is there a method to determine the light output of LED lights needed to achieve a reasonable ISO/shutter/aperture combination to take close-up (not necessarily macro) photos of indoor plants given a fixed distance from light source to subject.

  • Are you looking at using household LED bulbs, or lights designed for photography (or video)?
    – mattdm
    Nov 8 '19 at 18:43
  • @mattdm If its possible to get household type LEDs with enough output I'd prefer them so they could be used elsewhere. If not I'd use ones designed for photography Nov 8 '19 at 21:21
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    What is a "reasonable" ISO/shutter/aperture combination to you? One person's reasonable combination is another person's tedious setup.
    – scottbb
    Nov 8 '19 at 21:54
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    Is there a context for this? I mean, are you taking pictures for the purposes of selling them (people often want completely white backgrounds when selling items)? Or is it for documentary/cataloging purposes, such as botany collections, etc.? Or are you taking pictures of houseplants in their native environment (i.e., sitting on an end table against a dark wood-paneled wall in a house)? ;-)
    – scottbb
    Nov 8 '19 at 22:01
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    Household LED lighting is usually no good for photo setups. Horrible CRI issues, and if it is dimmable at all it dims in a way that causes artifacts, shifts color and is non-contigous... Nov 9 '19 at 12:12

If you use a directional light, and we make some assumptions, we can roughly calculate the shutter speed for the ISO and f stop in your comment.

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As a sanity check, here is the calculation for my test setup. It is a stop off, so some of the assumptions aren't correct. This is only a ballpark calculation anyway.

enter image description here

More comments on my test setup. A typical household interior has an EV of 5-7. With one 8W LED spotlight at 18 inches away, and a white reflector on the other side, I measured about EV 9 (based on my test exposure). You can get more powerful spotlights or you could use several. A distance of 18 inches is a little close, you probably want to be further away to get more even lighting. So, I am going to use EV 9 for the remainder of the calculations.

ISO   Aperture  Shutter
800   f8        1/60     With image stabilization, Handheld is OK 
400   f8        1/30     With image stabilization, handheld is marginal
400   f11       1/15     Need a tripod
100   f11       1/4      Need a tripod
200   f16       1/4      Need a tripod

You will need to decide if these are reasonable. See the Wikipedia article on Exposure Value for more information. With a larger or several lights, you should be able to get to EV 10 or 11.

enter image description here enter image description here

I am assuming a simple setup, if you want a pure white background, you will want separate lights pointing at a white background.

Note that the Color Rendering Index (CRI) of household LEDs isn't very good. If color accuracy is important you should use something else.

I shoot a lot of flowers in my house. I use a speedlight and a small softbox on one side, and a white foamcore reflector on the other side (very close). If I want a dramatic image, I often put another speedlite in the back for a rimlight (need to be careful to shield the lens from this light). I use cheap Yongnuo RF flash triggers instead of sync cords.

  • Off to price some proper spotlights. Thanks Nov 9 '19 at 14:51

Sunlight is exposure value = 15. It's about 100 000 lux.

So, with e.g. about 100 lux you get exposure value = 5, because every doubling of brightness increases exposure value by 1 and every halving of brightness reduces it by 1. 1000 is approximately 10 doublings (well, ok, to be exact, 10 doublings is 1024).

However, LED lights have their output specified in lumens, not in lux. The reason is simple. Lux measures the amount of light going to a square meter of a surface. You can't tell how many luxes one lumen is, because the environment modifies the light by scattering it around.

If you have a 100 lumen source, where the light goes only to a 1 square meter surface, you have 100 lux, or in other words, exposure value = 5. However, to get 100 lumens distributed to only 1 square meter surface needs some directionality. An omnidirectional LED with no light modifiers won't do it.

There's the sunny f/16 rule. With exposure value 15, you use ISO N, shutter speed 1/N and f/16. You can calculate the exposure from that. For example, with exposure value 5, if you use ISO 16N, shutter speed 1/N, f/2 (example: ISO 1600, shutter speed 1/100, f/2) you have the correct exposure.

To calculate how many luxes one lumen equates requires you to know how directional the light is. Lux is lumens per square meter. So, you need to know the full properties of the directionality of the light source.

  • So if I understand you correctly, unless the light source has some sort of focused beam its not possible to calculate the LED lumens required to obtain a specific exposure value Nov 8 '19 at 21:41
  • Well, if you know all of the details about the entire environment, how large the room is, how reflective the walls are, etc. you can calculate the scattered light level. And, if the LED light is very close to the subject, it may be possible to calculate the amount of direct light on the subject. But it won't be easy. I'd say it's much easier to do some very rough estimation, purchase a light having the roughly estimated lumen count, and then just accept that you have to use whatever exposure you need.
    – juhist
    Nov 8 '19 at 21:51

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