Basil experiment: 440nm blue LED grow light

Growing Basil under 450nm LED

Summary:

Grew basil under a 50W LED at 450nm, at a distance of about 15 cm.  Growth was markedly inferior to plants grown on a window ledge in the September BC sun.

Problem:

Apparently blue wavelengths are optimal for promoting leafy growth, centered at around 430 nm.

Apparatus:

A bit of searching on Aliexpress turned up this 50W LED and matching driver at 450nm.

• LED - U$4.50
• Driver - U$6.50

It came without instructions, but it wasn't hard to figure out the polarity of the terminals.

The driver is rated for 30-34V, but only made about 28V.  It was still insanely bright, but got hot enough to melt the solder off after about 2 minutes.  Obviously it needed a heat sink.  That got me thinking about how to safely assemble the whole thing.

A 4.5" device box is just the thing to contain the driver.  It's fireproof, and it's already got 1/2" knockouts.

The driver didn't have mounting holes for standoffs, and this was a quick-and-dirty experiment, so I just made some clips out of strapping and screwed it onto a scrap of plywood.    I needed a buck power supply to generate 12V for the heat sink fan, but fortunately there was still enough room on the plywood.

Light intensity wasn't very high relative to sunlight, so I put the LED about 10cm above the basil.  The basil seemed to be browning a little after a week, possibly from excess IR, so I raised it 5cm.

Experiment:

I ran the LED on a lamp timer for 14 hours per day, for two weeks, on a tray of four recently propagated basil plants, watered with capillary ceramic watering spikes.

My control was two more cuttings from the same batch, placed on a south-facing kitchen window ledge, getting most of the day's late-september sun.

Results:

I didn't do any rigorous measurement, and one of the LED plants died.

The control basil had almost twice as much growth as the LED basil.

Conclusion:

The basil mostly didn't die, but wasn't very happy under the monochromatic light.

I should try another experiment in deep winter, doing actual growth measurements, and comparing against both the (very poor) BC winter sunlight, and a full-spectrum T5 grow light.