Museum Lighting? What white point?

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Cliff Wilson

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Customer came in and asked some lighting questions.

He has installed track for two walls in an area that will be his "gallery."

We talked a while about color temperature and white points, of which he was surprisingly knowledgable.

I explained that "true color" was not an absolute, but was based on the viewing conditions and specifically the degrees Kelvin of the light. He asked, "What lighting would a museum use?"

I didn't know, do you?

Thanks!
 
I will hazard a guess ...5500 degrees Kelvin which simulates high noon.
 
A “hazard” guess different from Dave:

I would guess it is closer to 4800° K – more towards incandescent than sunlight. It would give a warmer view than 5500° K. and maybe contain less in the UV spectrum.

… but, its a guess.
 
See now, a typical light booth for photo/image viewing is at 5200, which (as I understand it) provides the human eye with the largest spectrum, that would have been my guess.

But, the more I thought about it, the more I just wasn't sure? Would they try to simulate a warmer "candle glow" so it would be more like the light old masters would have been displayed in? Daylight?

I remember talking to a conservator that said the museum she worked for put UV filters on their lighting and made sure it was OFF as much as possible, so that is probably not at issue.
 
Hugh, do you know the white point of the lighting? Is there a particular bulb that is used in an MR16 fixture?

I'll go search on MR 16, but thought I'd ask in case I can't find them. ;)

OK, went and did a search. MR 16 are halogen based fixtures and could have any halogen bulb in them. So, the color temperature is still in question?
 
Here we go with the whole "Museum" thing again. I understand that your client wants to display the work in the "best light possible" but please don't throw the "museum" thing into the equation. (I really think we are doing a disservice to our trade with the "custom framed to Museum standards","Museum glass" moniker).

If so, you should probably be concerned (more so) with LUX or footcandles of light than the color temperature. Most museum shows would/are considered by many to be "under" lit because the museum is rightfully more concerned with the cumulative effect of exposure to light than the color temperature.

Cliff, the answer to your question is not as easy as just specifying a color temperature.

I don't care what kind of light source you use, if you run the lamp at less than 100% output (in our gallery we use 130 volt lamps to get longer life but sacrifice getting a "dimmer" color shifted output) you will not get a true color rendering. And the "convenient" way to get lower output is to put a dimmer on the circuit. If so, the color will shift from whatever you start with to a more yellow spectrum.

MR-16 lamps come in a whole host of options: First, they run on 12 volts, so either the track being used needs to be at 12 volts by using a transformer whose capacity at 80% is large enough to power the number of lamps at the calculated wattage being used, or the track heads need to have a 12 volt transformer in each. Next, you need to determine the appropriate WATTAGE of each lamp, 20, 35, 50 or 75 (if the fixture can handle 75 watts). Also remember that they run HOT so proximity to the ceiling/drapes etc is important. Also, they should not be run in the draft of an AC/heating vent. Then you need to determine the beam spread of the lamp, which can be 10 degrees up (spot to flood). Then you need to determine the color temperature of the lamp and the cover glass (clear/frosted) and finally, what the heat/uv and back of the lamp are doing as they will send light out the front and some will come out the back. The fixture (what is holding the bulb) will also contribute to this consideration. Also, if the fixtures use an ELECTRONIC transformer, then the dimmer associated with the circuit needs to handle an electronic load. If you are using a magnetic transformer/fixtures, then you need a dimmer who can handle a MAGNETIC load.

So, if your client's intent is to "see" the work, but also have comfortable ambient light, 3800K lamps at full intensity may be fine. 5000k is more operating room/color checking color and in my opinion is too white, but dimmed, may be fine.

Not only the lamps, but beam spread/width, focus angle and proximity are also as important than the color temperature of the lamp. Also, the "overlap" of the beam spread. Does your customer want a "even" spread? If so, then the DURA line of frosted lenses on MR-16 lamps may be what you are looking for. We have a narrow hallway with 8' ceilings and the frosted lenses makes for a more even dispersion on the walls. In our entry hall, we went with PAR 30 (line voltage) lamps which give an entirely different feel.

Then there is also the "effect" of the back of the lamp on the ceiling. Does you client mind seeing a "pattern" on the ceiling from the throw-off of the lamp? If so, is it OK to be purpleish, or do you want nothing and need a sealed back MR-16?

I would suggest getting the fixtures in the proper location with the proper aiming angle (30 degrees), then trying a few lamps to see what color temperature "feels" right in the environment. Also, what is being lit? Contemporary works look better in whiter light. Traditional works and crafts "like" a warmer feel.

I hate to say this, but this is why there are "lighting consultants" who make their living knowing this stuff.........
 
I agree with everything you said, Rob. But maybe we can boil it down a little....

In the real world, what difference does it make?
 
OK, <sigh>, believe it or not we discussed most of that, Rob. In much that way.

The client is a "high-end" general contractor. He has built "gallery areas" for his clients, and usually lets them worry about the bulbs.
For his installation, he has installed three tracks of light in this "gallery" area.
Two for ambient, and one for "wall illumination." All are on dimmers. He had a lighting specialist in. Angles have been calculated, wattage and voltage taken into consideration ... blah blah blah to the tune of over an hour of discussion.

They have been experimenting with the "ambient tracks" and have settled on bulbs at about 4600 Kelvin (sorry I don't remember the rest of the specs.)

He asked what I would recommend for wall illumination and I gave him the "it depends ..." speech. He asked what do museums do. I said I'd ask.

Jim, "In the real world, what difference does it make?"
Only the difference that the customer asked and I'd like to be able to tell him.

If the answer is "they don't worry about the white point of the light." Fine. But, I guess I'm surprised if that is the answer.
 
Your response to the "what do Museums Do" question is that they are less concerned with the color of the light and more with the amount of light, and at the light levels they use, the color temperature of the light doesn't really matter because it is difficult to determine the color at such low levels.

That is why I tried to move the discussion away from "Musuem" to "what temperature would the art look best under" discussion.

And, Jim for some of us it does matter. Hopefully someday you and Gail will come see what Barbara and I have done with our house and see the lighting we have done.

Just for ambient light (and doing so under California Title 24 specs) we had to find a combination of specular tirm and lamp (new Halogena 60 watt BR30 lamps whose lumen output is greater than a standard 65 watt R30 and whose CRI is whiter than standard halogen combined with a clear specular (silver reflective) trim.). That combined with MR11, MR16, PAR 30 and T-20 and T50 lamps and their associated fixtures which include cable, track and recessed.

OK I'll admit it, I am a lighting junkie.
 
Thanks for the invitation, Rob. One of these days, we'll come knocking on your door -- I promise.

I apologize for that "real world" comment. I really didn't mean to belittle the importance of lighting. I used to engineer industrial lighting systems and I have some knowledge about lighting of all kinds.

The point I failed to make is that in most residential situations, and certainly in all commercial situations, lighting may be almost uncontrollable. Ambient light comes from all directions in the typical house -- especially the new ones with more windows. Illumination spills over from artificial lighting in other rooms. It is very difficult to eliminate reflections in most homes. And in commercial buildings, the goal is to have equal illumination in every corner of every room. We used to call that the "general light level".

To put a point on it, in terms of color rendition and quality of illumination, the visual difference between 4000 degrees Kelvin and 5000 degrees Kelvin is probably affected more by reflected wall, floor, and ceiling colors than by the light sources themselves.

If your customer wants museum quality lighting, that involves a great deal more than light temperature, Color Rendering Index, and lumens. Not only lamps, but fixtures and literally everything within view of the art needs to be considered.
 
Rob Markoff said:
I hate to say this, but this is why there are "lighting consultants" who make their living knowing this stuff.........
Click to expand...

This is the only proper advice I can realy gleen from this whole topic. I undesrstand your desire to be able to help your client and it seems you have much to offer him in knowledge. At the end of your conversation you should realy suggest that they go see a qualified lighting specialist. If you don't want to leave your client hanging then make a point of tracking down one who has a wide knowledge of lighting of fine art. It shouldn't be that hard to make a few calls to get the best one in your particualr area.

I know it is hard to give up control of a client in this manner but at the end of the day what will make your client happier? Making a deciscion on lighting based on your thoughts on the topic or making a decision on sound reccomendations by an expert. Your client will remember you better for providing him with sound advice over educated assumptions.
 
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