How long does a plant need its MDR of light?

[chopster01]

Lighting requirements still mystify me—the more I read, sometimes the more confused I get . I am especially confused about how the requirements listed for particular plants relate to the intensity/duration of a light source. For example, if a plant is listed as requiring 2000-3000 fc, how long must it receive the minimum 2000 fc to thrive? Four hours? Eight hours? Twelve hours? I have plants both in windows and under lights and the question seems pertinent to both, if for slightly different reasons.

I have two east facing windows. Depending on the time of day, I can get high readings of 3000 fc and even 5000 fc for short periods, which then fall off rapidly after noon to below 400 fc. If I take an average of light intensity to determine which plants I can grow, should I take it over four hours, eight hours, or twelve hours (or more) to determine if I can grow medium light varieties as well as Paphs, Phals, and an occasionally Encyclia? In other words, over how long of a period does a plant need to receive its minimum daily requirement of light?

The same question would apply to my western windows, which I am exploring the possibility of filling with plants as well—never to see the outside world again!

Fluorescents put a different spin on the same question. I have a bank of 4 T8 lights that I currently keep on for 16 hours a day. Depending on placement, plants could receive anywhere from 500 fc to around 1000 fc a couple of inches from the tubes. These are just the minimum requirements for Paphs and Phals, yet people on the boards claim they flower higher-light varieties like Tolumnias, Neofinetia, and even Oncidiums under T8s. So duration must have some sort of positive impact on intensity. How do you calculate that?

I am considering ordering a Hydrofarm four-lamp T5 fixture. Though less expensive on ebay, it is still considerably more expensive than the T8 setup. Yet one member claims he only gets 1800 fc two-three inches from his T5 setup. While this is slightly less than double the light put out by the T8 setup, it is hard for me to believe that the expense would be worth it unless the T5 lights enable you to grow higher-light plants than the 1800fc figure might indicate. And if duration does elevate that figure to higher levels, say to 2500fc so your oncidiums thrive, how much distance would be necessary so you can keep your lower light varieties from burning up (an important consideration when building a setup).

I know you are probably bone-tired answering these questions—over and over and over. But I haven’t quite got it yet, so please be patent with me and help me out if you can.

Thanks,
Charlie

[Ross]

Originally Posted by chopster01

Lighting requirements still mystify me—the more I read, sometimes the more confused I get . I am especially confused about how the requirements listed for particular plants relate to the intensity/duration of a light source. For example, if a plant is listed as requiring 2000-3000 fc, how long must it receive the minimum 2000 fc to thrive? Four hours? Eight hours? Twelve hours? I have plants both in windows and under lights and the question seems pertinent to both, if for slightly different reasons.

I have two east facing windows. Depending on the time of day, I can get high readings of 3000 fc and even 5000 fc for short periods, which then fall off rapidly after noon to below 400 fc. If I take an average of light intensity to determine which plants I can grow, should I take it over four hours, eight hours, or twelve hours (or more) to determine if I can grow medium light varieties as well as Paphs, Phals, and an occasionally Encyclia? In other words, over how long of a period does a plant need to receive its minimum daily requirement of light?

The same question would apply to my western windows, which I am exploring the possibility of filling with plants as well—never to see the outside world again!

Fluorescents put a different spin on the same question. I have a bank of 4 T8 lights that I currently keep on for 16 hours a day. Depending on placement, plants could receive anywhere from 500 fc to around 1000 fc a couple of inches from the tubes. These are just the minimum requirements for Paphs and Phals, yet people on the boards claim they flower higher-light varieties like Tolumnias, Neofinetia, and even Oncidiums under T8s. So duration must have some sort of positive impact on intensity. How do you calculate that?

I am considering ordering a Hydrofarm four-lamp T5 fixture. Though less expensive on ebay, it is still considerably more expensive than the T8 setup. Yet one member claims he only gets 1800 fc two-three inches from his T5 setup. While this is slightly less than double the light put out by the T8 setup, it is hard for me to believe that the expense would be worth it unless the T5 lights enable you to grow higher-light plants than the 1800fc figure might indicate. And if duration does elevate that figure to higher levels, say to 2500fc so your oncidiums thrive, how much distance would be necessary so you can keep your lower light varieties from burning up (an important consideration when building a setup).

I know you are probably bone-tired answering these questions—over and over and over. But I haven’t quite got it yet, so please be patent with me and help me out if you can.

Thanks,
Charlie

Charlie, some of this has been addressed earlier, but the short answer to the whole issue(s) is a decent light meter and lots of experience. I have been doing this for some time, now and delt with just about all this and come to some conclusions (for me):

1) The photoperiod for a plant is a much contested topic. There will be those that jump in here and claim the darkness period means nothing (my words, not theirs). There are thos, like me, that have found (perhaps by chance) that a change in "day length" (lights on period) from shorter in winter (northern hemisphere) to longer in summer seems to stimulate flowering. I have too many successes and examples to believe otherwise.

2) You are asking the right question, when you are trying to figure out the relationship between 12 hours constant light output as compared to a 12 hour day that starts out at dim light (dawn) moves on to highest light (usually mid day) then on to dim light again (dusk/twilight). This scenario is true for nature and in a greenhouse that does not have supplemental lighting. I've never seen a discussion, backed up with evidence, of a way to calculate or translate those requirements you are curious about. My "gut feeling" based on direct observation, is that you can place a Brassavola nodosa that was kept under near sunlight in a greenhouse, under a t5 setup like mine for 14 hours at 1800-2000 foot candles and watch all the leaves turn bright red-purple. Then after a few weeks the coloration turns back to light green. This can only happen when the light accumulation within the leaves is near the maximum the plant can sustain. Beyond that observation, I doubt you'll find anything constructive to answer your question. Suffice it to say, the staedy light output does equal a much higher lightsource that dwindles over the day. The same thing may be true about "light movers" with HID lights, but I don't know that.

3) t5 lights put out way more light than you suggest. Right now my 4-tube, 48" fixture measures between 1800 and 2000 foot candles at probably 6-8". The light fixture sits 4" above the orchidarium. I am still measuring at least 800 foot candles near the bottom of the tank (28"). All this is a function of the quality of the tubes you select and the quality of the fixture/reflectors. I used a Sunblaze system for a while and got much lower readings. Some of these were reported on this board. I was not happy with this at all so switched to a New Wave system New Wave T5 High Output Fluorescents, a grow light for plant propagation / cloning and seedlings at Sunburst Hydroponics and the output increased dramatically. With the other system, the fixture sat directly upon the top of the tanks and the plants closest to it had gotten accustomed to the levels (don't recall what I read at that time.) When I switched, the New Wave fixture also sat on the top of the tank and the same plants started turning red over the next couple weeks. I have since adjusted the lights higher to lessen the total foot-candles at the plant.

The window questions are also valid. Without supplemental lighting, you are getting exactly as you measure. I see no reason why you can't average the amount of light over the number of hours such light exists. Obviously, in winter (northern latitudes) day length is shorter. In my situation I added compact florescent lights (because of space and design constraints) in a south-facing bay window. They are significantly weeker than full sun, but significantly stronger than gray-sky days at dawn and dusk. I use the same 12 hour - 14-16 hour day variation I use for my orchidarium.

Don't ever worry about asking questions here (even over-and-over) because we've all struggled (at some point) with these same issues. Once you get a few months to years of growing under lights "under your belt" you will feel more comfortable with the whole issue (even if you still haven't figured out the science. I haven't.) Now I hope some others like John will join in. There are a few with whole basement grow rooms (I mean big ones) that grow exclusively under lights and maybe can shed some.... (get ready for this ) light on the issue.

[chopster01]

Ross,

I got a meter (one that actually works). Now I'm gathering data.

About your T5 setup: It's very reasonably priced since it comes with bulbs included. I was wondering what the distance is from the top of the v-hooks holding your lamp to the bottom of your orchidarium. I mean, what's the total vertical space occupied by your set-up: hooks, lamp, and orchidarium? I have fixed shelving that might accommodate a setup. Otherwise, I will have to rig up something new.

As to finding out what I can grow with my existing window and lights situation, looks like there's lots of data-gathering ahead of me.

Charlie

[Ross]

Originally Posted by chopster01

Ross,

I got a meter (one that actually works). Now I'm gathering data.

About your T5 setup: It's very reasonably priced since it comes with bulbs included. I was wondering what the distance is from the top of the v-hooks holding your lamp to the bottom of your orchidarium. I mean, what's the total vertical space occupied by your set-up: hooks, lamp, and orchidarium? I have fixed shelving that might accommodate a setup. Otherwise, I will have to rig up something new.

As to finding out what I can grow with my existing window and lights situation, looks like there's lots of data-gathering ahead of me.

Charlie

Charlie, ceiling to shelf (cabinet top) supporting orchidarium is 58". FRom top of the V hooks to cabinet top is 43". The lights are on holders like these Plant Grow Light Hood Lift & Hanger System Hope this helps.

[chopster01]

I don't want to derail this discussion into another chin wag about fluorescent lighting. If anyone DOES have an equation or rule of thumb about duration/intensity that I could use until I gain a little more "feel" for things, please, please share it.

But... ;-)

Ross, I do have an area that might be suitable for a T5 setup. I won't be able to get quite the interval you have, but I could use it for higher light varieties.

However my fixed solid wood shelving where I now have my T8s does not allow sufficient interval between shelves for four T5s. Between the bulbs and the top of my humidity trays there's a max clearance of 16 inches (so even less between lamps and plants of course).

A question occurs: On each shelf I have two four-foot T8 shoplights (4 bulbs for each shelf). If I replaced the T8s on each shelf with one TWO-bulb 4-foot T5 fixture, would I gain much, if anything? And would it still be 'safe' for my lower light plants? Or should I just stick with the T8s for these shelves and think about the T5s for the other setup?

But no matter what I do, I still have to figure out how long plants need their minimum daily light requirements...

Also,what size cfls do you use for your supplemental lighting? What sort of fixtures do you use? Would those round aluminum reflector shop lamps with (usually orang or red) clamps on the end do the job?

[bh4bhwgm]

Ross, I really applaud you for the manner in which you answered Charlie about the lighting. I was puzzled by the same question about light. Thanks -you have set my mind at ease. King

[anitalenor]

I have an Easter lilly type stemed yellow spyder shaped had spots on them, & of corse died off after I brang it home. Now I have a hollowish stock stem,& a long skinny dried stem. I heard not to remove these...Thanks

[anitalenor]

Also using an old GE plant light(blue) to keep them healthy.
I tried to read how long ect. & what a challenge that was candle light? So I'm playing that one by ear, too. They're in the corner under light in l/rm & have grey skies through patio doors.
Any feed back will b appreicated! Thanks, the other 2 orchids are the raisin faces,no flowers since in home,& they have a hard stm where flower use to be. Keep or remove?

[Ross]

Originally Posted by chopster01

If I replaced the T8s on each shelf with one TWO-bulb 4-foot T5 fixture, would I gain much, if anything? And would it still be 'safe' for my lower light plants? Or should I just stick with the T8s for these shelves and think about the T5s for the other setup?

A short answer: if you were able to replace the t8s with t5s, yes you would get more foot candles. But the long answer is: you can't do that. The bulbs are not directly replaceable. The fixtures won't accept the newer bulbs, for one, and if they did, the ballasts would blow up!. I see where Lowes is now carrying t5 normal output (not high output) fixtures. This is a start to the ones we need for orchids.

If you were to replace the fixtures themselves, then yes, you would see a dramatic increase in light output - depending on the fixture. Dedicated t5 fixtures tend to yield very high light output per watt consummed. That's the t5 HO type fixtures and tubes.

[Magnus A]

Charlie, as Ross has given you great insight in the "light science" I have only some small comments.

My best advice is try try and try again. I have seen low light species grown under very high light and thrived and I have seen high light species bloomed under low light! Orchids seems to be the masters of adaptation. As long as you do not burn your leaf you can give enormous amount of light without problem, actually much more than is possibly under normal home conditions.

For the time interval I should suggest to give something around 13-15 hours of light. I agree with Ross that plants needs dark periods to prosper. For the amount of light give everything you can but do not buy a lot at this point. expand your light sources slowly and try to learn how your chids react.

To make the calculation you are asking for you need the variation of the light during the day. And that is never given in any source! Usually you have the maximum light at the native site and nothing more! As I wrote above, give 13-15 hours of light.

For everyone, Do not make light more complicated than it is. Do not try the scientific way to predict everything! It is far far to complicated and will not give you the answers, we deal with living things that react in ways we cant predict! You have to test and try and test again after evaluation. Give as much light you can and try to give day and night and everything will work out in the end.

/Magnus