All that matters is the heat from the fixture not get the leaves too hot. That fixture is NOT anywhere as powerful as they try to make it sound. It's a shame that buyers give vendors bonus points for being inefficient. Cannabis can easily handle 1500 µmol/m²/s. There is something very wrong if an LED fixture burns at 13". Watts don't mean a thing.
When reading Reviews of LED grow fixtures, I often see the term Watt used. Misused more than Used. When someone uses the term “True Watts”, I know they do not know. There is no such thing as a True Watt. True Watt is a marketing term. As with most marketing terms that use the word true or truth, it is neither.
An LED grow fixture has many Watts.
Wall Watts
Power Supply Watts
LED Driver Watts
LED Electrical Watt
LED Thermal Watt
LED Radiance Watt
If there were a Watt of importance it would be the Wall Watt. The main criteria for the evaluation of a grow fixture is how much electricity goes in, and how much light comes out. In this evaluation the amount of electricity is typically specified in Joules, as in PPF per Joule, not Watts.
More specifically than just the amount of PAR, what is more important is the amount of light phonton energy that reaches the plant leaves, PAR is measured in moles/m2/s, Watts/m2 /steradian, or Lumens/m2 /steradian.
Energy takes many forms in a grow fixture:
Photometric, Luminous Energy (Lumen Second)
Radiometric, Radiant Energy (Joule)
Electrical Energy (Joule)
Thermal Energy (Joule)
Photon Energy (Moles)
Each form of Energy listed above there are many more measures. Volume, Density, Intensity, Illuminance, Irradiance/Illuminance, and Radiance/Luminance.
Not to be, as often is, confused with Flux (moles/s), Intensity (moles/m3), Density (moles/m3/steradian), or Irradiance (moles/m2). Note about steradian: A steradian is a unit of volume. Because light spreads as it travels and takes on a cone shape, the steradian is used. The steradian is just that, the volume of a cone.
Photon Radiance is the number of photons (moles) hitting (incident) a surface area (m2) in a given amount of time (seconds) at a specified photon travel distance. If a vendor does not specify the height when using µmol/m²/sec and if using µmol/m² it also is nearly meaningless.
PPFD (Photosynthetic Photon Flux Density), is a measurement of Radiance, not Density. Why is it called Density? Because someone didn't think this lighting measurement was confusing enough? No, it is more likely someone was already confused enough that they used the term Density where it was actually Radiance. Happens all the time. PPF and PPFD are not standardized Units of measure. There is no standards body over seeing the technical characteristics of PPF(D). Anybody can use the terms however they desire.
PPFD measures the Transmittance of light. Transmittance being the effectiveness of transmitting the Radiant Energy.
Then there is the Quality of light. The Quality is the result of light Absorptance, Reflectance, and Photosynthesis. Quality is based on the Spectral Radiance. More specifically the Spectral Radiant Flux, in wavelengths (or frequency), received by the leaf surface.
As Watts relate to LED grow lighting, the Electrical, Thermal, and Radiant Watts are too dynamic to be meaningful in the evaluation of a grow fixture.
The Electrical Watts are divided in to a ratio of Thermal and Radiant Watts. A lighting electrical engineer will choose an efficient LED, with good efficacy, with the highest Radiance Watt to Thermal Watt ratio.
The most important parameter of an LED fixture, in my opinion, is the temperature of the LED. Secondly is the amount of current flowing through the LED. It is the temperature (and current) that gives LEDs their dynamic characteristics. It's the amount of current flowing through the LED and the fixture's thermal management that produces the LED's temperature.
When current flows through an LED a voltage is created across the LED's anode (in) and cathode (out). This voltage, referred to as the Forward Voltage, when multiplied times the current gives the instantaneous Wattage. I say instantaneous because it is so dynamic it will change.
When the LED Current flow is increased, it's Radiant and Thermal Flux increase. How much they increase depends on the LED's temperature. As the LED temperature rises the Radiant Flux decreases.
In grow lighting, the thermal management of the LED's temperature is the most important criteria in the fixture's design. Temperature is the number one factor in how much light is generated.
The Forward Voltage of a Red LED is about 2 Volts, a Blue or White LED about 3 Volts. While the LED Datasheet specifies the Typical Forward Voltage, there is nothing typical about it. The is nothing typical about any LED characteristic.
As the LED Current increases the Forward Voltage increases. As the Current and or Voltage increases the Wattage increases. As the Wattage increases the Thermal Flux increases and the temperature will likely increase, depending on the Thermal Management. As the Current raises the temperature the temperature lowers the Forward Voltage which lowers the Wattage. The lower Wattage decreases the Thermal Flux. Unfortunately the reduction in Forward Voltage is insufficient to cancel out the increased Thermal Flux and the temperature rises without significant Thermal management.
As the Wattage increases the temperature determines the ratio of how much of that Wattage is dissipated as light and heat.
Why this is so important in LED grow light fixtures is because Red (Deep Red 660nm) is the dominant LED Photosynthetic color.
Red light is produced by a particular type of LED or by converting blue light to red light using a phosphor converter. Most white LEDs are blue LEDs with a phosphor converter.
White and Blue LEDs are made differently than a Red LED. It's not important but LEDs are made using Indium, Gallium, Aluminum, as a Phosphide, Nitride, or Arenide. Blue LEDs are typically Indium and Gallium Nitride (InGaN). Red LEDs are Aluminum Gallium Indium Phosphide (AlGaInP) or Gallium Arsenide (GaAs). The point being Red and Blue LEDs are different in more ways then just their color.
The thing about Red LEDs is how much the temperature affects the Radiant Flux.
A red LED can easily lose 50% of its radiant flux to heat. And that is with half way decent thermal management keeping the LED temperature at or below 85° C.
U told him to FRY IT with both veg and flower on @ 6" ? Serious?
Unless you want liek teh Light Burnz
