Light levels for orchids.

[Ray]

Originally Posted by bil

Ray, can you expand on PAR and PPF please? I can get DLI and ppfd on this app

PAR - Photosynthetically Active Radiation - is simply referring to all the wavelengths between 400-700 nm.

PPF - Photosynthetic Photon Flux - is the rate at which photons in the PAR range are striking the plants. PPFD is the density of those, expressed in micromoles/square meter/second.

DLI - Daily Light Integral - is the sum of all PAR photons received over the course of a day, and that is probably the most important factor, and most universal, as it applies to any type of light source. Finding a reliable DLI range for orchids is difficult, unfortunately, but is improving.

Shadeflower’s last few paragraphs are a great, practical example of the concept.

A very rough conversion from sunlight foot-candles to PPFD is 0.200, meaning that a recommended 1500 FC would be equivalent to 300 micromoles/sq m/sec, but we cannot forget the fact that - again - that is the peak, noontime PPFD, and the Sun’s intensity goes from zero to max to zero over the course of the day.

If we take the average to be half that, then multiply by the time (12 hours are 43200 seconds), our DLI becomes 150 x 43200 = 6480000 micromoles, or 6.48 moles of photons.

So, I suppose that a very general way to convert (peak) FC recommendations to DLI would be FC x 4320 = DLI