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How to choose a grow light

At the equator the sun lands 950 watts per square meter per second (950 w/M/s).  That is roughly 100 watts per square foot.  Most plants in nature do not get that much.  We target 50W per square foot form massive growth!

What size light(s) do you need?

Light Size
Light Only
covers sq. ft.
Plus Sunlight
Covers Sq. Ft.
Cost for a 16 hour day @$0.08/KWH
100w -150w
3 ft.
4 ft.
$ .13
175w
3.5 ft.
6 ft.
$ .14
250w
5 ft.
16 ft.
$ .24
400w
8 ft.
25 ft.
$ .38
600w
12 ft.
49 ft.
$ .57
1000w
20 ft.
64 ft.
$ .96

Depending on your plant variety, plan for 40-75 watts per square foot.

What size electrical service or breaker do I need for plant grow lights?

Here are calculations so you may properly size your light for your circuit breaker. No one needs a fire!

The formula for converting Watts to Amps is : Watts = Amps * Volts

The formula for converting Amps to Watts is : Amps = Watts / Volts
 

SAFETY WARNING: Only use 80% of the circuit breaker capacity!

 

What is the Amperage of Plant Grow Lights?

Light Size
@110V
@240V
1000W
9.1Amps
4.6 Amps
750W
6.8 Amps
3.4 amps
600W
5.4 Amps
2.7 Amps
400W
3.6 Amps
1.8 Amps
250W
2.3 Amps
1.6 Amps
100W
.91 Amps
.5 Amps

110 volt maximum safe wattages:
10A * 110V = 1100W and 80% safe usage is 880W
15A * 110V = 1650W and 80% safe usage is 1320W
25A * 110V = 2750W and 80% safe usage is 2200W
30A * 110V = 3300W and 80% safe usage is 2640W

  240 volt maximum safe wattages:
10A * 240V = 2400W and 80% safe usage is 1920W
15A * 240V = 3600W and 80% safe usage is 2880W
25A * 240V = 6000W and 80% safe usage is 4800W
30A * 240V = 7200W and 80% safe usage is 5760W

Remember that a circuit services more than one power outlet.
 

Plant Grow Lighting Conversion Factors

1 lumens /sq. meter = 1 lux
1 lumens /sq. foot = 1 foot-candles
Lux =0.0929 * FC
1 F.C. = 10.76 LUX
1 Micro Einstein (umol) = 7.62 F.C.
1 WATT / MTR2 = Output Bulb divided by Square meters
1 MTR2 = 10.76 FT2
1 WATT = 408 LUX
1 WATT = 37.9 F.C.
 

What type of plant grow Lamp(s) do you need?

Plants see colors differently than people.  People's eyes are focused in mainly Yellow.  Plants mostly use the Blue's and Red's from the rainbow.  Some lamps are more full spectrum than others, all fall into one of three categories.  Vegetative (grow), Flowering (Bloom) and Full Spectrum (Start to Finish).  Veg bulbs are generally Metal Halide.  Most flowering bulbs are High Pressure Sodium.  Only a few bulbs live up to the claim of being full spectrum.  Fluorescent lamps also come in a grow (cool) or bloom (warm) spectrum.  Another way to rate the color of bulbs is Kelvin or K value.  Both HID and Flourescent; grow bulbs have a higher K value (4K to 10K) where bloom bulbs are lower K (2.7 K to 3K).

 

Plant:                                  

Recommended

Footcandles:

Azalea
1000
Chrysanthemums
2000
Coffee
1000+
Cucumbers
4000
Coleus
1000
Cineraria
1000
Gloxinia
1000
Saintpaulia
1000
Geranium
1500
Pepper (Sweet)
2000
Everbearing Strawberries
1500-2000
Sweet Pea
1500-2000
Tomatoes
1500-2000