How to center two lamps over a rectangular table

Say you have two lamps that you want to hang over a rectangular table. What should the distance be between them?



My intuition was to hang them at either a quarter of the length in from either side, with 1/2 the length of the table between them, the logic being that they’d then be centered over each their own half, thus giving roughly equal amounts of light to across the table.



Another attempt was to hang them 1/3rd in from each end, with another 1/3rd between them, the logic being that it’s equal distance.



As it turns out, the correct answer is neither. The correct answer is to hang it 3/10ths in from each end, with 4/10ths between them. So if your table is 2 meters or 200cm long, you would hang it with 60cm from edge to each lamp, and 80cm between the lamps (measuring from the center of the lamp, or the wire, not the rim). Similarly if your table, as ours, is 180cm, it’d be 56cm from each end, and 72cm between lamps.



How did I find this out? I asked my in-laws. Seriously, my mother-in-law recently got a pair of lamps hung over a rectangular table by a professional, and he used some formula, which she didn’t catch. So she offered to measure the distances. Her table was 2 meters. You get the picture.



This is all a matter of taste and subjectivity, of course, but we like the result.

10 comments

Note to self: Never hang two lamps above one table.
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Wouldn't it depend on how high the lamps are from the table?
By Guan Yang on Thu, Dec 28, 06 at 15:52 · Reply
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Reverse engineering. Nice.
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@Guan: No idea, we hung them high enough to not be in the way when looking at the person across the table and low enough to not blind. I guess not blocking the view might be a good reason to not hang them 1/4th way in from the edges.
By Lars Pind on Thu, Dec 28, 06 at 15:52 · Reply
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Agree with Guan. It depends on how far above the table the lamps are.
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@Guan, Robin: How would it depend on the height? If it's higher, they would go further apart and closer to the edges, or the opposite?
By Lars Pind on Thu, Dec 28, 06 at 15:52 · Reply
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Hmmm. I might have incorrectly assumed that your lights shine down to illuminate the table and as such lights have illumination angles, this would affect the spread of light on the table. This is consistent with your comment above, but we're still none the wiser about the type of lamps :o)
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They do shine down, of course. That should mean that if you hang them higher, it matters less where exactly they hang, as they'll light up the entire surface anyway, no? Conversely, if they're so close they can't light up the entire table surface, it won't matter what distance you hang them at, either? It doesn't say that they should be either closer together or further apart? Basically, this is about aesthetics as much as anything. We're assuming there's some wiggle room within which the entire surface is being lit, this is about finding the distance that looks the best, with the lamps neither too close nor too far apart to look silly.
By Lars Pind on Thu, Dec 28, 06 at 15:52 · Reply
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To answer your question, hanging them higher means it matters less, but you're going to run the risk of illuminating people's eyes rather than the table. Also, if they are too high above the table, then the table won't have enough concentration of light. So, it matters how high the lamps are. Funnily enough we have been working on a lighting layout for our house and face some of the same issues. We have two pendants above a 3m table in a 3.5m space. Now, directional pendants *tend* to either shine in people's eyes or need to be so low as to get in the way, so we're going to use general pendants.
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To answer your question, hanging them higher means it matters less, but you're going to run the risk of illuminating people's eyes rather than the table. Also, if they are too high above the table, then the table won't have enough concentration of light. So, it matters how high the lamps are. Funnily enough we have been working on a lighting layout for our house and face some of the same issues. We have two pendants above a 3m table in a 3.5m space. Now, directional pendants *tend* to either shine in people's eyes or need to be so low as to get in the way, so we're going to use general pendants.
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