PM
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Plants have evolved like humans to a light cycle. They need a period of rest to process the by products of photosynthesis. One can not make up for poor lighting with a extra long photo period. This will stress the plant and cause issues.
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post #6 of 7 (permalink) Old 04-15-2019, 04:52 PM
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Quote:
Originally Posted by EdWiser View Post
Plants have evolved like humans to a light cycle. They need a period of rest to process the by products of photosynthesis. One can not make up for poor lighting with a extra long photo period. This will stress the plant and cause issues.

Studies actually dis-agree, to a degree but weren't specific to aquatic plants.. so.. still a guess.
Your statement used to be my belief as well..


Currently it is more of an "it depends"....
https://www.researchgate.net/publica...ntinuous_light
Quote:
Greenhouse crop production frequently makes use of supplementary lighting to improve plant productivity in periods of the year when natural irradiance is low; on some occasions, continuous lighting is used ( Mortensen and Fjeld, 1998;Dodd et al., 2005;Pettersen et al., 2006;Velez-Ramirez et al., 2011). For example, in pot roses, extending the lighting period from 18 to 24 h per day shortened the time to flowering by 12% and the number of flowers increased by 34% ( Pettersen et al., 2007). ..



And certainly a "not recommended" since one would probably need to do continuous CO2 ect.
Respiration occurs constantly, in the light or the dark, so that isn't ever an issue .

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post #7 of 7 (permalink) Old 04-16-2019, 01:20 PM
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This also in the case of production green house sitting. Which is way different from a hobbyist aquarium.
If one increases plant growth to a point it will also cause algae growth. An fish donít like lights on 24/7 either.

If you want to rush a bunch of flowers out to be sold. You could do this.
An the plants would not be under this condition for a very long time. As is the case of someone doing this in an aquarium.
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