Should I stop watering my South African bulbs?

[Xephre]

Nope, I'm growing them indoors. 

[Arnold]

I originally had the lights on into the evening.   After talking to a couple of other growers I just have them on during daylight hours to augment the natural light.

Plants need a dark period to finish their metabolic cycle

[CG100]

I used to work for General Electric in light source (lamp) research and cannot recommend highly or strongly enough, that anyone using supplemental light, buy a cheap luxmeter - somewhere in the region of $20-35.

The human eye has an iris and what you think you see is not what is really happening because your iris corrects for light level. (for instance - most people can read a book at under 10 lux, bright UK sunlight is somewhat over 100,000 lux).

Insolation is also highly influenced by day-length - even the north of the UK has very long days in summer - something like 30% longer than any point in RSA.

Philips, being a Dutch company, not surprisingly specialise in horticultural lighting, and have done so for many years. They have loaded masses of information to the www, free to view, for instance -  20230124-philips-gridlighting-technical-specification-sheet.pdf

Despite what anyone's eyes may tell them, increasing light intensity when sunlight is the primary source, at anything but considerable cost, is essentially impossible. Extending day-length, which can be at very low irradiance to achieve any effect in the plants, is actually cheap and easy.

[Arnold]

CG100

I've read that you can use the light meter in a good camera to measure light source using a grey card.

Have you seen or heard of this?

Thanks,

[CG100]

CG100

I've read that you can use the light meter in a good camera to measure light source using a grey card.

Have you seen or heard of this?

Thanks,

That rings a bell from a looooonng time ago, but if anyone understands how they all work together, you will get comparable results. They may not be accurate in the true sense, but they will be comparable - if you get a reading of double, it will be double, but double what? And the what does not matter when you are just experimenting. If that makes sense?

The advantage of using a cheap luxmeter is that the sensor area, the whole meter, is small.

What neither, or at least certainly the cheap luxmeter, allows for is colour temperature (CCT). A cheap luxmeter will be calibrated to some arbitary solar spectrum (I would guess - if only I still had access to a photometer to calibrate one..................), although cameras frequently have the ability to select between "full sun" and "shade", or change other related parameters, which will affect the spectrum that it reacts to. All that said, correlating any human eye figures to how a plant "sees" things is another hassle entirely.

There are plant lux meters available, but they are worse than horribly expensive (unless you are a farmer growing 100's tonnes of tomatoes and want to be sure that your expenditure on supplemental light is money well spent). The meters are many $100's.

Lux/lumen are not an SI unit or anything equivalent. The ones that you see quoted 99.99% of the time are based on the average human eye sensitivity (there are even photopic and scotopic versions). The human eye sensitivity has not a great deal to do with how plants react to light. For anyone growing greenhouse crops for a living this can be extremely important across a lot of the world, but is whole can o' worms for the amateur.

[Arnold]

Thanks CG100

I think we know that my light levels here in the NE USA are low compared to the natural setting of my SA plants.

It's made a great deal of a difference adding a 8 foot strip of a LED fixture over the plant area  with some red diodes included.

It's worked so far.

[CG100]

Vegetative growth is stimulated most by light in the yellow-orange-red, which is why HPS/SON/Lucalox was the lighting used commercially until LEDs came along. Inter-nodal distance (how "leggy" a plant is), is controlled by blue light, and rather little is needed, although quite a bit more than is emitted by SON, which emits very little.

[Steve Marak]

I've read that you can use the light meter in a good camera to measure light source using a grey card.

Have you seen or heard of this?

I tested this, because I used to do a talk on artificial light for orchids and it's one of those questions that always comes up. I had a couple of pretty expensive DSLR cameras around, and thanks to a friend not all from the same maker, and I couldn't find any good correlation to either my lux/footcandle or much more expensive PAR light meters.

I didn't reach the level of scientific rigor required to definitively say there's not a way with some particular camera and lens and reflective surface and technique, but I tried a grey card and several types of white surfaces, at different angles from  the camera lens pointed as directly down at the measured surface as possible without casting shadows to a rather shallow angle, and with several different light sources and a couple of lenses. The meters have diffusers and can be pointed directly at the light sources, but pointing the cameras directly at the light sources gave wildly variable numbers depending on the exact angle, and was very much not recommended for at least one (e.g., the sun) so the cameras were always seeing reflected light.

A side note - one thing I tried that surprised me by working, and rather well, was an app for my phone to measure color temperature. I tested it against several LED sources of "known" color temperature, and in every case the phone app was close enough. It's handy for photography.

Steve