Suggested ppfd and dli for starts is 150ppfd and 6.5dli. That works for most plants too tomato cucumber you name it.
But that’s 11" away from a set of four two foot T5s and only a cycle of 12/12.
It works perfectly, seedlings are lush, not discoloured yellow and purple or pale like if I go closer if a longer cycle.
Those who have lovely seedlings what’s your dli and ppfd if don’t mind me asking
All advice was to jam seedlings two inches from bulbs for 20 hours a day and that gives ridiculous figures and multiple posts asking why seedlings aren’t growing or turning yellow.
My starts do best 150ppfd but can raise up after a week to nearer your levels. 300ppfd is quite close to my fluorescents only suits non seedlings or again yellow xanthophyll and purple anthocyanins develop.
I’m fact I found that hypocotyls were green at 150pofd when germinating and over that developed photo quenching high ligh stress chems like anthocyanins again.
Interesting I can grow them in higher light but they aren’t as big or quick growing for a while then bam they shoot up which I’d assume is when the light level becomes optimum for that stage and it was stressed at that level till it had enough growth.
I think the limitations PPFD has a lot to do with the development of the root system. Of course leaf structures have to develop to enable the plant to absorb more photons. But in order for the seedling to survive during the early stage it depends on some absorption of H2O through the leaves. Thus keeping the humidity high during the early stage of growth is essential to faster development.
For those that use CO2 enhanced grow spaces DLI, I assume, is not a limited concern.
Also there are those that use 18 hour photoperiod and limiting DLI would also not be a concerning.
I would suppose the VPD would be the key metric to monitor.
FWIW, I grow autos and was up to ~400 PPFD/25 DLI on Day 3 above the soil this grow (I plant germ’d seeds in their final pot of soil). I think step one is having a relatively proper temp/RH in order to provide proper lighting:
