# Maximum Light requirements for plant?



## super g (Nov 27, 2010)

Hello all, 

Well the title says it all. Do pants have a maximum amountnt of light that they can use? especially during flowering?


Was reading a book and came across a table that sujested that there was a maximum light requirement for plants - if you went above it you would not yeald any extra "fruitage" from a plant 

What do you guys think abt this, from your experience?

Doesn't seem right to me: from seedling to veg to flower - when plants grow bigger then they require more light, Doesn't that suggest if u grew a plant bigger they could handle more light- and so - they would could grow larger/more buds if more light were available ?

Here's the table


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## Briester Behemoth (Nov 27, 2010)

Just saw this in Cervantes book. IMO based on the description the title should read Minimum Light requirements for Plants

Maybe its based on the fact that the sun emits 10,000 foot-candles on a bluebird day?

On a side note, if you are reading Cervantes book, some of the info in it is just plain wrong so this table might be too. Is there even an artificial light that can produce 10,000 foot-candles?

Anyone who can answer this question can you answer this: How do I measure foot-candles? I know how to measure lumens but I never heard of an instrument that can measure foot-candles.


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## super g (Nov 27, 2010)

yea thanks for the reply 
i know what u are saying abt this book its filled with bad info 
i think ur right abt the minimum maximum thing lol makes sence now !


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## SCARHOLE (Nov 27, 2010)

http://www.thctalk.com/gallery/data/500/HPS-Light-Distance-Chart.jpg


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## TaoWolf (Nov 27, 2010)

Briester Behemoth said:


> On a side note, if you are reading Cervantes book, some of the info in it is just plain wrong...


Agree about some of the info just being plain wrong. But I've seen 500fc/5,000lux thrown around a lot, so the info in the chart is probably ballpark correct at the seedling and clone stage. After that I think it's more of an issue of ensuring the bottom growth is continuing to get that ~500fc/5Klux through the canopy - and that would vary a lot according to plant height, foliage, and growspace... 



Briester Behemoth said:


> Is there even an artificial light that can produce 10,000 foot-candles?


It's more just a matter of proximity to the light:

View attachment 1291222



Briester Behemoth said:


> Anyone who can answer this question can you answer this: How do I measure foot-candles? I know how to measure lumens but I never heard of an instrument that can measure foot-candles.


1 foot candle is equal to 1 lumen over an area of 1 square foot.


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## ooli (Nov 27, 2010)

super g said:


> Hello all,
> 
> Well the title says it all. Do pants have a maximum amountnt of light that they can use? especially during flowering?
> 
> ...


Well, there's two things you have to consider:
You can't produce more, in any aspect, than the genetics will really allow, and
Too much light can hurt the plant; i.e. light bleaching.



> Doesn't seem right to me: from seedling to veg to flower - when plants grow bigger then they require more light, Doesn't that suggest if u grew a plant bigger they could handle more light- and so - they would could grow larger/more buds if more light were available ?
> 
> Here's the table


Yes, you can spread light across a broad area, like foliage, and in that sense; the bigger the plant, the more light it can handle, but one isolated area can only take so much light.

~ooli~


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## mindphuk (Nov 27, 2010)

You have to look at many factors. There are both light-dependent and light-independent reactions taking place. Then you have to look at the limiting factors that allow these processes to proceed. It would seem to me that light-dependent reactions are limited first by available light but then when you reach a certain point, they are limited by co2. If co2 is supplemented, then the rate of the light-dependent reactions will increase as long as everything else is optimum including temperature and the amount of chlorophyll in the leaves.


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## Uncle Ben (Nov 28, 2010)

Briester Behemoth said:


> Just saw this in Cervantes book. IMO based on the description the title should read Minimum Light requirements for Plants
> 
> Maybe its based on the fact that the sun emits 10,000 foot-candles on a bluebird day?
> 
> On a side note, if you are reading Cervantes book, some of the info in it is just plain wrong so this table might be too. Is there even an artificial light that can produce 10,000 foot-candles?


That book contains some of the best info on lighting to found.

The issue is understanding and finding out a plant's light saturation point. Charts are worthless as they don't take into account all factors that contribute to what a plant actually receives.

HID's can be more powerful than than the sun, even the smaller ones. Here's a test I did years ago using small horizontal hoods with spectral, gullwing insert:

*>>DISTANCE FROM LIGHT..................F.C. READING*
*.......................250W HPS...............600W HPS*

*Within 6" (Way off 10K f.c. scale, for both lamps)*
*6".......................10,000...............10,000+ f.c.*
*8".......................7,100................10,000+*
*12"......................4,800................8,700*
*18"......................2,800................5,600*
*24"......................2,000................4,200*
*30"......................1,400................3,300*

*Frame of reference: sun = 9,000 - 10,000 average, clear day;*

*Cool White fluor measured 2" from bulb = 1,200*

Enjoy,
Uncle Ben
>>

Looks like there is a HTML tech problem on spacing of the zeros FWIW.

Use a F.C. light meter that registers to 10K f.c.

UB


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