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.
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.