Lighting LED Terms, buying guide, and faq

[Atulip]

So I see a lot of questions regarding LEDs, and most answers are somewhere, scattered around the web. I took an interest to LEDs recently, trying to answer all the questions I had. How they work, what makes one light better than another, what spectrum is best; a lot to try and research.


I'm gonna try to get down everything necessary for understanding leds on the market today. And understanding how much light they actually produce. If anyone thinks something should be added, or if anything is incorrect, let me know. This is to the best of my understanding of the terms and math.

Common LED terms

LED - light emitting diode. Works on electroluminescence, a material that emits light from electricity.

COB - chip on board. Multiple diodes in a single chip.

Mono - Single color leds, used usually to refer to single diode chips.

Spectrum - the distribution of light at different wavelengths.

Watts - a measurement of energy usage. 1 watt = 1joule/second. Kilowatt hours or kWh is how you're usually charged on your electric bill, or 1000 watts used for 1 hour.

Nanometer - unit of measurement for light wavelengths.

Color - used to describe the appearance of white light in kelvins. Usually ranges from 2700k, a warm yellow glow, to 6500k, a light blue color.

CRI - how closely a light matches the spectral distribution of the sun.

Lux - a measurement of light, adjusted to how the human eye sees it.

Lumens - the average lux a light source will emit over a square meter.

PAR - photosynthetic active radiation, light in the 400-700 nanometer range. Often measured in ppfd

PPFD - photosynthetic photon flux density, a measurement of the photon density of a specific area. A measure of photon count.

PPF - the average ppfd a light source will emit over 1 square meter. Plant equivalent of lumens.

Photon - A quantum measurement of light (as both a particle and a wave)

Micromole - how we measure photons. Seen as µmols or often "umols" improperly.

Driver - or power supply. The AC/DC converter for Led strings.

Beam angle - to describe the spread of a light source or optic. References the point where 1/2 the light level of the center would fall.

Optics - used to direct light or adjust the spread pattern.

Lens - cover the diode, type of optic. May adjust all light emitted from the led.

Reflector - outside the diode, adjusts the outer area of the leds beam angle.

Diffuser - over the diode, usually to increase spread and limit hot spots.

Lumen maintenance - rated hours for lumen depreciation, typically LM70, or the hours where light output wound be 70% original intensity.

LER - luminous efficacy of radiation. The amount of lumens produced from 1 watt of radiation for a given spectrum.

QER - quantum efficacy of radiation. Same as LER, but with photon measurement in the 400-700nm range.

 

[Atulip]

This guide is meant to help buyers determine how much led light they need. Whether replacing current light with more efficient light, cutting down on high canopy temperatures over HID, or just determining the right amount of light for your space.

If you haven't yet, look over the terms, I'll be referencing them from here on.

First determine how much light you want. Is this a dedicated flowering area, just for clones, trying to grow trees? More light does not scale linearly with yield, though. Meaning a lower overall light level will yield more efficiently than a higher level. But having not enough light, quality may suffer.

A helpful chart, provided by the owner of tasty led, mapped from photosynthetic response at different intensities.

Here's where a little math becomes necessary. Most quality led companies will provide you with data on the PPF output(the average ppfd over a square meter) of their light. It's easiest to start with PPF when comparing lights.


If ppfd of a specific area is provided instead, we simply need to multiply the ppfd by the area in square meters. For example, I purchase a light designed for a 2'x4', so the ppfd of that area is provided, rather than the ppf output. It has a ppfd of 850 in .75 square meters, so the light has a PPF of 637.5 (850*0.75=637.5)

Or electrical efficiency at the wall may be provided as µmols/j, multiply this by the wall wattage to get the PPF output. For example, a 250w light with an electrical efficiency of 2.1µmols/j would have a PPF of 525.



Par Watts may be provided. You would then multiply this by the QER of the spectrum for the PPF.

Hopefully one of these is provided, but if not, total lumen output may be provided. This is OK for comparing 2 lights of the same source, but for comparing different spectral distributions, and determining our PPF we'll need more math.

Here we'll want the lumen output of the source, divide this by the LER of the spectrum to get the par watts then multiply by the QER of the spectrum to end with PPF output.

Once we have PPF output, we can use it to work backwards for PPFD or µmols/j. Efficiency in µmols/j is useful when comparing the efficiency of 2 different lights; simply divide the PPF by wall wattage to get the efficiency in µmols/j.

For example, 2 lights, one with a ppf of 700 for 300watts, one with 800 for 400w. The 300w light is 2.33µmols/j and more efficient, the 400w light would be only 2µmols/j.

PPFD is what we're interested in when deciding for our space. Reference the chart above for an idea of what to aim for. Given the PPF, we simply divide by the square meters of our space to get the PPFD.

500ppf in a 2'x2'(4/10.7=0.37sq meters) is 500/0.37 = PPFD of 1351.

Now we have an idea of how much light we need, and determining if an led will provide that, but what if we just want to replace an existing light? If it's LED we should know the PPF and that's easy to compare. But what if it were an HPS we wanted to replace. That can be calculated too.

I like to reference hortilux, I believe it's still the best for Single Ended HPS. It's known that a 1000w hortilux super hps is 145,000 lumens total output and has a PPF of 1798. We need both of these numbers to compare different bulbs, as they have different efficiencies.

Given the PPF of 1798 and divided by the total 145,000 lumens, we come up with .0124 as a conversion for HPS lumens to PPF. 88,000lumen 600w HPS has a ppf of 1091(88,000*.0124=1091)

Now the fun part. We need to go one step further to figure out how much light we have on the canopy. Since light is still measured in a 360° sphere, we only know the PPF of the unreflected bulb. The reflector determines how much light gets corrected and sent downward to the canopy. And how well the light is spread. Around 25-30% loss usually what's attributed to estimate canopy PPF.

Our 600w hortilux with a PPF of 1091 becomes 818 on the canopy with a 25% loss to reflection. The canopy PPF is the number we want to compare to.

And when comparing a larger single source light to multiple smaller sourced ones, we can also give the single source another reduction, to account for the poorer spread. Maybe 5-10% here.

The PPF of 818 becomes 736 if we gave it a 10% handicap to account for the better spread of say 4 smaller lights.

I was including average bulb wear, but that doesn't make as much sense to include now that I think about it. Average bulb wear was added into the reduction to account for most people replacing their bulb at ~2000 hours, so it saw an average of 5% wear, 100% when new, down to 90% when replaced. But LEDs also emit less light over time. High quality, around 10x as long as HPS for the same 90% output, but the average bulb wear should apply to led the same way. So you'd need to handicap them both when comparing.



It may seem like a lot of math, but once learned it's very useful for spotting out the crap in the market. Like replacing a 400w HPS with an 180w led, or replacing a 1000w with 450w, or a 250w with 75w. Now that we can calculate what an HPS produced to compare, some of these claims start to look impossible. We can compare to their PPF, if they provide it.






Bonus, beam angle math. Beam angle is useful for finding the area a specific light should cover at a given distance. Beam angle determines the point where 1/2 the light output from the center falls.

This is where I prefer an online calculator. Input 1/2 of beam angle for angle beta, distance from canopy as side a, and side b will be the distance from the center where 1/2 the light intensity falls.


http://www.mathportal.org/calculators/plane-geometry-calculators/right-triangle-calculator.php

For example, a light using 60° lenses, hung 24" from the canopy, we would input 24" for side a, 30° for angle beta, and solve for side b. Answer being 13.8". So at 13.8" from the center, we would find about half the intensity as directly under the source. And estimate that the light would evenly cover a 2'x2' - 2.5'x2.5' space at this height.

 

[Atulip]

FAQ

What if an Led company does not provide PPF or a way for me to calculate PPF?

I usually assume they're at the lowest efficiency, and treat it like a watt for watt equivalent to HPS at best, but you could inquire with them to find out if they will provide that information. There's no reason for a company to hide this information from customers. At a minimum a company should be able to provide a calculated PPF based individual manufacturer led chips used and drive currents. There's no secret sauce, led manufacturers provide data for their chips...

What about build quality, warranty, etc?

This is where you'd need to find reviews, or grow journals. Try and find people who aren't just reviewing a recent purchase(everything looks great when it's new), or reviewing free products(who doesn't like free stuff).

For warranties, consider how long you even want to keep the lamp. You probably want to replace most leds in the 15,000-20,000 hours area. Or 2-4 years, depending on 24/0 lighting to 12/12 lighting. No need for that 10 year warranty, you'll have a dim heater by then.

What about brand of leds?

Brand doesn't matter too much, theirs some quality in them all. But generally epistar panels are your budget leds, treat as a watt for watt equivalent. Cree/osram/Samsung/Phillips make quality monos, but there are bins of chips. Lower bin chips are less efficient, so an led grow light may still use budget low efficiency chips and advertise "Cree". This is why it's important to find the PPF, not just look for a brand chip.

What about Cob lighting?

Just a more efficient light source on the market currently. It takes advantage of high efficiency blue dies, crammed together in a single chip platform, they then excite a phosphor coating which changes the spectrum to appear white.

I saw a video with a guy and a par meter, is this the PPF?

No, this is merely a single point reading, usually only done in the center, and often used with narrow optics to raise the center value. I'm sure there's a way to calculate PPF from this number, used with height, beam angle, and light emitting area, but I'm far too high for all that crazy math.

There's no reason for a company to provide you only with a single point center par reading, unless you only plan on growing in that exact spot...

An example where a narrow beam reflector is used. At this hanging height and beam angle, the light only covers a 2'x2' area. The narrow optic was used to concentrate the light to the center more, allowing for a bigger reading. With this hanging height, we'd want a 90° angle or greater to effectively cover a 4'x4' from this height, though the lux reading doesn't look as high then.




Imagine only going by the center par number in this example. It almost looks like as good as a 1000w HPS! But it's most definitely not enough light for a 4'x4' as advertised.



What about spectrum?

That's still up for debate, but the Mcree action spectrum is still the most accepted. Don't buy into myths that plants don't use green light, they do, just at a lower rate. A lot of us are finding out now that green light plays a large roll on lower plant health.

 

[Atulip]

ROI or Return On Investment calculations.

The math needed to compare 2 light sources cost and the hours of operation needed to see an added startup cost. (IE when does a light pay for itself in electrical savings)

First we need the PPF of the light and the wall wattage. We'll use that to get the electrical efficiency at the wall. (PPF/watts = efficiency in umol/j) and we'll want the cost of the unit, divided by the watts to get the cost/watt.

For example, light A offers us a PPF of 720 for 340w at the wall and costs $700. 720/340 = 2.12umol/j, 700/340 = $2.06/watt

Light B offers a PPF of 575 for 440w and costs $250. 575/440 = 1.31umol/j, 250/440 = $.57/watt


Once we have the umol/j and $/watt, we can compare two lights. First take the efficiency of the more efficient light, and divide by the efficiency of the other. This is our wattage factor(the less efficient led requires more wattage for the same light output).

Continuing the before example. Light A with 2.12umol/j divided by light B with 1.31umol/j gives us a wattage factor of 1.62. Meaning Light B requires 1.62x as many watts for equal output of Light A.

Now that we have the wattage factor we can compare costs. Light A remains the same, $2.06/watt, Light B becomes $.92/watt, making the adjusted price difference between the two lights $1.14. This is the extra cost we're paying for more efficient light.

With the adjusted cost per watt difference, $1.14, we need to compare the operating costs, or electrical costs to run each watt hour, adjusted to the same watt factor. Using the US average of $.12/kWh below,

Light A costs $.00012/watt hour to run.($.12/1000) light B, since it requires 1.62x more wattage, costs $ .00012*1.62 = $.000194 per watt hour. Then we simply take the difference, .000194-.00012 = $.000074 more per hour to run Light B.

Now we just go back and take our adjusted cost per watt difference, $1.14, and divide by the adjusted watt hour cost difference, $.000074. 1.14/.000074 = 15,405 hours.

Light A will require 15,405 hours of operation to see your ROI over the less efficient, cheaper option of light B. Then simply divide by daily hours, 18 hours for example. 15,405/18 = 856 days. And you could divide by 365 to get years, 2.34 years for return on investment at 18/6 and US average of $.12/kWh.


Other costs to consider. Cooling costs. 3.4BTU/hour of heat generated per watt of energy. Using the same watt factor, 1.62, light B becomes 5.5BTU/hour heat. Difference being 2.1BTU/hour per watt. Calculate the cooling cost per BTU, for example a 5,000 BTU AC that draws 552w. 552/5000 = .11watts per BTU/hour cooling. Add this to the wattage factor for additional cooling wattage.

Same can be applied to bulbs. A $75, 1000w bulb that needs to be replaced every 2000 hours. $75/1000 = $.075 per watt for 2000 hours. $.075/2000 = $.000375 per watt hour. Add this to the operation cost per hour of the light before taking the difference.

 

[tobe]

@Atulip
Great read thanks for all these infos.
cu tobe

 

[F.N.]

A-tulip how did you figure out the btu rating between light A and B just curios bro. Could you figure out and equation on amount differnce one should get in weight of end dried product between light A and light B my man if using identical strain and pheno CHEERS

 

[Atulip]

1 watt of radiated energy(1 wall watt) results in 3.4BTU/hour heat. Though direct heat can be calculated with electrical efficiency times wattage. A 50% efficient led turns 100 watts at the wall into 50 watts light, and 50watts direct heat. But the light energy will be transformed to heat in the end. So 1watt = 3.4BTU/hour heat.


In equal conditions, the more light the more yield. But the less light will be a more efficient yield. (Easier to get 1gpw with a 400w HPS in a 1m2 than a 600w HPS in a 1m2, though the 600w would yield more). With the exception of light saturation. There is such a thing as too much light, usually from blue heavy spectrums. But no I couldn't say a specific yield. With proper lighting(ppfd of 700-900), a good grow, expect 500g/m2.