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.
According to PlantMaid website,
| LUX | |
| Low Light Plants | 500-2500 |
| Medium Light Plants | 2500-10,000 |
| Bright Light Plants | 10,000-20,000 |
| Very Bright Light Plants | 20,000-50,00 |
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
Kitchen
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.
| 9am | 12pm | 3pm | 6pm | Average LUX | |
| Near Window | 75 | 232 | 292 | 258 | 214 |
| In Corner | Less than 10 | Less than 10 | 100 | 20 | 33 |
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.
Pantry
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.
| 9am | 12pm | 3pm | 6pm | Average Lux | |
| Aerogarden On | 294 | 315 | 243 | 148 | 250 |
| Aerogarden Off | 275 | 315 | 172 | 73 | 209 |
Laundry
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.
| 9am | 12pm | 3pm | 6pm | Average LUX | |
| Laundry | 150 | 235 | 173 | 109 | 167 |
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.
Where To From Here?
Beginners Guide To Hydroponic Lighting has a list of all our posts on lighting, written to help a beginner learn the basics and get started right through to more advanced topics.
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.