Rosie,
I agree with you...
I just think the majority of the orchids that are grown by orchid lovers are from the tropics. Cattleyas, Dendrobiums, Phals etc etc.
Even many cool growing ones come from the tropics just high elevation...

I hope i do not sound pedantic, but I am just thinking plants from teh tropics are not used to shorter winter days. Then 2 hour difference of a few fluorescent tubes may be negligible. maybe equivalent to 15 / 20 / 30 min of sunlight.[/QUOTE]

The actual issure if your are talking about initiation of bloom by day lenght is actually the lenght of the dark period between the light periods... at least to my understanding. Could be there are some that do the oppisit also But most need the dark period to be right not so much the lenght of the day

Thay call plants short day for ones that actually need longer dark periods to bloom and long day for plants that need only a short dark period.

The actualy trigger is a chemical that builds up during light periods and needs a certan time in the dark for this chemical to revert to its original form. The dark period being to short will not let it fall below the level that triggers blooming...but is the reverse for short day plants they need a high level to trigger bloom

Not saying anything about the tropics and their day to night ratios just explaing the trigger for plants that do use this method a little bit and all plants do not nessecarrly use this method some depend of dry and wet seasons instead in fact. But thinking on it a decidious tree loosing its leaves could in fact change the light to dark period some....

I fully understand both sides concerning the change in light for tropical orchids (a very opinionated and debatable subject). I would imagine (although I am no expert) that it would be highly specific the genera (location, habitat, microclimate, etc). The reason I am going to bump down the light in the winter is because I also grow several temperate terrestrials (european and american goodyeras). Although the light change may not help the paphs, I am hoping it will help the others to recognize a "change in season" so to speak. So the paphs will have to adjust. I have read of other people growing them this way though so they should be just fine.

"Why bump down for the winter? actually you may need more. If you grow orchids that originate in the tropics it is usually about 12 day / 12 night hours all year around . You may need more light in the winter because you get less natural light from the windows..."

I thank you for the advice, but my grow space is in a room with only one, fairly small window, and it is on the opposite side of the room. Therefore, the amount of "natural light" that the plants recieve is pretty much negligable I would imagine. Given the advice of everyone that has contributed here, I may compromise and just bump down to 14 for the winter and go back to 16 in the summer.

I keep my lights on 18 hours, but does it matter which type of lights you are using?

I think it matters.
a battery operated flashlight is not as powerful as an halogen 200 W. T12 fluorescents are not as bright as dedicated T5 grow lights....

If you really want to get down to it look up the latitude of where the plant is from and you usally can find the average light they have for each month on the net ,sunrise to sun set.

@stefpix when you put it that way you are totally right

I would also not be too trusting on your light-meter.
Lights with interrupted spectrums like fluorescents or gas discharge lamps can give inaccurate readings on some light meters. :You might want to read this web site BluuGnome.com - Light Meters vs. The Human Eye. You will probably find you have the correct light. Just watch you plants.