1or2 tubes t5 high output for catt

[weederwoman]

help please

I need some supplemental winter lighting for my greenhouse here in the dark and short days of rainy Oregon. My orchid area has only 1,000 foot candles of light in the middle of a normal dark day. I bought two four foot t5 high output one bulb fixtures (5,000 lumens). I have been spending hours searching the internet trying to find an answer to what seems to me should be an easy question: is one enough-are two too much. Tops of plants could be placed two feet from bulb for pots, one foot for mounted. I imagine many people would like to know the same thing. I know lumens and foot candles are totally different, so I hope to just use someone's experience, rather than try to work it out scientifically. I don't trust my light meter with this mix of sunlight + t5.
Thank you

[Ray]

For catts, I'd guess that being two feet from the bulbs is entirely too far for a single-bulb fixture used as a sole source of light, but as a supplement, it might have some value, but we cannot say exactly how much. I doubt 2 of them would be enough, as well. Light intensity fall-off is quite rapid.

For example, using a single, 2' T5 bulb, I measured 2000 fc about a half-inch from the bulb, but only 300 about a foot away - and that was with a good reflector. Without it, the light level was only about 100 fc a foot away.

Why don't you trust your light meter, as it's likely the best way of estimating you have?

By the way, a foot candle is a lumen per square foot.

[Ray]

I did want to add that PAR (photosynthetically active radiation) is a volumetric thing - rate x time. Even if the intensity (rate) is low, leaving the lights on longer will help (up to a point).

[weederwoman]

Ray

My light meter has two separate settings for daylight/high intensity and for fluorescent. The fluorescent only goes up to 1000 foot candles. It reads over the top on fluorescent when I put it under my lights at plant height. I can get my plants closer, the 1,2 foot figures I gave was as far away as I can get them. I will try to call meter manufacturer today to find out more about the product and mixed light usage. It was not a high end meter.

Thank you

[weederwoman]

I found a 2007 orchid board forum discussion on environmental concept light meters and t5 bulbs. Seems there are others with issues in the past. Any new input out there? Both t5 bulbs and E C meters are commonly used products, I believe.

Thanks