How to Choose the Correct LED Light for your Grow Environment

[Jack Aaron]

Hello,everyone in 420. I would like to talk about how to select an LED grow light here. Here are several tips and hope everyone here could give me some advice.

Adjustable Output Spectrum
Because LEDs are dimmable, an LED solution should let the grower tailor the light output spectrum. Look for an LED light that provides individual brightness controls for each color of LEDs. By varying the output power of individual colors, the grower can simulate seasonal light changes over a multi-week growing cycle.

For example, more blue light mimics the summer sun (vegetative phase), and more red light simulates the sunlight in the fall (flowering phase). This type of spectrum change is similar to the effect achieved by starting plants under MH lamps for vegetation and then changing to HPS for flowering. Growers can even tailor the light spectrum to suit individual plant type.

High-Power Cooling System
Like the CPU in your PC, high-power LEDs must be cooled with a heat sink and fan. Because high-power LEDs do not radiate any heat, the metal pad provides the only path for heat to leave the LED. Heat flows from the LED die, through the metal slug, through the circuit board, into a heat sink and then out to the surrounding air.

Look for LEDs mounted on a metal-core printed circuit board (MCPCB), a space-grade technology used for operating electronics at high temperature. An MCPCB conducts hundreds of times more heat compared to the typical fiberglass circuit board. An MCPCB is required for the high power levels that LED horticultural lights endure.

Finally, make sure the MCPCB is mounted to a large heat sink, preferably one with many fins. More fins provide more surface area to dissipate heat into the surrounding air. The heat sink should be cooled by multiple fans to prevent a single-fan failure from damaging the LEDs. The light’s datasheet should list the fan’s predicted lifetime.

Constant-Current Driver Circuit
The electronic circuit powering the LEDs is an important consideration when evaluating LED lights. The LED “driver” circuit is like an HID ballast; it converts AC input power into DC power at the proper voltage and current level for the LEDs. Its most important job is supplying a constant DC current even as the LED voltage changes over time and temperature.

Many simple driver circuits provide a constant voltage, meaning the output current varies with the LED voltage. A constant-voltage driver can cause early LED failure. As the LED’s temperature increases, its voltage drops, causing a constant-voltage driver to supply more current in response to the decreased LED voltage. This feedback loop results in a runaway current that destroys the LED.

Proper LED driver circuits supply a constant DC current, holding steady as the LED voltage changes with temperature. Look for the words “constant-current” in the horticultural light’s LED driver specifications.

 

[Icemud]

Hello,everyone in 420. I would like to talk something about how to select an LED grow light here. This are several tips and hope everyone here could give me some advice.

Good write up and information! Kudos!

I do want to comment on the spectrum controls. I don't believe this is a absolute necessary "have to have" thing on grow lights, at least now and for probably the next 5 years or so. The reason is, that light spectrum for plants is very very heavily debated, even with science abstracts conflicting each other, and with every plant species being different, even some phenotypes lighting needs differ, I don't see spectrum control as a necessary thing until plant lighting, photomorphogenesis, receptors and pigments are understood more from the science community.

Now with that being said, dimming controls are nice for 2 reasons, One you can save electricity when the extra intensity boost during vegetative stage is not needed, and 2 for the reason that you mentioned with constant on circuts. Most dimming LEDs use PWM or Pulse Width Modulation, which is basically turning the LED on and off at very high speeds/cycles therefor allowing for optimal brightness, but helping to save the life of the chip.


A few other mentions of things to look for when selecting a grow light: Hope you don't mind me adding to the topic since I too am an LED enthusiast


Company history, product reviews and customer service:
We have all been there, or at least most of us, where we buy a product that looks awesome, only to find out the product is junk, and when it breaks you have to jump through many hoops to even get replacements or have warranties accepted. I advise anyone who is buying a grow light to consider the company, how long have the been in business, what are their warranty policies, how many people are already using the products with good reports/reviews, and if something breaks, how do people rate their customer service. Over the 4 years I have been here at 420 Mag, I have seen handfuls of LED companies come and go, many even within the same year they started so it is very important to know who you are buying from and if they are reputable. Also, I have seen many websites that have the title "10 best LED grow lights" or something similar... STAY AWAY from these as resources, and go to forums like 420 mag and others with actual growers with real word reviews. I have read just about every one of those "top 10" reviews and they are just paid advertisements and have poor information. Also like OP said, LED light brands that use reputable 3rd party testing from universities, colleges, labs and other data based or evidence based testing are much more reputable.

What is the actual coverage area

This is a big one in my opinion, as I have viewed probably 90% of the commercially available LED grow lights websites on the market, I find that almost every single one of them overestimates their lights footprint by quite a bit. The best way to find the actual footprint of a particular light, is to see PPFD or PAR readings over a 4'x4' grid, with a reading at every 1/2' or 1' mark on the grid. Since PPFD (photon count) is directly related to the process of photosynthesis, it is by far one of the best ways to make sure a light will be sufficient for your grow area. This is especially important with LED's because they are very directional lights and many of the LED's on the commercial market pack many chips in a small array which creates an insanely bright/intense area in the 1'x1'x area under the light, but if you move out 2' from the center, with many of these lights you are lucky to be able to even get a good bud.

Typical guidelines for what to look for: (for cannabis) other plants have other light requirements and it is best to check the plants DLI or Daily Light Integral to know how much light your plant needs.

24/0 schedule should have a PAR meausrement of at least 255 micromoles/m2/s-1
18/6 schedule should have a PAR measurement of at least 381 micromoles/m2/s-1
12/12 schedule should have a PAR measurement of at least 510 micromoles/m2/s-1

Most growers for flowering tend to prefer at least 800 micromoles/m2/s-1
If you are using supplemental co2 then you can go up to around 1500 micromoles/m2/s-1

*****if you do not add extra CO2, you should try to keep your PAR measurements under 1,100 umols/m2/s-1 because this is where extra light can actually slow growth instead of speed it up. Plant metabolism is reliant on 3 things, temperature, light intensity, and available CO2. If all 3 are in perfect sync, plant metabolism is high, but if one is lacking the plant will slow down to the rate of the variable out of sync, therefore you may not be achieving the best you can.

Now these numbers DO NOT mean just a center par reading, you want to see a nice uniform coverage where the entire grow area is receiving these readings... not just the center. So this is why PAR readings over a 4'x4' grid are very very nice, because the grower can get an idea of how a particular light will work with their garden.

I do see many growers saying things like "use 35watts per square feet" or "I use 80watts per square feet". The reason why this is wrong is like I explained before, LED are very directional and many times have hotspots under the light only to have intensity fall of greatly outside of the light perimeter. IF you judge your lighting by wattage, it does not tell you in any way how this light will fall into your canopy, and has no direct relation to plants. PAR and photons do have direct relation with plants, matter of fact it takes about 8 photons to be absorbed to break apart 1 molecule of CO2, so by "counting photons" which is what a PAR meter does, you can directly see how a light will provide power to your plants systems.

Diode brand

This is not as important as the other topic areas to consider, but it also is deemed worthy to know. I'm sure you have heard of brands that make LED's like Cree, OSRAM, Epistar, Epiled, Bridgelux, LEDengine and others. There are big differences between the Chips that are used in lights which is why it is important to consider.

Most LED grow lights use Epistar, bridgelux and Epiled (generic) diodes to assemble their lights. I would assume about 90% of the lights you can buy right now feature these 3 brands. Although they work well, and serve the purpose as intended, they also do have a difference from other brands such as OSRAM, and Cree.

Lumen Maintenance
Lumen maintenance is the ability for a chip to be used for a long time, and how long it takes for the light to lose "X" percent of its output. Eventually LED diodes wear out due to heat, phosphor coatings and other factors so its good to take the Lumen Maintenance into consideration when looking at LED's. Lumen maintenance is usually written in ways like LM90 or LM80 followed by an hour rating like 50,000 hours or 100,000 hours. What this means if you saw a LED chips LM80 40,000 hours, is that after around 40,000 hours of operation, the LED chips will lose 20% of their original intensity, or in other words only will put out 80% of the original intensity in this duration. Now each brand of chip differs in the LM, but generally certain brands (when cooled correctly) will last longer than others.

with most Datasheets and LM reports I have read, the best chips include Cree, OSRam, which usually will last about 60,000 hours or more losing less than 10% of their light, where as Epistar, Bridgelux, Epiled and LED Engine usually have a LM80 of around 34,000 hours (depends on the chip) but what this basically says is that a better chip will last longer, and give more light out for a longer period of time than a cheaper brand chip. So for those who invest in LED as a long term investment, you may want to consider the brand chips you are using.

Now on the flipside of this, there is Haitz's law which says that on average about every decade, technology will increase light output by 20% and cost per lumen comes down by a factor of 10. So with this in consideration, if you are choosing a LED solution, do you want to spend more for good brand LED diodes that will last the test of time, or do you just want to buy LEDs that you can get 3-4 years out of and then just replace with another cheap option. This is the growers choice, but well worth considering.

For this information, you should check with the LED manufacture to see if this information is available. Most LED companies don't like to share this information so you may need to investigate a little on your own, but those companies who do disclose their chip brands, have much more transparency to their customers and usually can be trusted more because their data is backed by testing.

*** also in most cases the better brand led's like cree and osram also usually have better lumen/watt ratings, meaning that you get more light for an equal wattage used over cheaper LED brands. This is not true for every chip, but almost every chip I have encountered this has been true. This is also dependent on the BIN the chips were in. A BIN is a way the chip manufacture sorts chips by color rating/wavelength, and also intensity. You could have the same type of chip on a top bin putting out 89lumens/watt but the same chip in a lower bin could only be delivering 50lumens/watt. Even though BIN is very important in selecting a LED light, almost every single LED company I have come across does not share this information, and most are clueless what actually is in the lights they sell. A lot of these LEd companies buy their lights at a wholesale price from a manufacture in china, slap a brand on it and sell it for 5x the actual cost. This is the reality of the LED market, so if you find a company that actually shares their BIN, then you know they probably had a good amount of input on the design of the light. Companies that do not share the BIN of their led's either are clueless because they are just a company buying already assembled lights, or they do know the BIN, but hide the information because they use low BIN numbers, but charge a premium price.

**** Higher BIN chips cost more than lower bin chips.
**** better LED chips like osram and cree cost about 4-6x as much as epistar and other generic led chips. This is why the price of LED grow lights that use better brands usually are much higher in cost.


Heat reduction

I see many many growers that switch from HID lighting to LED lighting in search of a cooler grow area temp... but is this really true. I have done a good amount of research in this area and following the laws of physics, equal wattage used = equal heat load. So all the companies that claim LED's are cooler are pretty much lying to you. You cant have a light that produces less heat with equal wattage, it goes against physics. Now some people have noted that LED's seem to run cooler than HPS and typically this is because with LED you can get away with slightly less wattage. Now companies that claim 50% less electricity are full of it and lying, but I would say its safe to say you could reduce electricity by about 20-30% which in turn would lower the temps. This is the only way that an LED can produce less heat. Like the OP described, LED lights do not put out radiant heat (IR) but they do put out a lot of heat through the back side of the LED, which is why optimal cooling and heat management is necessary. However Light when absorbed turns into heat, and if you don't believe me, feel your floor outside your grow area, then open your grow tent, let the light hit it for 20 minutes and feel the floor again, it will be hotter. So if you add up the heat from absorbing of light, plus the waste heat out the back of the LED, at equal wattage it will be the same no matter what the source.. For example 1000w HID = 10x 100w LED = 100x 10W bulbs in terms of heat added to an area... Therefore don't be fooled by claims of less heat.

Now there are things that may lead the effect on your grow environment to show differences, such as the materials that surround your grow area and what they are made of, but generally speaking, LED's are NOT cooler than HID.

Another thing I want to touch on here is that LED's do not have a way to directly vent the heat out of the grow area like air cooled hoods for HID, which I have found that LEDs actually heat up my grow area MORE than HID with air cooled hoods. So also consider this when purchasing.



Well this is all I can type at the moment because my eyes are heavy and its late, but I will add more as I think of other things you should consider when buying LEDs.

 

[JBUptown]

I agree with most of your comments concerning LED, but I must ask for some clarification regarding your section on Heat reduction.

Theory: equal wattage used = equal heat load

How did you conclude that direct static relationship?

As this is applied to horticultural illumination ... Are you saying that all horticultural illumination technologies produce the same amount of heat in the direct proportion to the value of electricity consumed?

Best Of Buds

JB

 

[Icemud]

I agree with most of your comments concerning LED, but I must ask for some clarification regarding your section on Heat reduction.

Theory: equal wattage used = equal heat load

How did you conclude that direct static relationship?

As this is applied to horticultural illumination ... Are you saying that all horticultural illumination technologies produce the same amount of heat in the direct proportion to the value of electricity consumed?

Best Of Buds

JB

1 watt at luminaire = 3.4128 BTUs per hour

The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. The first law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings

So in a perfectly "isolated environment" the above shows that equal wattage, equal heat as heat is the lowest form of energy.

Now none of us grow in a "isolated environments" so even thought the heat load would be the same, the environmental influence would effect how the heat is transferred to surrounding areas based on the materials surrounding the grow area and the spectral absorbance of the particular material.

 

[Spitz]

Amen Icemud

 

[JBUptown]

Hi IceMud,

I understand Physics, I earned a gold star in college!

Sorry, just trying to keep it light ...
I realized when I just read my post from yesterday that it could have been interpreted as not respectful, far from my intent. I'm not a disagreeable troll trying to start a forum flamer, especially with you! When it comes to growing Cannabis, you have my utmost respect. Your knowledge, advice and sharing of information on 420Magazine is useful and needed. I have learned much from about a dozen or so folks on this site the past few years, and you are one of that group of folks. I thank you for your efforts to share your knowledge and experience, much appreciated! ABSOLUTELY no disrespect is meant or tendered.

I'm am trying to understand your statement regarding LED, HID and heat. I think I interpreted your statements as LED does not emit less heat (BTU, Joules, or whatever unit of measurement is used) than another illumination technology given the same wattage draw. Heat emitted will be equal if drawn wattage is equal. You then conclude that HID runs cooler than LED in your experience.

Here's my struggle, please help me understand ...

It seems you are stating that all horticultural illumination technologies emit the same unit of heat in direct proportion to the unit of electricity consumed? Have I misinterpreted your thoughts and statements?

If true, then HID, HPS, MH, LED, CFL, FL, Incandescent or Induction illumination technologies should all emit the same values of heat directly proportionate to the wattage drawn (converted).

I truly appreciate your input and knowledge, thanks for taking the time to inform and share.

Best Of Buds
JB

 

[Icemud]

Hi IceMud,

I understand Physics, I earned a gold star in college!

Sorry, just trying to keep it light ...
I realized when I just read my post from yesterday that it could have been interpreted as not respectful, far from my intent. I'm not a disagreeable troll trying to start a forum flamer, especially with you! When it comes to growing Cannabis, you have my utmost respect. Your knowledge, advice and sharing of information on 420Magazine is useful and needed. I have learned much from about a dozen or so folks on this site the past few years, and you are one of that group of folks. I thank you for your efforts to share your knowledge and experience, much appreciated! ABSOLUTELY no disrespect is meant or tendered.

I'm am trying to understand your statement regarding LED, HID and heat. I think I interpreted your statements as LED does not emit less heat (BTU, Joules, or whatever unit of measurement is used) than another illumination technology given the same wattage draw. Heat emitted will be equal if drawn wattage is equal. You then conclude that HID runs cooler than LED in your experience.

Here's my struggle, please help me understand ...

It seems you are stating that all horticultural illumination technologies emit the same unit of heat in direct proportion to the unit of electricity consumed? Have I misinterpreted your thoughts and statements?

If true, then HID, HPS, MH, LED, CFL, FL, Incandescent or Induction illumination technologies should all emit the same values of heat directly proportionate to the wattage drawn (converted).

I truly appreciate your input and knowledge, thanks for taking the time to inform and share.

Best Of Buds
JB

Hey JBUptown.

No disrespect taken at all and hopefully my post didn't come across that way either. From everything that I have studied, and maybe you can teach me, it seems that all electrical appliances that do work, add the same heat load based on the wattage draw. (I may be incorrect but so far everything I have read has supported this, but I am open to being wrong too

The reason I mentioned that HID runs cooler than LED is based on air cooled HID, which give a pathway for heat to be directly vented from the grow environment before it can add heat, where LED vents the warm air into the grow environment with no means of direct extraction. Now if comparing a 400w LED vs 400w HID with no air cooled hoods or means of extraction, then theoretically the heat load should be the same (in an isolated and sealed environment, where no energy were to escape of be transferred).

Now since none of us have sealed enclosures that would prevent heat exchange, then there is the environmental influence. Such as LED does not emit radiant heat, but HID does, so depending on the type of material that your grow area is made up with, this can either block IR radiation such as the silver mylar, or if you had white paint which reflects visible light but absorbs IR radiation, then this would allow for heat transfer outside of the grow environement allowing for differences in tempurature inside the enclosed area.

At least thus far this is my understanding of it. but I am completely open to being educated too

I definitely want to make sure that in know way I took your info as disrespectful or trolling and I hope you didn't see my response that way either we are all here to learn, and since I don't have a degree in physics, there may be others that could say I am wrong. This is just based on the research I have done on this.

Either way I very much appreciate your kindness and interest in discussion and I definitely respect your input as well

 

[scruffy420]

1 watt at luminaire = 3.4128 BTUs per hour



So in a perfectly "isolated environment" the above shows that equal wattage, equal heat as heat is the lowest form of energy.

Now none of us grow in a "isolated environments" so even thought the heat load would be the same, the environmental influence would effect how the heat is transferred to surrounding areas based on the materials surrounding the grow area and the spectral absorbance of the particular material.

I'm not trying to preach or "teach lessons" here, but I think that you are using the equation in this post incorrectly. The watts to BTU conversion is a conversion of power and energy. Energy is a property of matter (yes, just like inertia is - Thank god for Bill Nye, that sly science guy). Power is the amount of energy used/transferred per unit time. So, when you compare watts to BTU/hr, that is only a conversion factor. That doesn't mean that if you light draws 1 watt of power, it generates or gives off 3.4128 BTUs of energy as heat. It IS drawing 3.4128 BTUs/hour from your outlet, but the energy it is pulling from the wall is being "used" in a few different ways. Part of that 3.4128 BTUs is converted into light energy (which you can hopefully tell, because if not, you need a new light; yours is broken). This "isolated environment" that you mention is often referred to as an "ideal system". We live in the real world, and therefore there ARE losses of part of that energy, as you also indicated in your post. This is given the term "efficiency", which I'm sure everyone who reads this is very familiar with. Efficiency would state that since we do not and, by definition, cannot have an "ideal system", we MUST have an efficiency rating. So, what we actually have to compare is the efficiency of each light source. HID lighting operates at insane temperatures, which all growers probably know. The heat that is given off is a direct function of the power drawn by the light itself. As you can probably guess, that heat has to come from somewhere, in this case, your electricity bill. Much of the energy that the HIDs use is converted into heat since the light is essentially "burning" material to produce the ungodly bright light that those lights do. If it doesn't heat up the material enough, it won't glow, and therefore will not give off the light. LEDs work differently, however. LEDs do not "burn" material to produce their light. 5 years ago, I probably could've explained exactly how LEDs work, but since then, I haven't studied them at all. Suffice it to say that LEDs are simply P-N junctions that require a minimum voltage to "forward bias", which allows current to flow across the diode, which causes the diode to give off light. Between the two lights, we can compare where the heat comes from, from the simple, yet apparently insanely drawn out explanation I'm giving here. I swear, this seems like it's taking forever to type. Anyway, the heat given off by the HID lights comes from the reactions of the light itself, and the power required to bring the material in question up to the temperature required for it to actually produce light. (This is why you will see your HID, yes even the headlights on your car, get brighter and brighter as it heats up, until it is finally at operational temperatures.)
The heat given off by LED panels is determined almost exclusively through the amount of current that runs through the panel. These heat losses are determined by the equation E = I(squared)R, which translates to energy = current^2 (times) resistance. Since diodes operate at low DC voltage and require very little current to flow to actually give off light, these losses are very small. Most LED panels operate in the 1-5 Amp range, if that. Total resistance can be fairly high, but most panels are probably wired in series as to reduce total circuit resistance. This still only calculates out to a few BTUs (the units that the answer to the equation above will be in ridiculous small units to include the electrical unit of charge the "coulomb" (sp?). Like I said, it's been like 5-5.5 years since I've studied any of this, but that is about the right basis to be thinking about it in.

Again, I am not trying to lecture anyone, it is just that energy is my job right now, and after I start on my degrees, it will be all that I do. I appreciate your time, and hope this post isn't too ridiculously long.

 

[Icemud]

I'm not trying to preach or "teach lessons" here, but I think that you are using the equation in this post incorrectly. The watts to BTU conversion is a conversion of power and energy. Energy is a property of matter (yes, just like inertia is - Thank god for Bill Nye, that sly science guy). Power is the amount of energy used/transferred per unit time. So, when you compare watts to BTU/hr, that is only a conversion factor. That doesn't mean that if you light draws 1 watt of power, it generates or gives off 3.4128 BTUs of energy as heat. It IS drawing 3.4128 BTUs/hour from your outlet, but the energy it is pulling from the wall is being "used" in a few different ways. Part of that 3.4128 BTUs is converted into light energy (which you can hopefully tell, because if not, you need a new light; yours is broken). This "isolated environment" that you mention is often referred to as an "ideal system". We live in the real world, and therefore there ARE losses of part of that energy, as you also indicated in your post. This is given the term "efficiency", which I'm sure everyone who reads this is very familiar with. Efficiency would state that since we do not and, by definition, cannot have an "ideal system", we MUST have an efficiency rating. So, what we actually have to compare is the efficiency of each light source. HID lighting operates at insane temperatures, which all growers probably know. The heat that is given off is a direct function of the power drawn by the light itself. As you can probably guess, that heat has to come from somewhere, in this case, your electricity bill. Much of the energy that the HIDs use is converted into heat since the light is essentially "burning" material to produce the ungodly bright light that those lights do. If it doesn't heat up the material enough, it won't glow, and therefore will not give off the light. LEDs work differently, however. LEDs do not "burn" material to produce their light. 5 years ago, I probably could've explained exactly how LEDs work, but since then, I haven't studied them at all. Suffice it to say that LEDs are simply P-N junctions that require a minimum voltage to "forward bias", which allows current to flow across the diode, which causes the diode to give off light. Between the two lights, we can compare where the heat comes from, from the simple, yet apparently insanely drawn out explanation I'm giving here. I swear, this seems like it's taking forever to type. Anyway, the heat given off by the HID lights comes from the reactions of the light itself, and the power required to bring the material in question up to the temperature required for it to actually produce light. (This is why you will see your HID, yes even the headlights on your car, get brighter and brighter as it heats up, until it is finally at operational temperatures.)
The heat given off by LED panels is determined almost exclusively through the amount of current that runs through the panel. These heat losses are determined by the equation E = I(squared)R, which translates to energy = current^2 (times) resistance. Since diodes operate at low DC voltage and require very little current to flow to actually give off light, these losses are very small. Most LED panels operate in the 1-5 Amp range, if that. Total resistance can be fairly high, but most panels are probably wired in series as to reduce total circuit resistance. This still only calculates out to a few BTUs (the units that the answer to the equation above will be in ridiculous small units to include the electrical unit of charge the "coulomb" (sp?). Like I said, it's been like 5-5.5 years since I've studied any of this, but that is about the right basis to be thinking about it in.

Again, I am not trying to lecture anyone, it is just that energy is my job right now, and after I start on my degrees, it will be all that I do. I appreciate your time, and hope this post isn't too ridiculously long.

Hey Scruffy, I appreciate your reply and I am definitely a man of long posts myself. Too much info to sum up in a short paragraph lol

Anyhow I completely understand what you wrote and I do agree that there is waste heat produced by all electronic components within a light system, however, if the total draw is the same, lets say 100W HID vs 100w LED, the heat load is still going to be the same regardless of efficiency. The reason for this is light is made up of photons, when a photons strikes a surface the energy is transferred to the surface, the surface vibrates causing friction and emits heat. So light all eventually turns into heat, with the exception it is driving a photochemical process in which it is stored as caloric energy. This is regardless of efficiency because lets say you have a HPS bulb and and LED. Typically a HPS bulb puts out around 30% light and 70% waste heat. Most leds are around 40% efficient which means they generate about 40% light and 60% waste heat. Now with either light, 100% of the energy used ends up as heat eventually in the enclosed area, because as stated, photons convert to the lowest form of energy (heat). So if you add the light generated heat produced by photon absorption + waste heat you get 100% of the energy used (wattage).

Therefore the formula which you can find on most HVAC forums for building construction and heat load from lamps is this:

Q-l= (W * 3.412) * Fu * Fs * CLF-h (sensible heat gain)


Q-l = Sensible Heat Gain (SHG) from lights
W= Lighting power output in Watts (Btu/hr = W * 3.412)
Fu= Usage factor or percentage of maximum design for each hour of the day
= 0 when all lights are off
= 1 when the maximum design number lights are on
0 <= Fu <= 1 Example Fu = 0.5 when 50% of lights are on.

Fs= Service Allowance Factor or Multiplier (accounts for ballast losses in fluorescent lights and heat returned to return air ceiling plenum in the case of air-light fixtures)

CLF-h = Cooling Load Factor (CLF) for given hour. This depends on zone type, total hours that lights are on, and number of hours after lights are turned on,



So now putting this formula in use with an example: Lets use 100w light source (doesn't matter what type) as this is total work/draw

Fu=1 since there is only 1 light and it is on (this is for installation of multiple lights in a room, and the factor if 1/2 are turned off)

Fs= 1 Since we are talking about a light hung in an enclosed/sealed area. There is no loss to ceilings or exchange of energy outside the enclosure. Also we are looking at total wattage draw, this also would be entered in the equation as a value of 1, as SAF is typically used to determine the difference between the rated wattage and the actual draw, accounting for the ballast and the usage of the light. Since we are using total wattage draw at the plug, this figure also is not necessary. An example where this would be used is if you were calculating the heat load of a room, based on the advertised wattage draw, but not actually taking the measurement, then different lights are given a Ballast factor in which accounts for the actual usage of the ballast separate from the light.

CLF-h = in our example we would not use Cooling load factor as this represents lost energy through a surface/wall/floor and the rate of transmission of heat energy. In our example we have a sealed enclosure with no heat loss, however if we wanted to calculate the cooling load factor of a certain material such as mylar or brick, then this would be a constant based on the material, but would not change due to the light type.


Q-l= (W * 3.412) * Fu * Fs * CLF-h (sensible heat gain)
Q= (100 x 3.412) x 1 x 1
Q= 341.12 BTU/hr

again as you can see, if we are dealing with total draw then efficiency or losses due to electronic components are not necessary for calculation. This formula is used mainly for building heat load calculation with lights, therefore when estimating a project and necessary cooling, then lamp wattages are used based off packaging and not actual draw, which is where Fs/SAF would then be added to the calculation.

So back to the original formula of heat load = wattage draw x 3.412

Irregardless of type of light, efficiency or electronics in the circuit, if you have 100w draw no matter if its an incandescent light, florescent, LED or HID, if wattage is equal, then the total heat load would be equal. Now as I mentioned in the previous post, how this light effects your grow area is dependent on other factors such as transmission of heat through conduction through building materials and grow area surroundings and this could be calculated as well, however, in an equal environment, with equal wattage, equal heat load is the result

Either way, I very much appreciate the input you gave in your post and I definitely understand what you wrote, but the only thing that you didn't consider was the heat from photon absorption added back into the total heat. Again I may be wrong, but I have researched this acrossed HVAC forums websites and standards handbooks, physics forums and websites, and even come across the same question in salt water enthusiast forums and flashlight forums, but it all leads to the same as the total heat load = heat produce from photons + waste heat.

 

[scruffy420]

With that being said, it occurs to me that I simply misunderstood your post. I took the post to say "since you have equal wattage lights, they must give off the same amount of heat (in the form of actual heat dissipation from the light due to the temperature of the light)", not that the total output heat (or power) for the entire light is the same. I completely agree with what your saying, as well, since it goes to provide even further proof for the first law of thermodynamics "energy cannot be created or destroyed, only altered in form". We were agreeing without even noticing All the energy that the lights draw from the wall MUST be used in some form, in which case efficiency is not useful, since we are considering the useful work of the light, as well as the wasted energy in the form of temperature rise and, therefore, heat dissipation. You are a gentleman and a cannabis-growing scholar; I applaud your style, and award you a 10/10! Keep on being awesome, man. Your grows are awesome.

 

[JBUptown]

Good discussion!
The "work" variable in the equation is what I so poorly omitted in the communication. My Neanderthalish missing link! I think Scruffy better said what I was trying formulate into a coherent paragraph or two, including my misinterpretation. Too much work and not enough off time, I can't wait for retirement.
So everyone vehemently agrees

It is just awesome that these kinds of discussions can be public and shared across the globe, so much has changed since I was a youngin. One of the "fun" purchases I have made for the grow stuff is a killawatt device, to track actual power usage of a particular product, compare results based on true power consumption and not what a label or sticker states as consumption. I'm a results kinda guy. It has been fun to tweak and get the best bang for the $ concerning energy illumination costs. Waste not want not!

Thanks for the lengthy discussions, much appreciated.

Best Of Buds

JB