Maximum footcandles? - Orchid Board

Royal · #1 10-27-2008, 10:27 AM

Cold temps are here, and the OB has really helped my collection explode! So instead of windowsills this winter, I set up a borrowed HID light. It's a 400w HPS and really puts out some light. I think the neighbors are starting to wonder.

My question is how much is too much light? I grow mostly high light Cat alliance orchids, but my new (cheap) light meter is reading 4,500 - 6,000 fc's depending on plant height. Is this going to cause me problems? Thanks in advance,

Magnus A · #2 10-27-2008, 11:09 AM

Hello

Can you keep the plant leaf cool and not warmer than your body temp you should be fine from heating dammage. About the light intensity you have to look at the leaf color. If healthy light green you are OK if they turn yellowish you have problems but you may not get burnt leafs....

Short:
Heat gives cooked leafs, burn mark!
High light, (low to moderate temp) gives sickly looking leafs, not good.
combination of both leads to disaster....

Royal · #3 10-27-2008, 02:50 PM

Thanks Magnus,

I like to push plants to their upper light tolerances so I do pay close attention to leaf color. That's a great piece of advice and made a huge difference in my growing early on. Good insight on the leaf temperature too. I just had to make the switch from outdoors to under lights kind of suddenly and I wondered what other veteran light people thought of these intensities.

Ross · #4 10-27-2008, 04:12 PM

I resisted responding because I have no current experience with HID. But if your meter is accurate, That is way high for most indoor lighting. I try for 1800-2000 FCs for my Orchidarium and up to maybe 3500 FCs on a good day for my grow window (south-facing bay window). Those numbers are either wrong, or very high. As Magnus says, the plants will let you know. I'd say in less than a weak.

Royal · #5 10-27-2008, 04:56 PM

Thanks Ross, That's kind of what I was expecting to hear. The light meter I have is a cheap one, but it is giving me steady readings, and trails off smoothly as distance from the light is increased. This leads me to believe that it's pretty close.

The light is almost flush with the ceiling, so I'll have to rethink the bench set-up to increase the distance. Oh well, it wasn't that great of a setup to begin with.

Ross · #6 10-27-2008, 05:17 PM

Quote:

Originally Posted by RoyalOrchids

Thanks Ross, That's kind of what I was expecting to hear. The light meter I have is a cheap one, but it is giving me steady readings, and trails off smoothly as distance from the light is increased. This leads me to believe that it's pretty close.

The light is almost flush with the ceiling, so I'll have to rethink the bench set-up to increase the distance. Oh well, it wasn't that great of a setup to begin with.

Royal, before you do something drastic and expensive you could consider a self-zero-ing calibrated meter such as []Sper Scientific Light Meter Lux & Foot Candle | Technika Pricey, but probably would save you in the end if you plan to constantly deal with lights. The foot-candles only model only goes to 2000 foot candles, so would be a waste. Think about it: take a reading when bulb(s) are new and then every month after. Never replace bulb(s) until it (they) drop below your given checkpoint. That's how I measure mine: replace when I get a reading below 1800 FCs. I depend on mine and you would one day forget how much you paid for the thing. Just a strong recommendation.

Magnus A · #7 10-27-2008, 05:35 PM

For your plant that is used to high light outdoors I think the temperature will couse the biggest problem!

So buy a fan!

I found that the slightest air movement cooled down the leaf significantly! But with airmovement the transpiration get larger and the evaporation from the media in the pots increase, so keep an eye on the watering so you do not dehydrate your plants.

And I use my light meter as Ross. I just check the degradation of the light by time and do not bather so much for the actually reading. But I have calibrated it compared to a professional meter meassuring only the part of the spectra used in scientific litterature for growing green plants. It was surprisingly accurate under my T5´s

ericst11 · #8 10-27-2008, 10:39 PM

I have to agree with magnus about the heat that is a big problem with those lights. I run a 1000 watt HPS and its three and a half to four feet from my plants and the growth rate is amazing . But i run a fan on high pointed right on the light to distribute the hot air and one to move the air in the room . A good thing to remember is if you have a basement use it there because in the winter a basement is cool and the light heats your room and in the summer it stays cool so you don't cooking your plants. good luck

Royal · #9 10-28-2008, 09:22 AM

The whole setup is in a poorly insulated shed/building. Due to fall temps it doesn't get warm in there at all. I felt the leaves last night after posting this thread, they were actually kind of cold to the touch. When it warms up enough to cause excessive heating in the room, most will get moved back outside. I'm keeping a close watch for now. I'll let you all know what I decide.

ericst11 · #10 10-28-2008, 11:14 PM

If i were you I'd line the roof ,walls and floor with celitex foam board. some times you can find it with a silver backing that is good for reflecting the light and it will keep the shed warm.