MAINTAINING YOUR PLANTS:
The intensity; it is so hard to judge the with your eye, as they are so good at adjusting. In the open, around equator, the intensity can reach 2000-2200 µE/M2/s (110-120 K Lux), but the plants don't use that much at all. I think most of our plants will grow nicely with 150-300 µE/M2/s. In winter, I can measure 1100 µE/M2/s outside the window in the sun, where the plants in my windowsill only receive 750 µE/M2/s in the direct sun, right behind the glass windows, and 13 µE/M2/s a meter inside the room, in the shadow.
Measuring light can be done in several ways. Common for them is: It is rather expensive. I use µE/M2/s (=KW/M2/gr), which is the number of photons that hit the surface. Other meters use Lux or Candela. The relation is a bit tricky, as Lux changes with the colour of the light. However, you can buy a Lux-meter for around €70, and that is a good tool.
The colour is another factor. Where the sun have
a a wide range, light-tubes, bulbs and LED light have a combination,
fooling us to think "white". The plants mainly use two specific ranges of
blue and red, and you can buy light-sources with these colours. But they are
more expensive, and personally, I hate that colour! Using the average
white might cost you a bit more electricity, but the tubes/LED is so
more inexpensive, and I can only measure small differences in growth.
The type of light source is important. If you live in an area with sufficient natural light, it is great, but some need to add artificial light. I have used all kinds of sodium-lamps, bulbs, tubes and recently; LED, which is SO great. You don't spend electricity on heat, everything become light. Further more, you can set the light right down on the plants, and save a lot that way.
How much light a specific plant need, is had to
At first, I thought i.e. cacti from Mexico would get the full
blast. But it turns out, the young plants are only found under the
bushes, not in the open.
During the winter, many of us have way too little natural light to have our plants grow. It might be necessary to force them into dormancy. That might solve another problem as well: Temperature.