How Much Light is Enough?

[GiftOfChilies]

I've seen many questions about how much light is enough, and I thought I would add some additional facts to the discussion.

How much light is enough?

Let's first consider the Sun.
The Sun is considered a black-body emitter with a temperature of 5778°K.
On a perfectly sunny day as sea level on the equator the sun has an irradiance of about 1000 W/m[sup]2[/sup].
According to the PV Solar Radiation Chart determined by NREL, the southern states receive an insolation of about 5kWh/m[sup]2[/sup]/day.

Photosynthesis occurs in two frequency bands, a red band and a blue band.
The red band for photosynthesis is approximately from 690nm to 630nm.
The blue band for photosynthesis is approximately from 500nm to 400nm.

A black-body emitter at 5778°K will emit 6.67% of its power in the 690nm to 630nm band and 12.57% of its power in the 500nm to 400nm band.

So to match the 5 kWh/m[sup]2[/sup]/day insolation of the southern states with a 16 hour light cycle you would need 20 W/m[sup]2[/sup] of red spectrum in the band from 690nm to 630nm, and 39 W/m[sup]2[/sup] of blue spectrum in the band from 500nm to 400nm.

To size the light you need to apply an efficiency factor depending on the light source. A decent high power red LED will be about 38% efficient and a high power blue LED will be about 50%. A T8 florescent light is about 30% efficient but not all of the emission will be within the red and blue bands so that efficiency will be decreased depending on how much wasted spectrum is present.


I hope this information will be useful for your future lighting decisions.

 

[Capsicum]

"To size the light you need to apply an efficiency factor depending on the light source. A decent high power red LED will be about 38% efficient and a high power blue LED will be about 50%. A T8 florescent light is about 30% efficient but not all of the emission will be within the red and blue bands so that efficiency will be decreased depending on how much wasted spectrum is present"


How about HID lighting like hps or metal halide? They have to be close to 100%.

 

[willard3]

50 watts of a lousy source, ie, 70 lumens/watt source per square foot of plant canopy
30 watts of good source, ie, 100 lumens/watt source per square foot of plant canopy

You are trying to get to or slightly above 3000 lumens/square foot of plant canopy.

 

[GiftOfChilies]

How about HID lighting like hps or metal halide? They have to be close to 100%.

Lets first consider spectral effeciency of Metal Halide:

Metal Halide Spectrum: All spectrum from 630nm to 500nm is wasted
It is about 24% effecient at making it's light.

And HPS:

Again all spectrum from 630nm to 500nm is wasted.
HPS and MH are both gas discharge lamps and be mid-20% eff. for watts at the wall to watts light.

 

[Capsicum]

So what is good then?

I harvest more per square fot inside then outside becasue there is no cloudy day inside just light that is on all day. According to your chart HID are only 20%, I have hard time believing that even though it is science lol.


And BTW can you show a blue spectrum HPS, not these cheap bulbs.


"HPS and MH are both gas discharge lamps and be mid-20% eff. for watts at the wall to watts light. "

I do not agree at all. So HID is less effective then T8, what?!?!?!?!?!?!?! That is very very wrong. At lighting, NOT GROWING.


Inside UNDER HID =75f/perfect watering/perfect temp/no cloudy days. Plants grow quiker and more healthy.
Outside=stress of temps/rain/weather/ect/100% effective lighting Indoor still beats harvest per square foot.


One more thing. Temp. has a huge roll in photosynthisis, peek photosynthesis takes place at75-80 degrees F. That is why hps only needs to be 30% as the sun. Because plants are growing quiker with fake HPS light at 70 degrees in a cooled grow room, and they grow very very slow outside at 90+.

Why did my text get like this?!?!?!?

 

[Nagel]

Ok, so thats one type of MH and one type of HPS.. There are many choices, with different color spectrums out there..I have a hard time believing that those two charts cover all possibilities of MH and HPS lamps..

MH range from easily under a 4700k lamp to well over a 14,000k lamp. Their spectrum varies just as much..

And what about PAR??? Photosynthetically Available Radiation?? PAR is the important one.. Lumens is garbage! You can get a high rating of lumens on a Halogen bulb, but its got diddly for PAR, hence why we don't use Halogens in growing photosynthetic organisms..

 

[Capsicum]

Thanks Nagel you agree too then. Lets see a Hortilux blue spectrum HPS!!!!!!!


With all that said, nothing beats the sun.

 

[Nagel]

Capsicum - agree on both points.. HID lamps have been researched high and low on two hobbies.. Coral Growers and Weed Growers.. Both groups with substantial investment into their systems to get the most possible growth in the shortest time for the lowest cost while maintaining high quality (I know about the coral side from personal experience, and well, when you research growing anything, you can't help but stumble on some weed forums).

LED is new and exciting, great for low heat situations, but they are not at their full potential yet.. and are a hell of a startup cost.

HID has a TON of options, and is the closest we can get to the sun (even though they still aren't diddly compared to the sun). I've got everything from 70w MH to 400w MH and HPS here, and done NO, HO and VHO tubes (still like my VHO for seedlings, dunno why everybody uses the crappy shoplights), had CFL lighting as well as Power Compacts.. Even have some Mercury vapor lamps from when I didn't know any better. When it comes down to it, MH is my first choice.. I do like my VHO systems for seedling racks, but for growth, a 400w MH is my staple..

 

[Capsicum]

"HID has a TON of options, and is the closest we can get to the sun (even though they still aren't diddly compared to the sun). I've got everything from 70w MH to 400w MH and HPS here, and done NO, HO and VHO tubes (still like my VHO for seedlings, dunno why everybody uses the crappy shoplights), had CFL lighting as well as Power Compacts.. Even have some Mercury vapor lamps from when I didn't know any better. When it comes down to it, MH is my first choice.. I do like my VHO systems for seedling racks, but for growth, a 400w MH is my staple.. "



Yup, after trying even t5 high output, MH wins. Yea its fun trying those mini HID systems too. I got a 150 hps, came with the hood and glass lens and the bulb!!!!! That next to my little MH would make a great lighting for peppers and tomatoes. I used to grow indoor cherry tomatoes. At first I thought I could use hps but they got too tall, I then use a blue spectrum hps bulb which also increased the lumens and got some blue. I found I could grow them all the way for a long time with just the blue spectrum hps. They where indeterminate bush type, almost dwarf like and did not get out of control. The interesting thing is how they just keep growing tomatoes and going and going as a determant would not do that. I wish I knew about peppers when I grew inside!!!!!!!!!!!!!! From my experience I should of just got a 400w MH not hps.

I like to grow outdoor now only and take advantage of the sun, 100% effectiveness

 

[Nagel]

Here ya go..

http://www.manhattanreefs.com/lighting

Thats the saltwater reef community's lighting god.. If there is a comparison between lights, you'll probably find it there..

(yes, I know its about reef tanks, but the lighting requirements are as demanding, if not more)