Grow 3, Day 6

Arise, my pretties! Also, more nerding about lights.

· 3 min read
Grow 3, Day 6


Diaz is still a touch wonky looking, but appears to be growing fine now. At least out of this frustrating batch of seeds, I'm likely to get one successful plant. She's gaining height quickly! Here she is in the solo cup, for scale.

Diaz, day 3 (day 6 overall) in her solo cup

Linetti is still unhatched (~6 days now) in a fresh paper towel and I'm waiting to see if Jeffords, who I started yesterday, has greater success. If only one more opens up, I'll be happy as I was planning to grow two of this cultivar. If neither opens up, then I'll plant more autoflowers so I don't have a bunch of photoperiod plants growing out of phase with each other.

Santiago is thriving still. Her leaves keep coming (...and they won't stop coming; fed her some nutes and she hit the ground runnin'...):

Santiago, day 6

I'm fascinated to see how she grows and how her ruderalis (autoflower) lineage expresses itself.


I've been measuring and mathing hard this past couple days trying to figure out the best lighting setup for coverage with my 3 lamps without overwhelming the plants with far more light than they can take. Fortunately, my big lamp, the Mars Hydro TSW-2000, is the newer edition with a dimmer, allowing me to lower its power level to compensate for the other two lamps. At around 55%, it seems to output at roughly the same brightness as each of the narrower SP-150 lamps. At around 50% I get about the same Lux reading at 36 inches, 24 inches, and 12 inches as everywhere else in the tent. This wasn't the case at shorter distances to the canopy during the flowering stage with the single lamp.

The lamps are not perfectly identical in spectrum, but close enough that using Lux to compare to each other is probably reasonable.

A view into the tent with lamp brightness balanced out. Pay no mind to Peralta's empty solo cup - it'll be repurposed if/when new seeds germinate.

As far as converting Lux from my phone's sensor to PPFD, using the TSW-2000's PPFD maps from the factory, I've narrowed down a coefficient (raised to height as its exponent) that produces results in my tent with a minimal offset from the factory measures:

Table of PPFD and Lux measurements and conversions. Blue values are derived from other measures. This is with each lamp isolated at full brightness.

The greatest degree of drift is seen in the SP-150 measurement at 18 inches as compared to the factory PPFD map. I attribute this to a different sized tent in their measures along with my SP-150 lamps being nearer to the walls of the tent than the centre (more intensely reflected light).

I also took measures in Lux with all lamps on at full brightness in the centre of the tent. The results line up with my expectations, though clearly it's far too bright in there for cannabis plants (at least without supplementation of CO2) with all lamps at full.

Measurements in tent with all lights on at full power. Far too bright for cannabis without CO2 at 18 inches and under.

Fortunately, when the TSW-2000 is turned down, the numbers fall into far more reasonable ranges. I haven't gone back in with the tape measure to measure the new levels yet, but I'm very confident based on measurements at the plants. Now I'm just monitoring temperature to ensure the tent doesn't get too hot. I haven't turned on the exhaust fan yet as I wanted to maintain the humidity levels.

As the plants are still tiny, there's not necessarily any reason to run all the lamps, but I want to make sure I have the right settings measured and dialed in before I get to a stage where they are needed.

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