How to Choose an True Wattage LED Grow Lights 2021 Update

What are the benefits of LED grow lights?

Boosted growth, density, and resin production; tighter internodal spacing
Long bulb life; 50,000-100,000 hours (5 to 10+ years of consecutive use)
Energy efficient (30-50% more efficient than traditional lighting)
Lower heat-load / Reduced HVAC costs
No ballasts or reflectors, additional cooling equipment, or bulbs to replace
Spectrum, dimming, timing control (some fixtures)
Low profile (ideal for tiered racking systems)
Easy 'Plug-and-Play' setup
Safe to operate; No mercury

Wattage & Power Draw 

LED Grow Light specifications include the Wattage, or Power of the light. However, there is a great deal of confusion over Wattage and actual Power Draw. Why are there even 2 different specs and how does the customer decipher what is really going on? For example, MARS HYDRO TS 1000W is 1000 Watt grow lights but the actual power draw as stated on the product spec page is 150 Watts. Why??

First let’s remember that Power (Watts) = Voltage x I(Current)

LED plant lights are grouped by the current (Amps) of the diodes within the light. 1 watt diodes generally run at around 0.35 Amps, 2 watt diodes run around 0.5 Amps and 3 watt diodes run around 0.7 Amps. Diodes are not maximized with current so that the manufacturer can increase the lifespan, reduce the heat output, and supply a better grow light. In addition, different color diodes have different wavelengths and require a different supply voltage for the specific wavelength. The red and orange wavelengths require around 1.8-2.7 Volts and the blue and violet wavelengths require 2.7-3.5 Volts. Hence, following our W = V x I equation, a 3 watt red diode may only have a power draw of 1.5-2.0 watts and a blue diode may only have a power draw of 1.8-2.5 watts. That is why we have the stated wattage of the light and the actual power draw. Hence, the 1000 Watt grow light has 342x3 watt diodes, but the actual power draw is 150 Watts. Some LED companies do not publish the actual power draw. Be careful of these companies and make sure you make an apple to apple comparison when it looking for the right LED for your given grow space.

How many watts of LED power do I need compared to HID lighting?

Generally, 30-50% less wattage is needed depending on the efficiency of the LED grow light. More efficient grow lights exude more light while using less watts. Remember, that this is actual LED wattage, also known as wall wattage, not the advertised LED wattage that might be found in the title of the LED grow light. For example, an amazon advertised '1200W' LED grow light might only draw 500W at the wall

How Much Power You Need

To grow marijuana, you want between 30 and 40 watts per square foot of grow space. Of course, more wattage will give you larger yields (within reason) and less wattage will result in smaller yields.

NOTE: We are using the actual power here (and also in our table below), not the rated power. LED diodes are never run at full power, as this would considerably shorten their life. A 3-watt chip for example, will only run at approximately 60% of full power.

So if a fixture has two hundred 3-watt diodes, it is technically capable of producing 600 watts of power, but it will actually only draw about 300 to 400. Most manufacturers will list the rated power (600 watts), but this is obviously a bit misleading.

So, continuing the example from above, you need between 480W led grow light (16 sq ft x 30 watts) and 640W led grow light (16 sq ft x 40 watts) of actual LED power.

Your best bet in this case is to go with a light that draws at around 600 watts of actual power for this grow area. In terms of listed wattage, that equates to around 1000 watts.

The table below shows the wattage needed for common grow area sizes. Naturally, most grow areas are far larger. Use the values below to calculate your requirement.

For example, a 1000 square foot space would need 30,000 to 40,000 watts in total.

You get this value by first calculating how many 100 sq ft areas are contained in one 1000 square foot area (1000 divided by 100 = 10).

A 1000 square foot area contains ten 100 square foot areas. This means it would need ten times the wattage.

From the table, a 100 square foot area needs 3000 to 4000 watts. Thus, a 1000 square foot area needs 10 times that, or 30,000 to 40,000 total watts.

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