lighting Why Everyone Should Own Atleast 600W of Grow Lighting(Price Points)

TheLonelyHab

TheLonelyHab

So I wanted to do an economical assessment of whether a grow light system of 600w makes sense. To do this I will compare the price of this system (in Watts) to owning 3 1/4'' double pane windows.
 
The grow light system ideally will burn 600w of power and also emit 65% of that power consumption back into the room as heat. Thus you will need to run 600w of lights and cool 390 watts with your AC unit. Which totals to 990 watts of power.
 
Grow Light Consumption: 990 Watts
 
Now I own three windows in my one bedroom apartment. The area in square meters is (3.16, 3.52, and 2.08 m^2) (70""x70"", 70"x79", 46"x70"). These windows are 1/4" double pane, standard apartment windows. We can calculate the AC load in watts by thermal diffusion through ONLY the 3 windows (there will be more losses through the walls and ceiling!).
 
Thermal Diffusion can be calculated via the following formula...
 
Q (Watts) = (Thigh - Tlow)/Req​
 ​
Where Req is the equivalent thermal resistance of the window. It is calculated via the following formula... (this assumes two glass layers are surrounding one air layer).
Req = 2*Lglass/(kglass * Awindow) + Lair/(kair * Awindow)​
 ​
Typical apartment windows use 2.2mm thick glass layers surrounding 1.8mm of air which should equal 1/4 inch thick windows (2.2x2 + 1.8) mm = 6.2 mm or 1/4".
 
Req values for my three windows are (0.02494, 0.02238, 0.03795) degC/W.
 
On a summer day if it is 95 degF outside and my AC cools my house to 78 degF I will consume the following watts by cooling my apartment.
 
Wattage = (35 - 25.55) { 1/0.02492 + 1/0.02238 + 1/0.03795 } = (35-25.55) * 111.16 = 1049.5 Watts (I am using Excel to avoid rounding error)
 
Window System Wattage: 1050 Watts
 
If it is 95degF outside for 8 hours (I LIVE IN TEXAS WHERE IT CAN GET TO 105 DEGF!) I will consume 8.4 kWh per day which comes out to be 8.4 kWh * 0.12 $ / kWh = $1.008 per day or $30.22 per month
 
Having windows is more expensive than a 600W HPS :P. TIME TO PARTY!
 
P.S if you run your HPS in the winter that extra heat is going to heat your apartment so it only costs 600W to run.
 
Everyone on the forum GO BUY A HPS LIGHT! :P
 
:onfire:
 
kglass= 0.96 W/m/degC
kair    =0.024 W/m/degC
 
now imagine you are using a led light that requires much lower load on the heat. Also it needs to output less light to provide same amount of  growth in plant, so you can decrease the initial wattage. 
 
of course there are other benefits to a window besides just light that makes it "worth" more.
 
     I thought 
 
TheLonelyHab said:
 
 
The grow light system ideally will burn 600w of power and also emit 65% of that power consumption back into the room as heat. 
Click to expand...
 
     I'm pretty sure almost 100% of the 600 watts will end up heating your home. Even visible light and UV will end up being absorbed by the surfaces it shines on, and will eventually be converted into IR radiation. The only light energy that won't be converted to IR is that which is harnessed by photosynthetic pigments and stored chemically via covalent bonds in sugar. 
 
+1, the amount of heat ultimately produced by an 400W LED light, HID light, incandescent light, or 400W heater for that matter, will all be the same. The energy stored chemically is practically negligible.

dash 2 said:
I thought 
 
 
     I'm pretty sure almost 100% of the 600 watts will end up heating your home. Even visible light and UV will end up being absorbed by the surfaces it shines on, and will eventually be converted into IR radiation. The only light energy that won't be converted to IR is that which is harnessed by photosynthetic pigments and stored chemically via covalent bonds in sugar.
Click to expand...
 
Well to be fair, yes the light will be absorbed somewhere in the tent. However I didn't want to assume anything with regards to the amount of radiation through the window. The above comparison is a thermal comparison and not a radiation comparison. 
 
If the Window is sunless than there will be minimal watts added to the 1050 calculated. However if it is a Sunny Window then you need to add 1200 Watts/m^2 of window that is full of light. So assuming 50% of my windows are receiving full sun...
 
Additional Sunlight Watts = 1200 * (3.16 + 3.52 + 2.08) * 0.5 = 5256 Watts.
 
As you can see this is much more than the 210 Watts of light...
 
HPS Light Watts = 0.35 * 600 = 210 Watts
 
In fact if the window only receives one hour of sun than the HPS is still cheaper! The HPS is lower wattage but it is constant over the grow cycle!
 
So you can see the Sunny Window is much more expensive than the HPS. Although you could argue that you are getting more sun, comparing things on a thermal perspective is more practical because chances are you won't be receiving full sun in a window for 8 hours. We would have to integrate the solar spectrum based on the window's lattitude and longitude and calculate the clear sky irradiance as a function of time.
 
We can do this if you guys wants too!  :dance: 
 
What do you guys think?
 
Full sun outdoors and AC on?

Put the plants outside: you'll lower your electricity consumption, keep your apartment cooler, and give the plants more light :)
 
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