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February 27, 2005 4:16 PM

Why do incandescent light bulbs make my pale yellow walls look completely white?

I recently painted the walls of my apartment a pale yellow with a green undertones (B.Moore's Stanhope Yellow). The walls look wonderful in natural light, but when the room is lit with incandescent soft white lamp light placed near a wall, said wall turns almost white (and turns completely white with a GE Reveal light bulb); the wall ~12 feet away from the light source remains the desired yellow. This whitening effect is less so with halogen lighting.

Since daylight is brighter than the incandescent lighting, what is going on here, and how can I avoid the "white-out" effect? And why would a bright halogen light source, halogen known for being very white light, not whiten the walls?

posted by ParisParamus to science & nature (23 comments total)

I don't know why or how all that lighting stuff works, but I do know that my artist wife swears by Full Spectrum lighting. You can find bulbs for almost any need, and the color is wonderful. The regular sized bulbs range from $10 - $20 each, but claim to last up to 12X times the life of a regular bulb. they even have bulbs to replace fluorescent tubes...worth a try.
posted by lobstah at 4:54 PM on February 27, 2005

This has to do with color temperature. You might also find out more about the subject by perusing cinematography-related sites, since this is a major issue in filmmaking.
posted by Dr. Wu at 4:58 PM on February 27, 2005

I don't believe the issue is with color temperature, even though it might seem a likely culprit. In darker light, your eyes register light intensity better than light color. Tungsten light is generally very low in raw light-output (in lumens), halogen is simply brighter (regardless of the color temperature). The limited color resolving power of the cones in your eyes is being swamped with yellow-orange light, making you "color blind" to the pale coloring on the walls.
posted by Civil_Disobedient at 5:00 PM on February 27, 2005

The filament of your incandescent bulb produces a yellow light. Casting that yellow, along with the brightness, tricks your brain into thinking that the wall is white. Your GE Reveal lights are still incandescent, but the glass is tinted blue to counteract some, but not all of the yellow. Here's a neat page that has a little mouse-over display of the different effects of different kinds of lightbulbs.
posted by crunchland at 5:01 PM on February 27, 2005

crunchland: that link is really nifty.
posted by Dr. Wu at 5:08 PM on February 27, 2005

Well, you will certainly have improved color rendering (i.e. the wall should appear more like the color it is) with halogen lighting because the presence of halogens allow the filament to glow hotter and brighter (the halogen forms a metal halide that returns tungsten to the filament when it breaks down at high temperature).

The filament of your incandescent bulb produces a yellow light. Casting that yellow, along with the brightness, tricks your brain into thinking that the wall is white.

Can you explain this any more, crunchland? In my experience if you want to enhance the colour of an item you illuminate it in light of the same color. The link you provide (very handy!) seems to back this up. Note the yellow wall bathed in yellow light. A fairly low wattage tungsten bulb should be pretty damned good at brining out the color of the walls .

I don't believe the issue is with color temperature, even though it might seem a likely culprit. In darker light, your eyes register light intensity better than light color.

Color rendering is much more at play than this effect you mention, Civil -- this only becomes an issue in very low levels (i.e. no lights on, curtains closed, night time). Remember that the further wall *does* appear yellow, and it is further away from the light -- by your reasoning it should appear less colored, not more.

Paris, just how close is your light to the wall in question? What type of light fitting are we talking about? Are there any objects near this wall? My guess is the sheer proxity of the fitting to the wall is having an exagerated brightening effect -- sure, a light bulb 4 metres high casts a yellow light, but take the same bulb and put it a foot away from a white piece of paper. It ain't yellow. It might be that you need several, less bright fittings to achieve the affect you desire. Lower the wattage of the bulbs you're using. If it works on the close by wall, repeat for the other walls.
posted by nthdegx at 6:16 PM on February 27, 2005

To expand on crunchland's point, and oversimplify: Let's say white light is made up of red, green and blue parts. A white wall reflects all three, and a yellow wall reflects only red and green. Under yellow light, which is made of red and green, both will reflect red, both will reflect green, but their will be no blue for either to reflect. Therefore the same light would hit your eyes from either, and you can't tell the difference. Essentially they end up guessing "white".
posted by cillit bang at 6:22 PM on February 27, 2005

No. In those conditions the yellow wall looks yellow and the white wall looks yellow.
posted by nthdegx at 6:30 PM on February 27, 2005

And then there's that nifty trick whereby one's eyes will translate discolouration back to true colour. Or, at least, their best guess as to true colour.
posted by five fresh fish at 8:33 PM on February 27, 2005

No, nthdegx. Yellow light may be entering your eyes, but since the brain mostly perceives colour in reference to other objects in the room, which are also yellow-tinted, it won't know that. The walls will look white.
posted by cillit bang at 10:01 PM on February 27, 2005

I'm with crunchland and cillit bang. That said, I think nthdegx's point may be valid under certain conditions. Conditions where there is some source of white light around to compare to, I guess. That would be consistent with PP's observations regarding daylight. (on preview, this would have been slightly less redundant if the server wasn't choking at the moment...)

Many people have been pointing out how easily the brain is fooled under specific lighting conditions.

PP, yellow, tee-hee!
posted by Chuckles at 11:24 PM on February 27, 2005

My bathroom is painted an aqua color. It looks blue when it's sunny outside. At night, with the incandescent lights on, it looks green. Q.E.D.
posted by kindall at 12:13 AM on February 28, 2005

So you're tell me that in a room with all red walls, floor and ceiling illuminated solely by a light source emitting red light, all the surfaces look white? If you shine yellow light on yellow objects they look yellow. You're drenching it in the color of light it is best at reflecting. I am not saying an illusion of some sort can never happen, but it contradicts all lighting theory I've read and is certainly the rare exception to the rule (if it occurs at all). Does anyone have any evidence?

My Thorn Lighting Technical Handbook (the only one to hand right now, alas) says the following on color rendition:

"Since a coloured object possesses the power to reflect certain parts of the spectrum of the incident light better than others, its colour appearance will depend on the spectral emission of the illuminant. For example, a blue sample will only look blue if there is blue energy in the incident light."

It's fundamental.

Paris -- photos of both light sources you're trying and their affect on the room would be really handy. Any chance you could fire some our way? If you'd like to email me feel free.
posted by nthdegx at 1:16 AM on February 28, 2005

*effect
posted by nthdegx at 1:17 AM on February 28, 2005

eyes (like everything else biological) don't measure absolute values; nor do they measure completely relative values. a completely red room can still look red, while a near-white wall appears white under certain lights, because eyes (brain) do a limited amount of relative correction.

the problem here is, as others have said, related to the light source not being "pure" white, but having a tint similar to the off-white wall. when the off-white light hits the off-white wall, off-white light is reflected/scattered and detected by your eye. so your eye receives off-white light from the off-white wall. when off-white light hits a white sheet of paper, off-white light is reflected ("white" meaning what comes in goes out), so again your eye receives off-white light.

now your brain/eye combination could decide that everything is off-white. instead, it assumes that the ambient illumination is "pure" white and so you interpret the off-white wall as white.

but the amount of self-correction is limited, so bright red won't be read as white.

it has to be this way because lighting conditions vary hugely. the eye is amazingly good at correcting for this to give you reliable information. a typical camera works over a much smaller range in brightness and shows colour casts with all kinds of different lighting conditions. and, of course, by being self-correcting it can correct for variations within eyes themselves.

oh, and many light sources are thermal you can describe the "off-whiteness" with a single parameter - temperature. that's why people mention colour temperature above. but this is just a conventient shorthand for describing "off-white" that assumes the light is produced in a certain way (it doesn't work for fluorescent tubes, for example).
posted by andrew cooke at 4:30 AM on February 28, 2005

Wow. This is a lot to digest pre-coffee. It's all very interesting (and I'm tempted to put it on my PDA and read it in the subway).

"It might be that you need several, less bright fittings to achieve the affect you desire."

The lamps are about a foot from the wall that goes white. The problem with dimmer lights is that the two 75 watt bulbs in question don't create that much light in the room.

My hunch is to go with as-bright, or even brighter sources, but much further from the walls (halogen spots from the ceiling, probably). But the idea was to having an incandescent lamp or two near my couch sounds/sounded appealing.

Any more thoughts on the full-spectrum light bulbs?
posted by ParisParamus at 4:39 AM on February 28, 2005

it's not brightness, it's colour. you can get daylight-spectrum incadescent bulbs in any art supplier.
posted by andrew cooke at 4:53 AM on February 28, 2005

You might also try the slightly blue-tinted bulbs made by GE or Philips. They are not quite daylight, but they're bluer than regular bulbs and should be available wherever bulbs are sold.
posted by kindall at 8:15 AM on February 28, 2005

This is why the fluorescent tubes used in the meat counter are different than the fluorescent tubes used elsewhere in the supermarket.

The meat counter ones emit a pinkish light to make the meat appear more red (look at it closely as you remove it, if it's packed) and they may emit some soft UV rays (although I'm not certain about that part).
posted by shepd at 9:09 AM on February 28, 2005

nthdegx: I have a pair of red-tinted sunglasses. For the first minute or two after I put these on, everything looks reddish. Then everything starts looking normal - maybe just a little bit more red than it ought to, but pretty much normal. When I take the glasses off, everything looks pale greenish-blue until my eyes adjust back. I have no trouble believing that my brain could pull the same trick with yellow-tinted light.
posted by Mars Saxman at 10:32 AM on February 28, 2005

I've been experimenting with the Verilux "sunshine in a box" natural spectrum lights and with plant-growth lights. The plant growing bulbs are really truly hideous, but they're pretty pure something -- they wash out a lot of colors for me, but they're also 150 watts, so maybe I'm just being blinded.

The Verilux makes everything... glow a little... red looks almost a bit purple? It's kind of trippy, though I'm not sure it's what I'd call "accurate" light. Still, a VAST improvement over the yellowing of regular bulbs. 60 watt, about 11.99 at my corner store, which means, away from the Manhattan markup, they're probably about 7 bucks.
posted by RJ Reynolds at 12:06 PM on February 28, 2005

Lighting a yellow wall with a blue bulb is a bad idea -- you want to enhance the color of the wall, or at least render it realistically. Using the wrong color light does not compensate -- it makes a mess -- dull hues. For all this talk of color theory (and again, pretty much everyone is contradicting all the reading I've done on the subject) there is (and I am speaking as a lighting designer here) absolutely no substitute at all for real world comparisons and tests: the nearest we can have to that is a photo -- there are so many factors here that we may not be considering. You can't compare incandescent bulbs with halogen bulbs without considering the luminaire too. If you're comparing a narrow beam for a wide beam that might make a major difference. If you were using 75W bulbs next to a wall compared to a halogen a long distance away, then I asssure the sheer proximity will override all our fanciful theories -- that's a very bright bulb to have a foot from the wall (and sort of fits my theory).
posted by nthdegx at 4:44 PM on March 2, 2005

You simply do *not* need natural spectrum lighting in a home environment. It's overkill. These things are fine tuned to be as precise to direct sunlight as possible and you'd be paying through the nose for a degree of fine-tuned color rendering that is of no use whatsoever: they're for very very specific uses. Likewise, the reason to use a halogen is not color rendering (in this case) -- it's because it'll give you the brightness you need/desire for your main lighting that perhaps an ordinary bulb wouldn't. How big is the room, incidentally? We're all guilty of wanting to sound like physicists here but we're missing the fundamentals.
posted by nthdegx at 4:55 PM on March 2, 2005