After researching a bit, and probably jumping into the water too fast when it comes to buying products like grow lights, I have purchased some seeds to grow in my Krakty hydroponic room setup.
Buying seeds was a specific hassle in Kuwait; the very few and limited stores that sold seeds only sold very common varieties. Think Beefsteak tomatoes; the probably most common tomato you can find at any supermarket. Since such tomatoes are so easy to buy, I want to grow something more unique.
In fact, we even found a nursery selling seeds with the giant warning label on the back: “Warning. Treated with poison. Do not consume or grow food products from these.” What?!
In the post Do I Need Grow Lights I measured the amount of light in each of my grow rooms, hoping to figure out which room would produce the best plant growth. At the time I was hoping to not have to invest in a grow light; man was I wrong!
A Short Warning
LUX, or lumens, to determine plant growth is widely inaccurate due to the different types of lights and the wavelengths light types each produce. Plants need certain wavelengths, or colors, to grow. No matter how bright your lights are if they are missing those wavelengths then then the plants will just not grow.
This post will not consider the wavelength or colors of lights. I’m trying to keep it as simple as possible so that anyone can follow along, even without fancy gadgets like quantum meters which can easily cost US$500. Future posts will explain wavelengths in detail. Beginners Guide To Hydroponic Lighting has a list of all the posts on how to measure and set up your lights.
You need the umol’s value or the umol/s/m2: in essence umols are how bright your light is. This value is also known as “photosynthetic photon flux” or PPF. Note that PPFD is a different value, taking into account the distance from the light.
Too low of a light strength on your plants may lead them to not growing, and too high may burn or kill them.
How To Calculate Bright Your Light Is
Most people don’t have fancy tools to measure the amount of light in their homes, such as a PAR meter or a quantum meter. Thankfully, you can get free apps on your phone that measure lumens easily.
You can use the Plantekno website to convert LUX to umol/s/m2. Note: many grow lights will tell you the PPF or umol/s/m2.
Natural sunlight has a PAR value of 900-2000μMol/m2/s when directly overhead, varying with location and season. For a grow light to be effective, it will have PAR values of 500-1500 μMol/m2/s.
In comparison, I measured my kitchen window light at 250LUX or 4.6umol/s/m2. No wonder my plants kept dying! As you’ll see below, its way below the minimum light requirements for lettuce to grow.
But how bright should my light be?
Be aware that not all aspects of how much light plants need are fully researched yet : Lefsrud at McGill University has extended upon NASA research and one thing he noted was common incorrect assumptions. For example, many people consider lettuce to a shade loving plant and tomatoes to enjoy full sun. However when shone with 5000 umol’s, the tomatoes suffered whilst the lettuce showed no signs at all! The exact opposite of what was expected.
Research Gate website had several listed studies that mentioned the number of umol’s used for ideal plant growth:
Minimum umol’s Required
According to the company Valoya the amount of umol’s a plant needs will vary depending upon its growth stage: seedling, vegetative, flowering/fruiting. They claim that lettuce needs approximately 80 umols during seedling, 150 for vegetative stage and 200 when it begins to flower.
I found a really great article from the Department of Horticulture and Crop Science: this PDF covers a huge variety of plants, and the recommended lighting and hours lit for each of the growth stages, and what level nutrient solution is ideal.
Here is a small sampling of some common plants and their needed light intensity (taken from above PDF link):
# Light Hours
Light Intensity (umols)
# Light Hours
Light Intensity (umols)
# Light Hours
Light Intensity (umols)
Where To From Here?
Notice how I mentioned the number of light hours needed for plants in the tables above? Different plants need different lengths of light exposure. You can’t just leave your grow light on 24/7! The next post in this series is How Long Should My Hydroponic Lights Be On? It explores Daily Light Integral or DLI, the measurement that takes into account growth light strength x time its on for optimal growth.
Do I Need Grow Lights? is the previous step in this series. Not everyone has a PAR meter or Quantum meter; they can be expensive. So how else can you measure the light your room gets? Whilst not very accurate, this can give you an idea of how bright your rooms are; helpful in finding out if you need to invest in a grow lamp!
How Long Should My Grow Lights Be On For Hydroponics? is the next step in this series. You know how bright your light should be, but how long should it shine? Plants need time to sleep and rest too, just like you. This post explores how to determine how many hours of light your plant needs (it can vary a little depending upon how bright your light is).
On the 17th July 2019 I planted some Deer Tongue Lettuce into our Aerogarden Bounty. My goal was to use the Aerogarden as a seedling starter to then transplant the lettuce sprouts into mason jars to test the Kratky hydroponics methods. Instead of using the traditional Aerogarden pods, we used Jiffy 36mm peat pellets inside the old aerogarden plastic cups.
On the 21st I painted some old unused mason jars with simple black gesso (two coats) to block out any light. I used some old yoghurt containers that just happened to fit perfectly on the mason jar. Using scissors, I simply cut some holes in the bottom.
I transferred the Jiffy peat pellet into the yoghurt container, and then propped it up with clay pebbles. The pebbles help block out any extra light out from reaching the bottom of the yoghurt container and leaking in to the nutrient rich water, as well as to help provide stability to the peat plug. The nutrients we used were from General Hydroponics.
To test the growing factors in each of my primary growing rooms, I placed one lettuce in my kitchen, one in the laundry, and one in the pantry.
1 Week Update
So how has the little lettuce been faring this last week? Already there is significant differences between each plant!
The first thing of note is that they have all survived! I was quite worried at least one would die during transplant. They have all grown, some more than others. All the peat moss plugs are still damp, meaning that each plant is still getting somewhat equal amounts of nutrients.
The lettuce from the pantry has clearly grown the most. It’s over 2x the size! We purposely put this plant beside an active Aerogarden as we figured we could capture spilled light from the Aerogarden rather than purchase grow lamps, after all the lettuce tubs can fit on the same shelf. This definitely gave an unfair advantage to the other two plants, but also allowed us to test how the Kratky method would compare grow light vs no-grow light.
This plants leaves are long and thin. Comparing with the Aerogarden, those lettuce leaves are slightly shorter but much wider. I currently don’t know why lettuce leaves will be thin or thick at the same age.
Finally, I should note that only one small root has emerged from the holes in the yoghurt container. At the moment its “just” peaking out, so not a strong root yet. This is the only plant that has shown any sign of roots beyond the yoghurt container.
It also seems that now the plants are bigger, there seems to be three seeds that have successfully grown in this one plug.
Contrasted with the actual AeroGarden model which leaves are much wider at the same length.
Laundry & Kitchen
These two sprouts are very similar. The lettuce from the laundry seems to be ever so slightly longer. The leaves are also about the same width, despite the picture above making the lettuce from the kitchen appear thicker (camera angle).
The leaves on the lettuce from the laundry seem more droopy, whereas the kitchen leaves are pointing straight upwards more. I am currently unsure what could cause this; more research will be done and we shall see how they perform over the next few weeks.
Plants need light to grow, obviously. But what is the ideal amount of light? Honestly this question is quite debatable as growth is effected by the strength of light and how long the plants receive light.
I decided to test how much light each of my primary grow rooms are receiving; these are the rooms that I would like to ideally be growing herbs and vegetables indoors. I wanted to know if I could grow plants from the sunlight coming in, rather than buy a grow light. I measured the light amounts throughout the day, as the sun will shift and rooms that might get more light in the morning might receive very little in the afternoon and vice versa.
Lumens and Foot Candles
Warning in using this method
Measuring by lumens and foot candles are both considered widely inaccurate due to the different types of lights and the wavelengths light types each produce. Whilst we can see the light, plants need specific wavelengths to grow. Unfortunately most people don’t have fancy tools to measure the amount of light in their homes, such as a PAR meter or a quantum meter.
Even a rough idea of how much light your plants is getting is better than having no idea, so don’t get discouraged.
How To Measure
Thankfully, you can get a bunch of free apps on your phone that measure lumens easily and then with a bit of maths we can then convert the lumens value to the correct value, umol. I used an app on iOS called “Light Meter”. I did not buy the full version.
I like working in metric units – I just visualise meters easier than feet. Lumens are a metric unit, whereas foot candles are imperial. If you want to convert between the two:
1 foot-candle is equal to 10.76 lux, and this is derived from 1 lumen/square meter = 1 lumen/10.76 square feet. (One square meter = 10.76 square feet).
Minimum Lumens Needed
It was really hard to find this information, since everyone agrees that lumens are not an ideal way to measure light for plants. Furthermore, when most people talk about lights and plants, they will use the measrument unit umols/m2/s or PPF. The post How Bright Should My Hydroponics Light Be? goes much more into depth about what plants need what level of light.
None-the-less, this post is to help you know if you potentially need a grow light. So at a very quick glance at the tables below you should be able to tell if your plants may survive in their current lighting setup.
Even LumiGrowth website says that plants ideally need 3230-8610lumens/m2 in order to grow.
Obviously these values will all vary depending upon the size of the plant, its life stage (vegative vs fruiting) and the type of plant. Again, check out How Bright Should My Hydroponics Light Be? as this post has much more detail.
My Own Measurements
The following light measurements were taken in my kitchen. I have two locations where I tend to want to keep plants; in the back corner on counters that are rarely used, and underneath the window.
Less than 10
Less than 10
I was honestly surprised that the back corner of the kitchen got so little light. I knew that the kitchen could get quite dark, but the ambient light didn’t seem that dark during the day. This could explain why many of the plants I put in the back corner would keep dying as they were receiving so little light. I thought I just had the opposite of a green thumb…
I was surprised to see that the Kitchen Window (214) received more light than the Laundry (167) overall, as I thought that this area was darker since there is a building overhang. Given this information I may buy a shelf that I can install near the window.
The pantry receives the most natural light out of all my “grow rooms”. The room just seems to be ideally faced (at least in summer) to receive bright light throughout the entire day.
Its also in this room that we have our Aerogarden Bount models currently set up. I took light measurements with the Aerogarden lights both on and off, as the machines will regulate for their specific plants, but light will overflow to the rest of the room when running. The pantry has multiple shelves where plants can be placed, so I measured whilst standing in the centre of the room at equal distance between all shelves. This room does have a window, so one wall will certainly have much more light than others.
Unlike most people, we have an indoor laundry. We get too much dust in Kuwait to realistically hang our clothes outside; so we have a washing machine and fold out line installed in a “small” room. It’s a bit like a mud-room. The laundry will be our primary grow room, at least for larger plants such as tomatoes. Its not as highly accessed as other rooms, so the plants will go undisturbed. And the room tends to be slightly more humid than other rooms.
We already know that this is one of our darkest rooms. The window is very small and doesn’t seem to receive much natural light. We are planning to put a grow light in this room in a few days, but we are testing to see how it performs without.
What Did We Learn
After measuring the light intensity in all my ideal rooms, I have learnt that none of the rooms have enough light to grow any plants. The brightest area was 250 lux, and unfortunately low light plants will need at least 500 lux. So it seems that for me to grow any plants indoors I will need to invest in a couple of grow lights.
The post How Bright Should My Hydroponics Light Be? is the next step in this series. It explores how much light certain plants needs to grow. I also show you how to convert to the more common used light measurement value umols or PPF, which many grow lights use. Understanding these values, and how they get them, will help you make an informed purchase.