Supplemental light: PPFD vs Foot Candles

[rockyfarm]

After digging around in the lux/ppfd/dli information online, I've decided to modernize my growing conditions with a new PAR meter. I'm a little unclear on whether this meter will process all energy in the 400-700 band, or will weight it, favoring those wavelengths best for plants. At present, it sounds like we assume any energy within that band gets lumped into a single number.

I like the idea of the 'dli', since it explains how we can grow plants under lights with (relatively) low intensities by increasing daylength (and keeping the same exposure all day). This makes me wonder whether the low/moderate ppfd levels would produce darker green foliage than we normally would like to see, but the extra chlorophyll would actually be better adapted to process the low light more effectively than the light green foliage resulting from regular intense light. Any thoughts?

[Ray]

A “perfect” PAR meter would give you the photon flux of 100% of the photons between-, and including 400 to 700 nm wavelengths. In reality, the sensitivity may drop off a bit at the ends of that range and may even count a small amount barely outside of it, and more accurate readings usually come with a higher purchase price.

I agree that DLI is a good figure to work with, but that does not mean that “X” moles of photons acquired in 8 hours is the same as “X” moles acquired in 16. The chemical reactions involved with capturing those photons take time, different plants have different metabolic rates, and some chemical reactions going on within the plant are done when it is light and others when it is dark.

Certainly, plants have some flexibility about those, but it takes them a while to change from one to another, and if the change is too extreme, it may not survive.

[rockyfarm]

Thanks for your reply. With regard to the PAR meter; the output number might look the same for a source heavy with green light as for one uniformly distributed from blue through red, or even with red and blue peaks. Would our plants really benefit the same from each of these three?

Your comment regarding chemical processing sounds very reasonable; one might think the longer daylength at lower light levels would give more time for efficient nutrient processing and metabolizing. Too bad we can't ask the plants for their preferences.

[estación seca]

For many years people judged light by looking at their plants, and how they grew. This is still the best method. Light meters are helpful guides but the grower still has to decide whether the plant is growing optimally.

[MateoinLosAngeles]

Originally Posted by estación seca

For many years people judged light by looking at their plants, and how they grew. This is still the best method. Light meters are helpful guides but the grower still has to decide whether the plant is growing optimally.

Fair enough but it doesn't hurt to use technology to get a good head start. The less time spent re-arranging lights, moving shelves up and down, or hanging curtains and cloth, the more we can spend watering our plants, staring at our plants, or my favorite... buying new plants!

PS. I've found the Photone app for iPhone to be extremely helpful. Many people have compared it with Apogee meters, and the consensus is the app will be within 20% of the Apogee reader, which is not bad, and as long as it's not over the recommended limits it might be really helpful as a guide.

Another thing I've been playing with is getting 1 ft LED bars that can be individually turned off. Placed strategically, you can get even light throughout your shelves and still turn off a few lights if you overdo it without having to readjust the entire setup. Also... I really recommend having light concentrated towards the front of the shelves... having spikes approaching 3ft long it becomes really helpful to direct them "out" so the buds don't burn under the hot LEDs. You can have LEDs of a higher intensity placed on the front and only turn them on when the spikes initiate...

[rockyfarm]

Of course the plants are the ultimate measure! But they are slow to show symptoms of poor growing conditions, unless the environment is really severely 'off' and damage has been done. I grow under lights, previously fluorescent fixtures, now pairs of cool white and warm white bulbs, and finally have noticed that many plants in my collection seem not as green as I remember; they're yellow/green, and the Brassavola hybrid leaves have lots of red pigment. I used a conventional light meter to check things and the numbers looked reasonable, so I thought maybe I was keeping the plant room too hot? A quick check using the Photone app with my cell phone indicates that PAR is a lot too high for many of the plants. The plants are moved annually from a summer grow room in Maine to a winter room in North Carolina, so I'm buying a PAR meter to try to correct the light levels in both places.

Things were simpler when I just had a greenhouse in Florida, until a freeze took out most of that collection. Still learning after 58 years of growing orchids, sometimes it's back to fundamentals.

[Jmoney]

also look up High Desert Orchids. I know Kelly no longer sells commercially but I found her articles extremely informative and I bit the bullet and got a quantum PPAR meter. Playing with it under various natural light sources was "illuminating" (groan). I used it to calibrate my transition to LED. (I still overdosed the plants, but mostly because they came from winter in the home in the NE on a crowded windowsill).

[Clawhammer]

I bought a par meter when setting up my basement grow room. Since then I have changed everything and not used the light meter once. It is a good training tool, but ultimately it only tells you about one variable, and not that accurately as leaves at the bottom of the plant get a different par than ones at the top. Some are in a shadier spot because they are short, while others grow into the lights and get burnt. The meter doesn't tell you about photoperiod or how the light interplays with temperature at certain times of the year. So don't spend too much money because once you get familiar with your lights and the effects of light on your plants, you will probably not use it.

One thing it can be good for long term is understanding if your lights are wearing out.

[Jmoney]

I still use my PPAR meter regularly when moving plants around to find the optimal area, and also when I add new plants. I agree it's not the "gospel" but I find it continues to be a useful tool and worth my investment. and of course the bottom leaves (and leaves shaded by other plants) will not receive the same intensity as the canopy.

I believe there are other ways aside from spending $400 on approximating this data even from smartphones.

[rockyfarm]

I like the idea of integrating the PPFD value(s) over time (DLI) so I can manage daylength, under lights for optimum plant 'satisfaction'. I'm interested in cutting back the light intensities a bit to reduce their heating effect on my grow rooms.