How To Compare Grow Lights
Here i describe how to compare grow light systems, specifically LED fixtures as they are more confusing to consumers.
I highly recommend visiting my article on Light Measurement Systems to have a better understanding of the metrics used to quantify light and how they relate to grow light technologies.
How To Compare Grow Lights:
There is much confusion on what light metrics mean and how to use them to compare lights. This is a small guide to help growers understand and know what to use when comparing products.
PAR (Photosynthetically Active Radiation) is a region of the electromagnetic spectrum that plants can use for photosynthesis (400 to 700nm). PPF (photosynthetic Photon Flux) is the total amount of photons in the PAR region, emitted from a light source per second. This is different from PPFD (Photosynthetic Photon Flux Density) where only photons in the PAR region hitting a unit of area each second is measured. If you have a PAR meter, it is reporting PPFD (umol/m2/s) measurements. Many manufacturers know how confusing metric systems are to people, so it is very easy for companies to manipulate information to mislead the consumer in thinking their product is of high quality. However once you understand the differences in these metrics you will be able to cut through all the marketing and hype and simply ask manufacturers to provide the data you need to successfully quantify lighting fixtures.
Rule 1: Dont Use Electrical Watts To Compare Grow Lights
The actual power used by a light source is not a good indicator of a light fixtures performance, the efficiency of the light can vary widely among many products and will not provide any valuable infornation on the efficacy and efficiency. Many light products provide misleading information such as equivalent watts and some take it even further by stating the total combined wattage of all LED devices. This is very misleading as light emiting diodes are almost always run at much less than their maximum rated value.
Rule 2: Dont Use Equivalent Electrical Watts To Compare Grow Lights
Equivalent electrical watts can be skewed depending on how the manufacturer does the conversion or configures the measurements. Sometimes, more often than not, manufacturers even lie. Typically these values are exaggerated and do not produce anywhere near the suggested equivalent values. You must completely ignore these values as there is no standard method to these conversions or measurements and will provide a lack of consistency or realistic results.
Rule 3: Dont Use Lumens To Compare Grow Lights
A lumen is a photometric unit. Photometry was designed as a measurement system to better define our visual needs based off a unit value. Our eyes do not have a linear sensitivity across the visible light spectrum. As such we see some colors more easily than others. Using lumens to compare lights is a highly unreliable system for that reason alone. A light system can have high values of luminous flux (total lumen output) but yet still under perform compared to another with lower values. This is because the measurement system is weighted to our eyes and will show inconsistencies in what a light fixture can really provide. It is then best to ignore any metrics provided in photometry.
Rule 4: Dont Be Fooled By Magical Growth Spectrums
Many scientific papers have confirmed that all wavelengths from 400 to 700nm (PAR range) are used by plants for photosynthesis. However, many manufacturers still try to misguide the public and suggest that plants do not use any green light, which they do. They often compare their products spectrum to the absorbtion spectrum of free chlorophyll in a solvent. Which is irrelevant to land based plantation. Manufacturers do this to hide the fact that green LED technology is very inefficient and is the real reason why it is not used in light fixtures. Manufacturers are now starting to use white LED diodes as the current practicality and efficiency makes for an ideal choice for implementation.
Research shows that light quantity is more important than light quality. This is because the efficiency of each color spectrum is irrelevant because the quantum yield (photosynthetic efficiency) response is very identical over the photosynthetic bandwidth. Which means that the spectrum balance has a very minimal effect on plant growth.
Ultraviolet light has been shown to increase cannabinoids, specifically THC in cannabis. More research is needed but there is clear evidence on the benefits of UV supplimentation. However, UV has also been shown to negatively impact photosynthesis in leaves. So one must be careful how UV is used and to only use UV during the last few weeks of flower. UV is also very inefficient with LED technology. Infact, it is so inefficient that LED companies such as california lightworks, offer UV supplimentation with fluorescent tubes rather than UV LED.
Infrared supplimentation is another light product that is only useful for specific applications. It has been shown to reduce the total required amount of dark cycle in short day plants, by activating key photoreceptors responsible for photoperiodism. This means that a longer light cycle can be used such as 14/10, which will still induce and sustain the flowering process, while also increasing yields as a result of more light. However, the potential benefits of shorter flower induction may be outweighed by the additional cost of inefficient LED infrared diode supplimentation.
Rule 5: Dont Look At Single PPFD Measurements
Quantum PAR meters measure photons per unit of area, usually in meters squared. However quantum meters were originally designed to quantify solar radiation. Because its impractical to measure light with large sensors for units such as meters squared. Smaller sensors are used and then converted through mulitpliers to reach an equivalent value to that of a larger sensor. However this system assumes that light is uniform in all directions, which is only applicable to solar radiation. For electrical lighting, this system fails and what you instead get is a spot measurement that does not provide actual measurement values, but instead inflated values for what would otherwise be expected for solar radiation. This is highly confusing and manufacturers realize this and use it to misguide the consumer in thinking their light fixture is of high quality. For example, manufacturers can cluster LED's close together and use narrow beam optics, to present a extremely high PPFD measurement directly under the fixture. However these light levels will drop significantly as you move the PAR sensor just a small distance from the center measurement point. In order to obtain valuable data on a light fixtures output in PPFD, you need many more sample points over the entire area in order to calculate the average light level the system provides. This is still somewhat unreliable as most manufacturers do not provide this and the ones that do or information is available for, will need to have been performed under the exact same testing configuration as others. As such using PPFD is not practical for assessing a lights output capacity.
Rule 6: Dont Focus On The Wattage Or Brand-Model Of The Chips In LED's (Cree, Epistar, Osram, 1W, 3W, 5W, 10W, COB)
Do not focus on the chips used for LED fixtures, they are not a good denominator of how well a light fixture is going to be. Although choosing the latest technology would provide the designer the ability to build an efficient system, this does not mean it has been implimented that way. Cost must be taken into consideration and quite often the efficiency of the design is sacrificed to reduce these costs. As such, a designer will choose materials that fit into a design to provide the best cost effective product while providing as best efficiency for that price point. This means many types of LED chips can be suited depending on the overall intended design by the manufacturer.
Its commonly misunderstood that COB is more efficient than its SMD counterpart. This is incorrect however. Because of the concentration of energy from the many individual light emiting diodes, the heat actually works against efficiency. This is because the junction temperature is relative to a diodes efficiency. This is the main reason of how thermal runaway events happen. Think light blow outs. The same radiant flux output (total energy) of a COB chip, spread out over a larger surface area with SMD. Will be more efficient because of the lower concentration of heat and higher dissipation. However, their low price and simplicity make it a great option for DIY fixtures. Manufacturers will even use them in their light fixtures to reduce cost.
Rule 7: Request PPF, PPFD Maps And Input Power Values
Now you might have noticed that there are a lot of donts or do not. So you may be wondering. Well what do i use then ?. The simple answer is that there is only one system of measurement that you can use to accurately and reliably asses and compare lighting products. But unfortunately not every manufacturer provides this. And the main reason for this is simply because they know their product is not very good. So a good rule of thumb to know whether a fixture is competently made and can actually be compared to traditional technologies, are when they provide values in PPF (Photon flux). Not PPFD. PPF defines the total output capacity of a light source in its entirety. Measured using systems such as integrating spheres where all light is captured and quantified.
So for comparing light products, request photon flux values in PPF from the manufacturers to obtain reliable data on a light fixtures total output capacity. With PPF this will tell you how much energy in the form of photons a fixture emits per second. PPF is the single value which determines how much potential growth will be provided through photosynthesis. As said PPFD cannot provide information on a lights total output capacity, however information is sometimes available where several samples are taken over a typical grow area ( PPFD maps). This gives good information on a lights distribution pattern and uniformity quality. Also find or ask for the electrical input values, with this and PPF you can calculate the electrical photon efficiency. This tells you how efficiently the fixture turns electrical energy into usable light in the form of photons. This is done by taking the fixtures PPF value and dividing it by its electrical consumption (Actual power draw, not equivalents). For example. A 1000w DE HPS typically puts out 1700PPF with roughly 1000 watt consumption. 1700 ÷ 1000 gives you 1.7um/w or 1.7um per watt.
As always please comment your thoughts or any questions on the subject.
I dont know much about the cheaper LED products as they usually do not provide sufficient data to thoroughly quantify. I know most of the top commercial LED fixtures and actually have a list comparing them all including cost, photon flux, cost per umol etc.
Hortilux is a great bulb manufacturer so should get good performance from them. 1000w in a 5x5 is actually a little underpowered, so extra supplemental light will be beneficial here.
Yea, 1000W is actually better suited for a 4.5x4.5
1000w sodium discharge have a nominal efficiency of 1.3umol per watt. Which is 1300umol of photon flux (total light). You then take square footage of the grow area, and convert it into square meters (because all values of light measurements are in square meters). Which you then use to divide with the photon flux.
So 5x5 is 25 squares, convert that to square meters, is 2.322. Then take the flux of 1300umol and divide by 2.322. This then gives you an averaged value of photon density. Which is 559umols PPFD.
Ideally you want to shoot for 700umols, like with a 600w in a 4x4 is 740umols PPFD. This is due to the combinational effects of photosynthetic efficiency and reflection losses. Too much light in a given area and you are having to raise the fixture higher which adds reflection losses. Not enough light actually is fine for efficiency, you are just underutilizing the space available to you.
Using the supercharge setting might theoretically bring you up to 615umol PPFD. However, it would likely be less than that as they are not designed to run outside their rated value and would have lower efficiency as a result.
Adding supplimental light with LEDs may be difficult due to the distribution of energy, so careful placement must be taken to ensure problems do not arise from factors such as photodamage from too much light. It may be better to use the 1000w on its own, depending on how difficult it would be to integrate other lights with it. May requires some trial and error.
Yea I'm having a tough time aswell! I understand par and PPF but when I look at specs of a light idk how to make any sense of it!
Hey @drphoton I was looking at these lights and I was hoping you could give me a hand. They are cobs and I know you said they aren't as efficient but they do have alot of test reports I just don't know if they are good or bad!
They have 3 tests for different drivers I'm looking at the 2.4a driver tests https://chilledgrowlights.com/independent-lab-reports/lab-test-report-cree-xlamp-cxb3590-3500k-cd-bin
it's $340 for 3 of these in a fixture and that's good for 2x2 grow area!
Its a toss up, without true radiometric data its hard to difinitely say. Onr can only make a educated guess. There are measurements of these exact chips, but they are with different cooling systems and short operating times which makes it difficult to asses.
The heavy duty heatsink on the optic XL allows for higher efficiency, as heat is directly related to a diodes output efficiency. It also increases the lifespan of the fixture as COBs are notoriously known for breaking down much earlier compared to fixtures that use small surface mount diodes. They also use optics which helps lower optical losses.
The rapid LED could probably be as good. But i would choose the optic XL myself. Though you may want to look at MIGRO lights as well.
Yea and honestly if you have 3 lights and 3 drivers that's 3x the chance of something malfunctioning or breaking. Plus 3 side by side with probably not as good heat sinks would degrade them much faster! So I have my new top light (for now) will definitely check out migrow!
I'm gonna go back and look at your light article again I really didn't want to get a Cali light works cause I was scared of all the features. But I'm alot more experienced now it's just price that's the issue at this point!
Thanks so much your a bro ?
@drphoton i wanted to ask you about your input with using uv lighting for in my 5x5 grow tent.. running 1000watt hps an i want to get the flower power uv florescent tube lighting for both sides of my hid light, an have them run 10 15 mins an hour during flower.. I've just been looking into it an seems i can improve my thc count 15% to 30% more! Anyways would love your input on the subject uv lighting in flower ( uv a,uv b)
I have 2 Secret Jardin 25w 6500K lights for my seedlings.
I am building a dedicated rigg for my babies, and its big enough that i could probably run them for 4-6 weeks on this spot.
For me that`s beneficial considering i want to have a Flower room running 10weeks constant, and a paralell Veg room(by default also running 10 weeks). -This seedling rigg would add 4-6weeks on top of that Veg time, increasing size.
In bloom and Veg i run Cool Diamond`s 5500K: http://liltomatoconcepts.com/products.html
My question(s) is; how long is it optimal to run plants under my 6500K seedling lights? and IF i upgraded the lighting rigg with a Bloom (red) light would that be good (and when should i turn on the red light?)
If not, would a white spectrum 5500k be any better?
-red light seedlings: https://www.hydrohobby.co.uk/secret-jardin-led-bloom-26w.html
white light seedlings: https://www.mikrogartneriet.no/products/plantled-pro-5500k
My LilTomato lights 5500K i run in both Flower and Veg, are only 147w. Mounted max height, it gives my seedlings around 170PAR. -Could i simply just use this for my seedling rigg?
Thanx Dr Photon!
Heya knut, glad to meet you.
First i want to go over the growing system you are intending on using. Which from our private conversation is a perpetual system. Using a single flowering tent system. Where your seedlings are in a 2x2, vegging in a 2x4 and flowering in a 4x6.
Now when doing a perpetual. The flowering tent dictates what all the other tents should be. For example. A 4x4 (16 Square Feeet) flowering tent will require at least a 2x2 (4 square feet) vegging room. And a 5x5 (25 SF) flowering tent will ideally need at least 2.5x2.5 ( 6 SF) vegging tent. This is so that the vegging plants have enough space to grow so that when they are ready they are of the right size to satisfy the flowering tent.
What you have chosen is a good, with the vegging tent at 8 SF for a 24 SF flowering tent, you have more than enough room to satisfy most variables.
Lighting for your 2x2 (4 SF):
Using 2x24w @ 1.5umol per watt is 80 PPF (photon flux) for your seedling tent, which will give you 215 PPFD averaged. Which should be fine. There may need to be some experimenting with height in order to find the right intensity.
Lighting for your 4x6 (24 SF):
Using 6x147w @ 1.7umol per watt is 1500 PPF (photon flux) for your flowering tent, which will give you 645umol PPFD averaged. Which is perfect.
Lighting for your 2x4 (8 SF):
Using 2x147w @ 1.7umol per watt is 500 PPF for your vegging tent, which will give you 672umol PPFD averaged. Which is also perfect.
Plant Density And Veg Times:
The next area of focus is the plant density you will be using, which will dictate how long you will need to veg for. The more plants you have, the shorter the veg. It also changes when you need to initiate your seedlings. It can also affect what the most suitable lighting system will be for your vegging tent, but since you already have your lighting there is no need to look into that.
With a single flowering perpetual system. You have 8-10 weeks for getting the next batch of plants ready to replace the flowering plants. And as previously said, the number of plants or plant density you choose, will determine how long you will need to veg for and so when you need to start.
With your intended 8 plants, using our coco propagation and growing methods, it will only take about 4-5 weeks from seed to fill the 2x4. But how well you execute your grow will likely vary your results, so you will have to experiment when its best. Vegging for 10 weeks will likely produce plants that are way too big, which by the time they go into flower. Will be over sized. When you start your first batch you will be able to asses how long the first stage of growing will take and so when you will need to start the next batch by the time the flower plants need replacing. Over time as you develop things, your timing can change to reflect your improvements.
Saying that, you may want to consider using your vegging tent to start your seedlings also. This allows you to maximize the use of the available space due to your short veg times. It may be possible to use one of those cool diamond lights, with the right height. And then use the other as they grow more.
As far as light choices for seedlings or any grow light for that matter. Choose a neutral light spectrum. Research on plant lighting has shown that light quantity is more important than light quality when dealing with broad spectrum light sources. We only need a little blue to encourage healthy plant morphology. A little more blue during early development can be beneficial however to prevent excessive elongation, which is always good.
Just as a frame of reference, this is my system using 9 plants.
I have a 2x2 for my mother plant and a 2.5x2.5 for cloning and vegging. With a 4x4 for flowering. When my flowering plants have 4 weeks left i start the clones. Which takes 14 days to complete and transplant into their main vegging pots. Which another 14 days are spent under main vegetation lights. By the time the flower plants are finished, they are ready to replace them.
If you have any further questions, do not hesitate to ask. 🙂
Hey @drphoton do MH bulbs help dense up bud? Seen couple pages about it and was curious. Like I said in previous post I’m going to be running 4 HPS and 1 MH bulb (in the dead center) rest of this grow. People are saying to swap to all MH weeks 5-7 or what not to help dense up bud then go back to my 4 hps. Curious if any truth to that.
I wasn't sure if you would be interested in a few pics of my current grow, and how i have noticed the difference in bud building speed and size between a 315w c.m.h. lamp and on the other side, a 400 w H.P.S.
I have certainly seen the faster development with the two on the left under the cmh, and one on right under the hps. If you would like better pics please let me know.