# Photo period Vs wattage



## potatoes (Jun 25, 2010)

Hi,
My biology teacher told me today that if you have a 20watt bulb for 16hrs, it is the same as a 40watt bulb for 8 hrs. I am skeptical, but if it is true it could help a lot of people make due with there improper lighting. If possible, can you explain why he is wrong/right?
Thanks


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## Newt (Apr 1, 2004)

Watts is INPUT to a bulb not output of a bulb.


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## THE_MOTHER_JEWELS (Feb 10, 2011)

There is some truth there. Say , we wanted to heat a cup of water for example.

That does not address Circadian Rhythms
http://www.sciencedaily.com/articles/c/circadian_rhythm.htm

I need 8 hours of sleep a day - can not stay up all week and sleep for 56 hours on Sunday , , ,
I need to breathe - can not inhale for 12 hours, followed by 12 hours of exhaling, , ,
I need food- can not eat this month - poop all next month.


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## potatoes (Jun 25, 2010)

Thanks for the responses. So it dosnt work like in extreme cases, but i am under the impression that it works within more moderate variation, like if you need a 40watt bulb, you could use a 30 watt bulb for a bit longer, but not a 10watt bulb for 4X as long. is that correct? 
I understand that wattage is input, but it seems how a lot of people measure thier lights. is there a better way? lumens?


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## joshvito (Apr 6, 2009)

You should measure your light in PAR output.
There is a lot of factors that affect light available to plants.
If you want to read more, here

an also interesting related read.
http://www.barrreport.com/showthread.php/6972-The-light-limiting-growth-management-method

If the purpose of your question was just for discussion, its an interesting theory. Maybe you should set up an experiment in your biology lab?


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## potatoes (Jun 25, 2010)

Awesome! I love learning more about this hobby. :jaw: I just saw how much light I have, I really need to raise it! I diddnt know T5HO was that intense


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## Newt (Apr 1, 2004)

Lumens are based on the human eye sensitivity to light which peaks in the green region of the spectrum. It is based less on the red/blue spectrums that plants most efficiently convert for photosynthesis.
PUR would be better than PAR


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## joshvito (Apr 6, 2009)

Where can one get a PUR meter?


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## klink67 (Feb 11, 2011)

I run 18/6 cycle with a strong t-5 lights and get excellent growth.


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## Newt (Apr 1, 2004)

joshvito said:


> Where can one get a PUR meter?


You probably wont find a commercially available P*U*R meter; or at least an affordable one. The *U*sable radiation is typically calculated from the *A*vailable radiation.

Hoppy has a nice thread going but it assumes all bulbs of a particular size are equal > If I am reading it correctly (for instance): he took a T12, did some P*A*R measurements and drew a curve. That is accurate for THAT particular bulb. Bulbs output different energy spikes (microeinsteins) in different areas of the spectrum. This affects P*A*R and P*U*R. I have some T8 Aquarelles and ADV850s by Philips that blow away, sometimes by double, other T8s and even CFs of twice the wattage.


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## Dave-H (Oct 5, 2010)

I just bought an Apogee PAR meter direct from the manufacturer for about $350.


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## potatoes (Jun 25, 2010)

lights are confusing :boom:


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