How do you measure adequacy of artificial light?

Begonia2005(7)September 27, 2012

I continue to have some unclarities about fluroescent light. I have recently bought Walmart's grow light which many people have given very good reviews for growing AV-s under it.

I have installed it, as shown in my other thread about light, but at the eye-level I did not feel it provides sufficient light for the plant.

I read that in order to know how much light a plant is getting at any time, you need to place a light-meter at the plant level, right where the light falls...and the meter will tell you how much ftcandles it gets.

Well...where my plant sits under WallMart's grow tube, no further away than 6-7 inches below the plant...the light level barely reaches 200ftcandles!!

I read the light output must be at least 500ftcandle to mean anything for the plant.

In that case, how come that so many people seem to grow plants successfully under such an apparently weak tube?

I have one other CFL bulb in a decorative lamp; that one seems to spread more bright light...but even under that one, when I measure the actual light level reaching the plant, it is no more than 300-400 ftcandles, with the lamp at 7-8 inches above the plant.

I did measure the light level when the window gets naturally sunny...and then I get indeed 1000 ftcandles (the "real deal" the plant seems to need).

So how do people grow AV-s under artificial lights when they seem to provide inadequate amounts of light at the recommended distances? Or is it possible that this light-meter I am using is not that good?

Thank you for any clarifications!

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I don't know where your light meter came from. I know I got one at Lowe's that didn't work. At any rate, trust me on this, since I have the same grow light. Your setup looks perfect. I grow plants successfully that close/far from the light. If it needs more light over time it will show you by reaching leaves up and then you can place it on something that elevates it closer to the light and / or increase the amount of time the light is on. I have some plants that need to be closer than yours is, and some that need more space. I have found just a few that need more light than that grow light. Those I have near a window with some lining blocking the direct sun but still giving more than the grow light. In general though, your new light should be fine. You can start with around 8 hrs a day and increase gradually as needed. I think my healthiest plants are not at around 12-14 hrs, but I did not start them out at that. I disagree that leaves have to be very close to flourescent lights in order to burn. I've had way too much trouble with plants that weren't that close to flourescent lights that still got too much light. That's why I use the light that is like yours. It's not as bright/intense and leaves room to adjust plants and lighting time as needed.

I agree that whatever was wrong with your plants' rotting leaves doesn't look light related at all. Repotting probably fixed it. Sometimes something in the soil content, fertilizer, water amount, can irritate the plant or cause damage & rot. I'm guessing you caught it in time.

Good luck.


    Bookmark   September 28, 2012 at 12:23AM
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P.S. I forgot you planned to use your window light during the first part of the day. So you will not want to add 8 or 9 flourescent light hrs after that, at least not unless later on you discover the plant needs that much light. You will have to experiment but I think you can get it right.

    Bookmark   September 28, 2012 at 7:52PM
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So how do people grow AV-s under artificial lights when they seem to provide inadequate amounts of light at the recommended distances?

If inadequate means two reading lamps with energy efficient 13 watt florescent bulbs at four feet away from the AV table with east to southern exposure windows that also provides good cloudy sun light too. Then how I get AV's to flower nicely time after time wouldn't be agreed on in many ways by some others.
Although there are a few common problems with plants that wont grow productively they could agree with:

Top three reasons in order:
My suggestion is to solve problem one before moving on to problem two.

    Bookmark   September 28, 2012 at 9:21PM
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I have done everything I know about problem 1. The soil is as light and aerated as I know to make it. Some av potting mixture, perlite, vermiculite. It seems fine to me. I still think the lighting has been the biggest problem. Granted, it has been slightly les than a month since I have been using it and one plant is starting to show results. I still don't know what caused the other plant to lose its leaves ...but maybe I just need to wait longer.

    Bookmark   September 28, 2012 at 9:45PM
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Begonia ...

I'm not sure that I've mentioned this before, but there is a podcast about growing African Violets available to view at the link.

Annie has been doing a weekly podcast on African Violets since July of this year. If you check, I believe that it is in episode 2 that she talks about lighting.

Annie does a great job of explaining the mysteries of AV growing and showing, and she does so in a way that is inviting, entertaining, and informative.

Here is a link that might be useful: Annie's All About African Violets Podcast

    Bookmark   September 29, 2012 at 10:03AM
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I'm sorry, Begonia, ... Annie talks about lighting in episode 7 at the link.

Other episodes deal with soil, watering, fertilization, etc.

They're all very enjoyable and informative.

Here is a link that might be useful: August Episodes of Annie's All About African Violet

    Bookmark   September 29, 2012 at 10:16AM
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Asa far as the light meter is one called "Three Way", found it at Hope Depot and it also measures Ph and moisture. I am not sure how accurate it is, but when I put it under the Walmart tube, even very close/glued to the tube, it will not go above 200 ftcandles to save its life.
I went outside (on a relativelty cloudy day) and it went well above 500 ftcandles. Then I placed it under the CFL spiral bulb in my decorative lamp and it doesn't register much here either (maybe 300 or so). Then I placed it under a led light under my kitchen cabinet and it went close to 1000.
For whatever reason, this light meter will not register much at all under the Walmart grow light (the 10-11 dollar one) and not even the CFL bulb. Yet, I think the plants I've b een keeping under the CFL bulb are starting to show some signs of scorched maybe the meter doesn't register flurorescent light that well.

Yet I know many people praise the WM growlight and say they have gotten great results with it.

I will just have to go by experience.

    Bookmark   September 29, 2012 at 1:05PM
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nyxx(z7 Virginia)

The only experience I can go by about your light meter is I have found that anything that says it will measure more then one thing is never really any good at measuring anything.

I think you have everything set up right for in general. Now all you need is time to see how the plants react and bloom. You can't adjust everything until the plants tell you what it is you need to adjust, if anything at all. Patience is a virtue. =o)

    Bookmark   September 29, 2012 at 1:35PM
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I suspected that about the meter - "Jack of all trades" symptom...

Right now though, light is my last I have just discovered that at least some of my plants have probably had mites. I opened another thread about this...and I have no idea what to do with the remaining 3 plants, two of which have been recently bought. I don't know whether they had time to get infested too, whether I should spray them with something preventive..

I just never thought that I would have to deal with pests that soon, so I never studied up on this topic.

    Bookmark   September 29, 2012 at 2:19PM
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Why do you suspect mites, Begonia ... ?

    Bookmark   September 29, 2012 at 10:45PM
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I have opened another thread. I explained there.

    Bookmark   September 29, 2012 at 11:04PM
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One more experiential note about lighting ...

As you can se by your measurements, it's very hard to give your plants TOO MUCH light, given recommended distances from tubes, bulbs, etc. and reasonable timing (12 hours max.).

I also allow my plants to get full sunlight through my windows. I'll only shade them a bit in the heat of summer.

And I've rarely experienced ANY leaf-burn.

    Bookmark   September 30, 2012 at 7:51AM
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