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I'm trying to provide my houseplants with as much natural light as possible inside my 2nd floor apartment.

I have 2 large bay windows that face north, and can put my plants directly by the window/on the sill. Here they're very close to the window but almost never get direct sunlight, due to facing north.

I could instead put plants in rooms with a large east or west facing window, where they'd have access to more direct light depending on the time of day, but in each case the plants would need to be significantly farther away from the window itself (6-9ft).

Does anyone know which would offer more/better light to my plants? I'm sure there are other factors to consider (my latitude, size of window, perhaps even paint color/reflective surfaces in room) but I'm curious if there's a more general principle/formula at play, with proximity to window trumping light direction or the other way around.

Would an exposure/light meter help me figure this out?

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Having given Kevinsky a vote, because he's spot on, I want to add something. Do it the other way around, that is, consider the plant first. What plant is it, and what are its requirements in terms of warmth, humidity and light, then work out where's the best spot for it.

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The intensity of light drops off by the square of the distance. To compare a north exposure to an east or west exposure is challenging as it also depends on adjacent buildings and trees.

More importantly it depends on the plant. Where I live a Norfolk Island Pine is better off with indirect sunlight than right up against the window. A hoya or palm will take as much light as your exposure can deliver.

A light meter might help you decide but the type of plants and availability of artificial lights are just as important.

Edit: @OrganicLawnDIY is quite correct when they point out the intensity drops by the square of the distance from the source, not the window. However, I agree with Bamboo that the type of plant is just as important as the location. High light plants need to be close to a window, lower light plants can be farther away. The presence of blinds or sheers on windows also has a big effect on the intensity as well.

  • The distance measurements are incorrect. The source of the light is not the window. It's either the sun, or some other surface the sun is reflecting off of (sky, clouds, nearby structures). The drop in light intensity will not be as dramatic as you suggest, especially for direct light, because six feet difference is pretty insignificant compared to the distance of the sky or sun. – OrganicLawnDIY Sep 23 '13 at 13:14
  • @OrganicLawnDIY For direct light you're right- but for indirect you can treat the window more as a light source, since it is a diffuse light, and the light drops more dramatically. But of course there are a lot of factors which make it hard to give an exact rule... – Meep Jan 8 '14 at 19:21
  • @Meep. The window is still not the source of light. If it's not direct light from the sun then it's coming from another source like reflected off a building or clouds or whatever. But the window is not the source. – OrganicLawnDIY Jan 8 '14 at 21:48

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