Sorry but this is simply not true. You seem to be confused about the fundamental difference between the light meters being discussed here. PAR literally stands for photosynthetically active radiation, i.e. the area of the “light” (radiation) spectrum that IS used by plants to grow, or activate photosynthesis. No parts of the PAR spectrum (400-700nm) contain wavelengths that are “useless” to plants.
Now, for the “mostly” part: It’s true that some parts of the PAR bandwidth are used more efficiently by plants, mainly the deep blue (450nm) and deep red (660nm) bands, and it is true that a typical PAR meter does not distinguish between the very-efficient and least-efficient bands. But all bands are useful - you can grow with green light, just not as well. The McCree Curve is literally a graphic representation of the relative photosynthetic efficiency of those wavelengths - and none of them are even close to 0% efficient - in fact the much-maligned green band is only 15% less efficient than the red band.
And it is true that recent research has identified photosynthetically active wavelengths down to 280 nm and up to 800 nm. But not enough study has been done to confirm the degree of importance of these wavelengths to healthy plant growth and flower production. They remain curiosities in terms of utility and effect on plant growth, and fodder for growlight marketing pitches looking to sell the next new thing to gullible customers.
Those cheap probes measure only foot-candles/lux, i.e. lumens as discussed by the OP. And they do so extremely poorly and only below the intensity range needed for robust cannabis growth. A bad free phone app will do a better job than any garden store probe at measuring lumen intensity.
I may have been off about PAR but from all I’ve been reading over the years there are many frequencies in that range that are not helping grow pot and the curve in the pic you added just smooths out the dips.
I totally disagree tho that those cheap garden probes are of no use or worse than free phone apps that can’t even measure the output from my lamps at 4 ft away. They overload right away and could only give me a solid reading a foot away from my old T-12 bank of fluoro tubes. Went totally off scale under HIDs.
I just want to see the intensity at different spots so I know here I’m getting the most and least light and the cheapo probe does that just fine. I know it’s not telling me the quality of the light and I don’t really care to know that. I’m using good bulbs like Hortilux and SunMaster so I trust them to have good light for my plants.
Even a good PAR meter isn’t telling you things like the ratio between red and blue light and there’s no justification to spend a bunch of money on one for the average small home grower IMO. You’d need a very expensive spectra-graph or some such to know how much of what frequency your light put out and that data can usually be found at the manufacturers website. Plenty of other useful things a person can buy with that money to enhance their grow in a meaningful way.
If you’re a pro getting paid good money to set up grow rooms then A PAR meter will make you look more pro but even being able to test for intensity of light output is enough for most of that too.
@Labrat I’m sorry but you are not speaking from knowledge on this subject and need to go back to the beginning of the thread and take it in before you comment further. Light measurement is not a matter of opinion, it is science based upon established fact replicated and confirmed by serious researchers over time.
The PAR map IS the definitive graphic presentation of the accepted research since the 1970s on what parts of the light spectrum are used by plants. It doesn’t “smooth over the dips”, it accurately represents them. If you need to go to the research to confirm this, Google Dr. Bruce Bugby or Dr. Keith McCree.
Cheap garden probes and light meters used for photography are entirely unsuited for measuring light at the full sunlight-like levels needed for cannabis because those meters are designed for indoor houseplants and photography where light levels are typically 1/10th of outdoor full-sun intensities. Any discussion about using them is just a distraction from serious discussion about growroom light measurement.
Lux Light Meter Pro is a free IOS app that has the range for growroom intensities I’ve used before. Still limited to lux, not PAR, but reasonably responsive and accurate at the 20,000-50,000 lux range you need.
Edit: after a new search of the IOS apps available for light analysis, I came across Korona
Free IOS app available now, Android coming soon. Does PAR, PPFD, DLI and lux - everything you’d basically need. Their website has a blog with some fairly convincing testing of their app and others in actual grow lighting environments. I’m liking it a lot right now. Still not a true PAR meter as it uses a camera lens vs. a PAR sensor but so far looks like a great alternative for small growers. Peace -b420
sorry, oh cellphones, don’t use one. I build computers, for fun in my spare time. If it can’t be done on a computer, or a regular phone, I’m out. thanks for your comment and time.
