How do I calculate how many watts an LED is?
The formula to calculate the max wattage on an LED is simply the maximum current (measured in Amps), multiplied by the forward voltage of the LED (at max amperage).
How do I calculate how many watts an LED is?
The formula to calculate the max wattage on an LED is simply the maximum current (measured in Amps), multiplied by the forward voltage of the LED (at max amperage). This wattage however is the theoretical maximum and in most cases is NOT what the LED is actually drawing from the wall. Make sure to multiply the drive current (ie. 1.4A) by the forward voltage (ie. 36V on most cobs) to see what the actual theoretical draw is (1.4A x 36V = 50.4 Watts). As always these are theoretical calculations and a kill-a-watt meter should be used to accurately measure wattage.
How do I know which drivers to use?
The first decision to make is whether you want a dimmable or a non-dimmable driver. Dimmable drivers have a few advantages:
- Soft ramping up/down of light to avoid shocking plants
- Can be programmed to turn on at only specific times of the day using a controller, without the use of a wall timer
- Ability to dim down light when plants are young or don't need full power
Once you know which type of driver you need, you’ll need to look at the current (mA) output of the driver. For non-dimmable drivers they will only output one current level. For example, the LPC-35-700 driver will output 700mA at all times, regardless of how many LEDs are attached to the driver (assuming you’re running one string in series off the driver, as opposed to say multiple parallel strings).
Dimmable drivers on the other hand have variable current levels. Please check the product description page and/or technical data sheets for the current range. Typically speaking we look at the maximum drive current and try to ensure that all the LEDs on your string are capable of handling this amount of current, even if you plan on dimming. This is a fail safe in case your dimmer fails, or is accidentally turned all the way up.
To figure out how many LEDs a driver can run you’ll need two pieces of information: the driver’s output voltage range and the forward voltage required by the LED at the given current level that you would like to run the LEDs at. As an example, the HLG-320H-C1400B driver has a voltage range of 114-229. The CREE CXB3590 COB LED requires ~35V at 1400mA. Thus, the minimum number of these LEDs required is 114V divided by 35V. 114/35 = 3.26, so we round up and the minimum number of LEDs is 4. For maximum LEDs, we divide 229V by 35V and get 6.54. We round down and get 6 LEDs. Keep in mind the voltage required by each LED can be quite different so you may need to do these calculations for each of your strings.
What mA driver should I use for my COBs (assuming all 36V COBs)?
1050mA- Use this current if reducing heat and electricity consumption is your first priority. COBs will be cooler and more efficient but you’ll need more of them so it will cost a little more. This is usually not recommended if you have a thick canopy to penetrate unless you're also using a secondary reflector/lens.
1400mA- This is becoming the industry standard as it's a great balance of initial cost, heat, efficiency, and canopy penetration.
1750mA- For a slight reduction in initial cost, and a slight increase in canopy penetration. Will be slightly warmer and less efficient than 1400mA.
2100mA- This is the best option if you’re on a budget. It reduces the number of COBs you need because you're driving the LEDs harder. It won't be quite as cool or efficient as 1400mA but is still a huge reduction in heat and electricity consumption over HPS. Make sure you have some active cooling if running your COBs at ~75W+.
How much wattage/how many COBs (36V VERO29 or CXB3590) do I need for my space?
2' x 2': 150W required for full coverage. For example 4 COBs @1050mA, 3 COBs @1400mA, or 2 COBs @2100mA.
2' x 4': 300W required for full coverage. For example 8 COBs @1050mA, 6 COBs @1400mA, or 4 COBs @2100mA.
3' x 3': ~340W required for full coverage. For example 9 COBs @1050mA or 7 COBs @1400mA.
4' x 4': 600W required for full coverage. For example 16 COBs @1050mA, 12 COBs @1400mA, or 8 COBs @2100mA.
Which 