I like this one, could be very useful for my experiments:
Skillman, J.B. 2008. "Quantum yield variation across the three pathways of photosynthesis: not yet out of the dark", Journal of Experimental Botany, 59(7):1647–1661 doi:10.1093/jxb/ern029
http://jxb.oxfordjournals.org/content/59/7/1647.full

Quantum yield
http://en.wikipedia.org/wiki/Quantum_yield

As the light intensity increases, photosynthetic CO2 uptake also increases. The formula for irradiance (light intensity) is the number of photons per unite surface area per unite of time, or umol M-2 S-1 (PAR). Less than 10 percent of the PAR falling on a citrus leaf will reach the internal leaves has implications for canopy photosynthesis. Only the exterior leaves will achieve maximum rates of photosynthesis. The interior leaves receive much less light that is either transmitted through other leaves or passes through gaps in the canopy. Most of these gaps are not static, due to wind moving branches and leaves, together with the absorption and reflection of light by leaves and soil creates an irregular patchwork of highly variable irradiance with in the canopy. As stated above, in dense canopies interior leaves often receive less than 10 umol m-2 s-1 (PAR).
Millet (705-)

Flower buds spoted in January (post Sun Jan 30, 2011 10:54 am) survived harsh over-wintering conditions and will open soon.

Acclimation is very important:
both ways: for end of season and for begin of season
and two fold: for light and for heat

My basic setup, photo 2011-04-09



Other things noticeable in the front, placed below pot when needed:
plate filled with dry sand (or a towel) for better drainage of WPT (water perched table)
wooden parts for faster pot heating

Similarly, high cover helping acclimation of experimental Siscia lemon graft owerwintered under LowLight and ExtremalLowTemp conditions,
photo 2011-03-15



Full cover over night.
High cover material has been replaced with shading net couple of weeks later...
More about experiment here
link

So you say that all of those trees were in full darkness during winter time?

Full darkness is again one big queston , YES or NO ...

When Dr. sc. Nikola Ljubešić was here last summer, he had a PAR instrument so we took some meassurements.

Datetime: 2011-09-06 11:20
High clouds were present, open sky: 1000 PAR.
For purpose here, it is safe to assume max PAR for clear sky to be 1800.

North window of the tool room, outside: 120
Inside the tool room:
0.2 m from north window: 45
0.5 m from north window: 25
1.0 m from north window: 10
2.0 m from north window: 5

Above means that my citrus trees, while kept in the tool room over winter, have only a single digit PAR available, most of the time.
What should not be forgotten is that LowLight condition comes in the pair, i.e. with LowHeat. This winter an average daytime temp there was often below 4 C, pots were even partially frozen mid February. No WLD (Winter_Leaf_Drop) occured.

Her Majesty, the Coldness, is on retreat now, toward summer residency in High Arctic.
My citrus forces are ready, waiting to run out and reclaim garden area.

Recon on duty:

Well done, keep us posted.

Normal PAR on cloudless (Full sunny day) is 2000. - Millet (311 BO-)

so I have about 12 citrus in the ground in my zone 5/6 (massachusetts)
They are all in total darkness from dec to whenever it warms up which is now (80's today). I just picked about 20 thomasville citraquats that ripened over the winter in the dark on the trees.
I have kumquats, meyers, satsumas , 10 degree tang, thomasveille and a few others..................so far so good

if I stare at the trees long enough they almost look like some have new leafs starting to bud!!

Hi,

I've started an experiment with two citrus plants which I'll overwintering them in full darkness. On right it's an Aurantium seedling and on the left it's a Tahiti Lime on Aurantium rootstock grafted in this summer. Here is a photo with the condition of plants after 2 weeks of staying in a closed box:


The temperature is between -2C and 6C degrees (28.4F & 42.8F). I'll keep you udated after every 2 weeks.

wow super , I did a test myself in the basement , after 4 months the leaves were blue-greenish in color but went ok , no leaf drop

where did you found those pots ?

Danero, many thanks for sharing this info! Good to know!
Here in our village there is a big nursery where they are selling ornamental plants, some of them exported from Italy. If I need a higher number of pots then I’m visiting this nursery and asking for used pots!
They have a huge warehouse with used pots where I can choose myself what I want and of course I got them for a song.

After 5 weeks in darkness:



In the last 3 weeks the temperature was between 1.2C & 12C (34.16F & 53.6F).