footcandles emitted by one T5 tube - Orchid Board

ladyslipper · #1 (**permalink**) 10-12-2008, 02:48 AM

Hello, could anyone tell me how many foot candles does one 48 inch T5 tube emit? I believe I need to have 2000 FC for my Paphs & Phrags.

Thanks m

lambelkip · #2 (**permalink**) 10-12-2008, 01:39 PM

it depends on the wattage of the light, and the distance between the light and the plant. a higher wattage light will put out more light, but the light decreases as you move farther from it. see this post: Measuring light levels with an slr camera Paphs need about 1000fcs, not 2000

mayres · #3 (**permalink**) 10-12-2008, 01:50 PM

T5 (and other lights) are measured in lumens not footcandles in terms of how much light they emit. This is in reference to the TOTAL amount of light emitted 360 degrees around the tube and the full length. My T5 tubes emit 5000 lumens. As noted above, the footcandles is the intensity of the available light striking your object/plants - which decreases as you increase the distance from the tube AND also keep in mind that all of the available light from the tube is not directed towards your plant(s). Some of it is lighting up your room and going to "waste".
A camera will work as noted to measure the footcandles and a good inexpensive light meter is even better IMHO - you can find them at places like ebay for as little as $20.
A T5 fixture will provide more than enough light for paphs - in fact you want to be careful not to be too close as they could provide too much potentially.

Ross · #4 (**permalink**) 10-12-2008, 02:48 PM

I sort of agree with the above except, "need" and "desire" or "thrive" are different things. My Phals for instance are in full sunlight (when the sun shines). My Paphs and Masdies, the same. I supplement full sun with CF t5 bulbs (high output). I got the plants acclimated over a period of time so they wouldn't burn.

As stated above, you can't rate a t5 (or any other bulb) in foot candles. Foot candles are a relationship between Lux (or lumens) over a measured area and at a measured distance. I highly recommend purchasing a meter capable of measuring both Lux and Foot-Candles. It will be useful in monitoring light fall-off over time of your tubes as they burn in and age. The number of tubes you select is more a matter of area you want to cover, than it is light output. Certainly an 8 tube 48" fixture is capable of putting out more overall lumens than a 4 tube 48" fixture. But at 12"-20" there is a huge drop in light (light drops - falls off - at an inverse square of the distance). This simply means moving the light or plants further from each other has a dramatic affect in a short distance. Not that bad when figuring the sun. At 93 million miles (give or take a few) moving a plant a few feet has essentially no effect. But with any light source in your home, a foot or two could half or double the light, depending on direction. Sorry for the long-winded explaination!

ladyslipper · #5 (**permalink**) 10-12-2008, 02:53 PM

Hi guys, thanks for the info. Unfortunately my eyes tend to "glaze" over when this technical stuff demands some of my attention even though I know its critical. My real concern is my Phrags. This morning on one side of my grow stand the measurement (if I read it right) was on the hi side of 1500 FC. On the other side away from the window it was about 500 FC. I have rearranged my plants so that the Phrags are nearer the window. My stand is about a foot away from a north/northeast window. In the summer I have to shield the stand until noon as the sun is so intense but in the winter things aren't as nice. That is why I was getting concerned now I have finally found Phrags I have a good shot at growing, I wanted to see the little beauties bloom (like mad!!!!)

regards m

Ross · #6 (**permalink**) 10-12-2008, 03:00 PM

Quote:

Originally Posted by ladyslipper

Hi guys, thanks for the info. Unfortunately my eyes tend to "glaze" over when this technical stuff demands some of my attention even though I know its critical. My real concern is my Phrags. This morning on one side of my grow stand the measurement (if I read it right) was on the hi side of 1500 FC. On the other side away from the window it was about 500 FC. I have rearranged my plants so that the Phrags are nearer the window. My stand is about a foot away from a north/northeast window. In the summer I have to shield the stand until noon as the sun is so intense but in the winter things aren't as nice. That is why I was getting concerned now I have finally found Phrags I have a good shot at growing, I wanted to see the little beauties bloom (like mad!!!!)

regards m

I don't find this strange at all. If you measure 1500 FCs next to window, that's likely. I measure anywhere from 2000 to 3000 in the sun on my Paphs and Masdies. That's pretty high by most standards, but they thrive and no signs of burning. My quick assessment is get a two tube 48" fixture (make sure it's high output - HO) and hang that at the side of the stand away from the window. I'm sure you've seen this picture of my south-facing grow area with supplemental lighting:

I've since added another light to the right (a 24" 2-tube T5 unit designed for reef aquariums). It's pretty bright in there, but everyone's happy.