I often see and hear people saying "this plant needs light". What is light? Just sunlight(direct and indirect) or what else? My room doesn't get a bit of sunlight, direct or indirect, but there is light.
Can anyone help me with all this light requirement by plants?
EDIT:
Plant 1: Under indirect light?
Plant 2: Under direct or indirect light?
This is the actual confusion. Wouldn't it be weird to say that Plant 1 is under no light, Because there is light, and that's why we can see it, right?
With regard to plants, direct sunlight and daylight are two different things. Technically, all natural light is derived from the sun, but there are many plants which do not appreciate direct sunlight, preferring instead dappled sun, or partial shade, or indirect light with no direct sunlight at all.
Regarding houseplants, proximity to a window means more light, and there are differences in natural light requirements between different varieties of plant, even those described as not liking direct sunlight. An Aspidistra, for example, will be fine in very low light conditions, whereas many Dracaena varieties will do better closer to natural light.
If you're considering whether there are any plants you could grow in your room, there will be, but your choice may be more restricted if the ambient light is low, i.e., there's a tall building opposite and not far from your window, or a tree very close. Equally, a heat source like a radiator beneath your window will mean you can't put a plant very close or on the windowsill, but there will be something you can grow.
If you have no window, then you will need a growlight of some sort.
UPDATE:
I think your confusion is with terminology as much as anything - both plants in the image you've added are in indirect light, or shade conditions - the word 'direct' is usually applied to sunlight rather than just light. Plant 2 is in good light, plant 1 is in poor light, so plant 1 needs to be one that tolerates low light conditions.
Plants needs lights (with some exceptions) and this light is used as energy input of plants, which is then converted is some chemical molecules, so that the energy distributed in the rest of the plant (sugars and other molecules). Animals needs to eat, in order to get energy. Note: roots give nutrients but usually no energy (energetic nutrients) (again with some exceptions, some plant steal food from other plants using their roots).
In general all sources of light could help a plant to grow, but this light should be energetic. Our eyes could see also with very low light, and artificial light has very low energy compared to sun. So with artificial light, you need to provide a lot of energy, so using a lot of powerful lamps.
Then some type of lamps are better then other: incandescent (bulb) lamps uses the black body principe (so with heating), which is similar to sun surface, so incandescent lamps have similar frequency distribution of sun. (really they are not so hot, so not so "blue" like noon sun, but instead more reddish, like late afternoon sun light). Other technologies have different distribution of the frequency of light, so they could be less suited (but also not every plant want full sun-light), but because our eye is more sensible with the "green" part of light (also because it is the most strong frequency of visible light of sun), most of lamps have high emission in green frequencies (too much blue is not so good for eyes)
