Good inexpensive light meter? Intensity/time?
 

I searched "light meter" on this forum but didn't come up with any real suggestions. Is there a decent light meter out there that won't send me to the poorhouse? Currently I'm using a handheld photographer's meter and converting f-stops to footcandles according to a chart found in the book "Understanding Orchids" and all over the web. But I'm a little suspicious of my findings.

Also, if I get a reading of, say, 1500 fc under lights, does the light value increase the longer the lights are on: say 1500@12 hrs, 2000@14 hrs., 2500@16hrs.? Something like that? If so, what's the real formula?

the footcandle level does not increase as the time passes. flourescents value go up for like 5 minutes as they "wake up" and then it stays the same. as for a good light meter i use my camera light meter and do the same thing as you do. i've done the light conversions so many times i have the chart memorized:blushing: .

As for the first question, you get what you pay for. I don't mean to suggest you spend lots of money, but there have been a couple sales going on here in the vendor area for supposedly good meters. I paid lots for mine and I am happy I did. It's extremely accurate.

As to the second question, the short answer is that gardening under light is not at all like gardening in nature or a greenhouse. Daylight is not the same. For instance, let's say your lights put out 1800 foot-candles at 10" (a really high amount) this is not the same as 1800 foot-candles measured in a greenhouse or out on the deck. The reason: dawn comes with really low light until, say, 10 AM when light levels increase. Then they continue to increase till, say 1200hrs or 1300hrs when the sun is at it's highest (in June in northern latitudes) then it continues to wane, till it reaches a low at sunset. On the other hand, your florescents, or HID or whatever, come on full strength at the on cycle, and continue like that till they go off at the off-cycle. The accumulated "light energy units" (whatever that is) is potentially more with the lights than with the natural situation. Many hydroponics folks will attest to this. The only way to control blooming and growth with hydroponics is with "day length" as well as temperature, where possible. This is why it is possible (I have done it) to cause Brassavola nodosa to develope extremely reddish foliage at only 1800 foot candles. It has since adapted and now has only the typical red tinge.

Dear Bonsai and Ross,

Maybe you both understand my second question and just have different answers, but most likely I have been unclear. I'll try again.

Let's say my lights put out 1500 fc, (lower-range light). Of course that is a continuous, nonvaried output level. This is the light level reccomended for Phals and some Paphs. I guess the question comes down to this: If I keep the lights on longer, for 16 hrs/day instead of 10-12 hours a day, could I grow more mid-range orchids under the same set of lights? MiniCats or some oncidiiums? Does duration affect the "footcandle value" (I'm making terms up now) of my light setup in any way, or is a 1500 fc setup forever and only a Phal and Paph setup, no matter how long the lights are on?

Charlie

Related P.S.

When a plant is commonly rated 500-1500 fc, does that mean 500-1500 fc for 4 hrs.? 8 hrs.? Longer?

I really don't have a clear answer. I suspect it's some of both. I do think you can edge towards the brighter species with that light level and duration. But I can't prove that. Certainly you can place the plants very close to the tubes which will yield a highr FC range.

In most cases that means max light (I feel) as in that is light level in nature or greenhouse. So I would feel comfortable with 1000-1200 FCs for 12 hours of high intensity light. I never go below 12 hours with my lights.

I did a bunch of research on the web and decided to buy a light meter that has an accuracy level of 2%, can measure up to 10,000 foot candles (as if anything I'll measure will be that high), is made for this specific purpose, and comes highly recommended. It was fairly inexpensive, and it comes with a one-year guarantee, so if I'm dissatisfied, I can return it. It should arrive in a few days and I can't wait to try it out. Here is a link to the specs if anyone is interested.

Charley's Greenhouse & Garden greenhouses supplies charlies kits hobby garden accessories orchids winter green house

Ross, your responses are so helpful. Everyone here must appreciate you a great deal. Thanks!