Supplement grow light for window gardening

A project log for Collection of Misc Small Project

Here is a collection of some of my small hacks. They take minutes to an evening and even then procrastination gets the better of me.

K.C. LeeK.C. Lee 02/19/2018 at 23:350 Comments

The green onions tends to bent very easily in my Urban Window Garden.  There is very little amount of direct sunlight in Feb. in Canada.  I'll need to supplement the light intensity and increase the day:night ratio to 1:1.

From Light Reactions at  There are lots of the biology on this page.  

Plants use a mixture of chlorophyll pigments and Antenna Pigment Complex to make use of a wide spectrum of light.  The main absorption peaks are around Blue (450nm) and Red.

Spectrum of sunlight vs time of day (source).

One easy and good source of light turns out to be white LED.  The phosphor coating that absorbs blue light and converting into yellow.  The various color temperature are achieved from balance of blue to phosphor converted light.

Of particular interest is the Blue light component is very close to the blue peaks in plants.  The 6500K LED has higher proportion of blue light output.

Here is my setup:

I use two sections of 50cm LED strips suspending from the two ends of the window frame.  I use solid wire at the solder pads on the strip to provide mechanical support, electrical connections and maintain separation between the two strips.

The left side is a couple pieces of wood from a mandarin orange case.  The blue rubber bands provides fiction fit and tension to the strip.  Most of the forces is applied to a third solid wire running down the strip.  The block can be moved for height adjustments.

On the right side, I made a hook out of transformer core and is attached to the window frame.

An AC outlet timer controls the light.  My tomato plant starts to open up its leaves around 5am and closes at 5:30pm, so that's what I set the timer to.  (Daylight for Ottawa in mid Feb: 7:00am to 5:30pm.)

With the light supplement, the branches green onion now seems a bit stronger. 

3 weeks later...    The green onions leaves are now stronger.  I have decided to run the LED strips at an angle to accommodate the drastically different growth rates a few days ago.  I might have to give away the tomato plant soon as it can grow to 6 feet tall outdoors by fall.  The basil have finally decided to grow due to the warmer soil temperature from the morning sun. 

The leaves for the parsley (middle) are parallel to the LED strip when it is the stronger light source.  Mean while the basil plant (right) is tilted towards the left.  It might be is trying to get the right side closer to the light strip.