sun "wattage"

[DerbyCityNeps]

i dont know where this would go so i put it here.... does anyone know what "wattage" sunlight equals?? i know there is no wattage on sun... but hopefully you get what im asking.
Alex

 

[Not a Number]

Well Wattage actually is a measurement of electrical power (voltage x current) but most people associate it with light output when concerned with light bulbs. My blow dryer is rated at 1875 Watts but produces very little visible light (plenty of IR though).

But a Google search of "Power output of sun" linked to this page which gives a value of approximately 4 x 10e26 Watts (10 to the 26th power). That's ~400,000,000,000,000,000,000,000,000 Watts.

What you are really concerned with is Luminance or Illuminance (see this sticky thread), usually expressed in lumens.

 

[DerbyCityNeps]

woah... thanks! ive been wondering how strong the sun really was
Alex

 

[xvart]

Quote[/b] (glider14 @ Dec. 22 2006,10:48)]woah...

Woah is right. He's a beast I tell you, a beast!

xvart.

 

[seedjar]

Lumens is a good estimate of light output, but for the purpose of growing plants, what you're really interested in is a value called PAR, photosynthetically available (active?) radiation. Lumens measure light that people see - PAR measures the light that plants use for energy. Unfortunately, many bulbs are not rated in terms of PAR, so often lumens are your best guide to brightness. Because the spectrum we see in is different than the spectrum that plants photosynthesize, you need to pay attention to the color of light emitted by your bulbs, to make sure that your plants are getting light that they can actually use. This is measured by the color temperature of the bulb, which is usually a number in the thousands measured in degrees Kelvin, like 6500°K. I'm not sure exactly where the Kelvin scale comes from; it's some physics thing - I think it has to do with the color of light emitted by some sort of metal when you heat it to a given temperature or something. It doesn't really matter for our purposes - all you need to know is that you can use the color temperature rating to help match your bulbs to the colors of light that plants use, and try to match the intensity of the sun in those colors.
~Joe

 

[xvart]

Quote[/b] (seedjar @ Dec. 22 2006,4:03)]I'm not sure exactly where the Kelvin scale comes from; it's some physics thing - I think it has to do with the color of light emitted by some sort of metal when you heat it to a given temperature or something.

The Kelvin scale was created as the absolute scale of temperature meaning that 0 (zero) K is the absolute lowest theoretical temperature at which point there is no heat energy in matter. Essentially, all matter and atoms stop moving and radiating any heat. The increments of measurement for the Kelvin scale and the Celcius scale are equivilent; the only difference is the zero mark on each scale. Kelvin equals -273 deg. C (it's actually like 273.xx something) so zero degrees kelvin equals -273 deg C.

Of course this is the calculated 'absolute zero' and has never been achieved nor observed. Additionally, there is no 'degree sign' when shorthanding the temperature in writing like the little circle next to the F and C in other scales. A simple 'K.'

I knew majoring in physics in college would have some practical application!

xvart.

edit: it's 273.15 (I just looked it up). Interestingly enough, you only capitalize kelvin when it starts a sentence or you are referring to the Kelvin scale. You learn something new everyday! Needless to say I corrected those mistakes as well.

 

[Clint]

Ok... I thought kelvin temperature was a theoretical black body and the light it emits at different temperatures in the kelvin scale?

 

[seedjar]

I'm talking about the Kelvin scale of light frequency, which has to do with the temperature (relative to absolute zero, hence the necessity for measurements in kelvin) of a black body radiating light of a given color. Not the general measurement of temperature.
~Joe

PS - Excellent ninja skillz, Clint.

 

[Clint]

Ohhh.. OK lol. I believe you. Lol.

 

[xvart]

Quote[/b] (seedjar @ Dec. 22 2006,4:46)]Not the general measurement of temperature.

Well I guess it's back to school for me... Thanks for the follow up, Joe.

xvart.

 

[JB_OrchidGuy]

If you were to measure the sun it puts out about 8k to 10K foot candles on a summer day. I have no clue what that is in lumens, but I can get a reading for you tomorrow for the winter here in GA in lux or foot candles.

Joe has it correct though. Plants use a certain light to grow. They mainly use reds and blues. Reds I think induce flowering and blues induce foliage growth. IIRC You could have a very bright light, but if it is not producing the correct wave lengths for the plants it is un-usable to the plant. Although that can be over come by making the exposure of the light longer because alot of lights do give off most of the wave lengths. Some just put off more than others in certain wave lengths.