I think I’m just going to go the lux meter route for now. I’m still looking for a par meter I just can’t justify spending that on my first indoor grow. I really appreciate your comments and experience. 1 question though. I multiply the lux by .015 and that will give me par? Is that for full spectrum lights.I only ask because after doing some research I came to the conclusion it depends on your spectrum of lights being used. I can be 100% wrong. Just trying to figure it all out before germination. Thanks again
The lux meter is money well spent. I love the Apogee but if you can get 80% (or more) of the job done for 4% of the price (35/500) that's not even a decision.
The 0.015 factor is, pardon the pun,
spot on for the Vipar Spectra XS-1500 and the Chilled Growcraft X2 veg (a blue-heavy veg light). The spectrum for the XS-1500 is
here while the Chilled veg light is
here. All of the lights in the XS series have the same spectrum but the Chilled is very different. Despite that, the factor of 0.015 is very accurate. In contrast, the factor for the Chilled "full cycle" light (flower), is 0.016. In the real world, that's a tiny difference - at 0.015, 60k lux = 900µmols whereas at 0.016, 60k lux is 960µmols. That 60 unit difference (at very high light levels) is
just a bit above the calibrated accuracy of an Apogee (5%±).
Re. the specific spectrum - red photons carry more energy than blue and that's reflected (!) in the McCree curve so, yes, spectrum does make a difference. The question is how much of a difference and, second, what's the impact of the difference.
To my way of thinking, it's "measurable but insignificant". One reason is that we're trying to get to get to a
starting point in terms of setting out light levels. If you're a bit below the light saturation point for the current grow, you can always bump the PPFD. On the other hand, if you're seeing light avoidance behavior or other symptoms of too much light, shut out the lights 30 minutes early (assuming you're not growing photoperiods in flower ), drop the input wattage, or raise the light a bit (ATM, 1" of increased hang height drops PPFD by 50±µmols - that's just an example, mind you).
The other issue is that there are so many other variables that the difference in spectrum comes out in the wash.
Last point - Bugbee, perhaps in his video about light quality but I'd bet it's also in his "myths" video, emphasizes that the key issue for yield is how much light rather than which spectrum. The spectrum does matter - blue light tends to product plants that are shorter and have more foliage - but the point that he drives home is to get as much light as possible, up to the light saturation point.
Just to muddy the waters, Bugbee documents, but not in his "myths" video, the negative impact of blue light on yield but that's a discussion for a different posting (for ranges of blue photons up to the 20% amount which was the highest they test, an increase in percentage of blue light above 4% blue causes a 1% decrease in yield). That's one of the advantages to using a veg light and then switching to a flower light.
