Daylight Integral ( eng. Daily Light Integral ), abbr. IDO ( eng. DLI ) - the amount of photosynthetically active radiation (PAR) that the plant receives during the day. It is a function of the light intensity (instant light: µmol · m −2 · s −1 ) and time (day). It is expressed as mole of light per square meter per day, that is, mol · m −2 · day −1 .
Units of measurement and calculation of IDO
Daylight integral is a measure of the amount of light received in a single day in a particular area or territory. Usually, the IDO is expressed in the amount of PAR substance ( mol ) of photons that fell on an area of one square meter (m -2 ) in one day (day -1 ) - mol · m −2 · day −1 . Thus, the IDO serves as a measure of the number of photons of the LIGHTS obtained in an area of one square meter during the day.
RDI is usually calculated by measuring the density of the photosynthetic light flux (born photosynthetic photon flux density, PPFD) in μmol · m −2 · s −1 and its change during the day. After measurements, it is possible to sum up the flux density during the day and estimate the value of the OID.
So for example, if the density of the photosynthetic light flux remains constant for 24 hours, then the IDD in mol · m −2 · day –1 can be calculated by a simple equation:
Where 86400 s = 1 day
1 mol = 1000 000 μmol
Another example is the total solar radiation obtained in one day per square meter, or W · m −2 . Depending on the nature of the study, the daylight integral may be more useful than data on the instantaneous value of the intensity of the incident light. IDO varies depending on geographic latitude, season and cloudiness, and ranges from 5-60 mol · m −2 · day- 1 for PAR. In greenhouses or growth chambers, the IDO value is usually significantly reduced, which may affect the ratio of shoots and roots, morphology and timing of flowering.
IDO average values
On a sunny winter day in middle latitudes, the plant receives about 9 moles of photons / day. If the sky is cloudy, then the IDO falls to 3 mol / day. On a sunny day in summer, the daylight integral is about 26 mol / day and 12 mol / day on an overcast day. Each plant species has an optimal for growth range of IDO values. Measuring the daylight integral during the growing season and comparing the results can help the gardener decide which plant species can grow in this area.
Examples of calculation:
- IDO (mol / m 2 / day) = average light intensity (µmol / m 2 / s) · time (in seconds) / 1,000,000
- IDO (mol / m 2 / day) = HEADLIGHTS · h · 3600 / 1.000.000
References
- Korczynski et al., 2002
- Bunnelle et al., 2005 and Ilias et al. 2005