LED Growlights 2021

[SimonT]

I have been using a Sansi 36w LED grow lights to extend day length for some seedlings growing on a windowsill over the winter. I have this setup so it should gives PPFD 200uM/s/m2 according to the information that comes with this light. This a fairly modest intensity of light on paper but seemed to be OK for Rebutia anyway. I even had to reduce the light level a bit for germination, otherwise the seedlings started to look a bit stressed. I'm just wondering how this compares to the light intensity used in these more extensive grow environments?

[KarlR]

I have been using a Sansi 36w LED grow lights to extend day length for some seedlings growing on a windowsill over the winter. I have this setup so it should gives PPFD 200uM/s/m2 according to the information that comes with this light. This a fairly modest intensity of light on paper but seemed to be OK for Rebutia anyway. I even had to reduce the light level a bit for germination, otherwise the seedlings started to look a bit stressed. I'm just wondering how this compares to the light intensity used in these more extensive grow environments?

It's difficult to measure uM/s/m2 with any accuracy in a home setup. The last time I tried, which was about seven years ago I found an approximation for my two 400W M-H bulbs (6400K, full spectrum) which I used then, but I cannot remember the result off the top of my head. After a bit of questionable math I think I found it to equate to an overcast day in Mexico. The total uM/s/m2 for the whole day of artificial light that is (16 hours). This was good enough to have adult Ariocarpus growing compact and flowering, but I would still see etiolation in some Rebutias and Lobivias.

I'm sure that light fixture is fine to keep them happy over winter if you just intend to give them a drop of water from time to time. They would more than likely have no problem being stored in a cool and dark place over winter so long as they were completely dry, so the Rebutias don't technically need the light to get by over winter so long as they are totally dormant. If the windowsill is in a heated room they may need a drop of water once or twice over winter just to tick them over, so the the light will help avoid etiolation, but I don't think the light will be sufficient to keep them growing without etiolating. More than enough to keep the seedlings growing though.

[SimonT]

It is only the seedlings I'm planning to grow through the winter- just to try to get them to a decent size over one growing season. I guess I'll give it a go and see what happens.