Grow light testing

[ShadyStump]

Let's get an idea of vocabulary before getting more confused.

Lux is a measurement of how bright the light is.
Kelvin is the color temperature of the light; higher numbers means cooler colors (blues and violets) and lower is warmer light colors (red, orange, yellow). A full spectrum light that tries to imitate sunlight is usually around 6000-ish kelvin.
PPFD/PAR is a loose rating of how much light that can be absorbed by a plant is being pumped out. This can be subjective as different plants have different needs, but it's very useful as an at-a-glance number to judge a light by. There are some nuances to be aware of when judging by PAR/PPFD, mostly that the standards for testing are not yet universal. One box may give you the average PAR over an area, but another will only tell you the max PAR measured in that one sweet spot. There's more, but not trying to overdo it in one post.

 

[ShadyStump]

Not true. You can get a LED panel for less than 100 USD.

There certainly are, and there are certainly good ones; but there also some really bad ones, and some that do great but only for a week.
To avoid getting into product testing and listing every light panel on the US market under $100, let's just go with rul of don't do that, at least until you know what your doing with lights.

 

[nurvbonsai]

Let's get an idea of vocabulary before getting more confused.

Lux is a measurement of how bright the light is.
Kelvin is the color temperature of the light; higher numbers means cooler colors (blues and violets) and lower is warmer light colors (red, orange, yellow). A full spectrum light that tries to imitate sunlight is usually around 6000-ish kelvin.
PPFD/PAR is a loose rating of how much light that can be absorbed by a plant is being pumped out. This can be subjective as different plants have different needs, but it's very useful as an at-a-glance number to judge a light by. There are some nuances to be aware of when judging by PAR/PPFD, mostly that the standards for testing are not yet universal. One box may give you the average PAR over an area, but another will only tell you the max PAR measured in that one sweet spot. There's more, but not trying to overdo it in one post.

I hear you. I went to film school so it’s not totally lost on me, but I also studied screenwriting instead of cinematography. Thank you.

 

[Glaucus]

PPFD is not subjective. It is the number of photons per second per area within a certain wavelength range. You can have a debate about which range this should be. But what is basically universally used is that it is all photons between 400 and 700 nanometers in photon wavelength. It may be that certain plants are better at using photons for photosynthesis that are 390 nm or 710nm. But this is the general term used.

 

[Paradox]

As an aquatic scientist with experience in seagrasses and measuring light in the ocean, in addition to keeping coral tanks and freshwater planted tanks, even I find all of the terms confusing to keep straight.

When I needed to get lights for my tropical trees (Ficus and BRT) for winter, I went with a K value close to what was suggested for freshwater aquarium plants and I looked for "Daylight bulbs" so they simulated daylight because I really dislike the pink lights. Then you have to consider wattage. Do the lights put out enough light to keep your plants happy for months.

I went with 6500K florescent lights (LEDS weren't yet there for the home consumer unless you wanted to pay lots of money).
Daylight spectrum
32 watt tubes.

I have 6 tubes over one table and 3 over another table. I think the plants under the 6 tubes do better than the ones under the 3 (more light), but these set ups have served me well for years. When I run out of the fluorescent tubes, I am going to replace them with LED tubes of equivalent light output to save energy costs and so the lights wont run as warm as the fluorescent tubes.

 

[ShadyStump]

PPFD is not subjective. It is the number of photons per second per area within a certain wavelength range. You can have a debate about which range this should be. But what is basically universally used is that it is all photons between 400 and 700 nanometers in photon wavelength. It may be that certain plants are better at using photons for photosynthesis that are 390 nm or 710nm. But this is the general term used.

Exactly.
PAR/PPFD is a measurement of all photons in that range.
Not necessarily the range a particular plant prefers, nor does the rating infer that particular grow light includes ALL wavelengths in that 400-700nm range. I've seen PAR rated green bulbs, but I wouldn't use just that for the whole winter.

I was just trying to make the point that you can't go just by the number and think you'll be fine. PAR/PPFD is very helpful, but you need to know exactly what it means and what to look for.

 

[Glaucus]

I still disagree. You can decide to not even look at the numbers, and still be fine. But if you want, you can look at the numbers. And all plants basically use the same light. Plants also use green light. So of course green bulbs would have a PAR value. They may not be monochromatic and actually be full spectrum. Or they may be green LED bulbs. Green is around 550nm so of course it is in the 400 to 700 range. You could have a curve for the relative quantum efficiency of all the photosynthetically active radiation. Which would give you a yield photon flux. And those curves can indeed be slightly different for different plants. But it basically doesn't matter if all you want to do is grow plants with an LED.