Do T8s Provide Enough Light?
 

I have 2 noID phals and a paph delenatii and a paph magical venus under a Sylvania/Gro Lux 40 watt T8 fluorescent fixture. I took a light reading with my camera and the light measured only 500 footcandles! Maybe measuring it with a camera doesn't work so well. I also tried the "hand trick" and I saw absolutely no shadow whatsoever on my plants. The plants have been under the grow lights for around 6 months and a growing roots and leaves like crazy. My orchids are around 2-3 inches from the lights. I might get a light meter to test the light. What do you think of my setup? I bought one noID phal in full bloom in March and it shows no sign of growing a spike. It has grown 3 leaves over the past year and is currently growing around 8 or more new roots. I also should say that I have a small ceramic reptile heater that raises the temperature to around 85F in the day and temps drop to 60F or 65F at night. Any help, experience, and opinions would be greatly appreciated.

If you need more light intensity, move the plants closer to the light.

I have my orchids almost touching the light.

T8's should provide enough light for the plants you listed. I have a delenatii in bud right now under T8. I keep mine about 5-6 inchs from the bulb. It's been awhile since I took a reading, but I want to say it was somewhere near 800-900 FC. I try to dig out my meter tomorrow and take a reading for you.

Bill

How old are the bulbs? Tubes decrease in light intensity over time. might need to replace them.

I just got the bulbs this fall. How often should I replace them? I know you aren't supposed to let them burn out before you replace them.

I've heard people say replace them every year, but I don't think anybody actually does that. At least every couple of years. Yours shouldn't be bad so soon.

A picture might help...

I have heard one year replacement for T12 and T8 bulbs, and 2-years for T5, but we had a power surge (trees dragging down line in heavy wet snow) that blew out 5 T5 ballasts, and when I replaced the fixtures, I thought I'd be smart and save the new bulbs for replacements, and just use the old ones.

The "old" bulbs were about 1 year old, used 14 hours a day, and the intensity reduction was noticeable to the naked eye,

I'm sticking to one year from now on.

For the orchids that you are growing, the amount of light sounds fine. Other than moving the plants closer, you can also increase the amount of hours that the lights are on. You can go up to 16 hours of light a day, which is actually what many commercial growers do here (be they orchids or vegetable crops)

I've also heard the recommendation of changing the tubes once a year, but I tend to do it every 2 years. I don't have a light meter, but when I put the new tube in, the difference is more than noticable. I think mine are due for a change now, they seem dimmer than I remembered, and am having trouble blooming some things that are usually fine.

I've heard two things. 1) You should not use artificial light to prolong daylight hours for too much longer. 2) Leaving artificial lights on for longer does not make up for less intensity. Are these things true? They seem true to me but maybe they aren't.