Kathie,

 

Your question actually has more facets than just color temperature.  A color temperature of 2700K is on the very warm (yellow/orange) side, somewhat equivalent to sunlight at sunrise or sunset.  "True" daylight is considered to be around 5500K, which is definitely on the cooler or bluer side, somewhat equivalent to sunlight at high noon.  Perhaps more important than color temperature is CRI, or color rendering index.  This is how closely a light source replicates sunlight at that color temperature.  Ideally, you want a CRI very near 100, which would indicate it replicates it almost perfectly.  Incandescent lamps (the correct term according to the industry for a light source, rather than bulbs) commonly used for lighting museums (the MR-16, for example) are available in CRI of 96+.  A lamp with a CRI of 80 would be considered woefully inadequate.

 

So, the first thing to ask the manufacturer of the lamp (not the vendor) is what is the CRI?  Ideally, they also can provide you with a spectral curve of the lamp.  This shows the light emitted at each wavelength, ideally compared to natural sunlight.  It also will show if there is any UV light present, which there should not be - if there is, that is not the lamp you want.  LEDs have progressed a lot in the last few years, and technically, it should be possible to fine-tune them to be near 100 CRI.  Whether specific manufacturers have done this is something you will have to ascertain.  Due to the progression in technology, advice from 2012 such as the Getty publication may no longer be relevant.  For your application, just buying an off-the-shelf fixture made for the general public probably will not be ideal.  You should look for ones that promote their color accuracy on their packages and in their literature.  If they are simply promoting energy savings and long life, they probably have poor CRIs.  But this can only be determined with CRI ratings and spectral curves from the lamp manufacturers.  Complicating this further is the fact that the manufacturer of the fixture may or may not be the manufacturer of the LED lamps in the fixture.  So some sleuthing may be necessary

 

To answer your question about what color temperature would look best (assuming you have found high CRI lamps), the best information I am aware of about that was testing done with high CRI MR-16 lamps in an actual museum setting.  Regular visitors were asked to look at objects illuminated with different color temperatures between about 2700K and 5500K.  They were asked to indicate which lamp produced the most "natural" colors.  Thus, this was clearly subjective, but also real-world  for museum viewing.  The color temperature that was found the most natural was 3500K.  It can be assumed that this would translate to LEDs that also are of high CRIs.

 

Many other factors influence perceived color, including the color temperature and CRI of nearby lighting.  A 3500K display case in a room filled with 5500K overall lighting may appear too yellow/orange, for example.  Also remember that light intensity on the objects in the case is important even if it is LED lighting.  Select fixtures or combinations of lamps that keeps the light levels in the desired range for the types of objects within the case.

 

Marc

American Conservation Consortium, Ltd.
     4 Rockville Road
     Broad Brook, CT 06016
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From: [log in to unmask]" href="mailto:[log in to unmask]" target="_blank">Kathie Gow

Sent: Wednesday, January 23, 2019 4:48 PM

To: [log in to unmask]" href="mailto:[log in to unmask]" target="_blank">[log in to unmask]

Subject: [MUSEUM-L] best color temperature for new LED lights?

Hi Listers. We are replacing our 8-foot-long fluorescent tube light fixtures in two large display cases (due to a smelly blown-out ballast!), with new LED fixtures, and I need to decide the color temp of the new lights. I am thinking we want warm light, but something that will still show whites as white. Would 2700K do the trick?

(We are a small historical society museum with lots of oak and other wood cases, whitish walls (that are mostly covered) and some exterior LED fixtures that have cooler light...

Happy for all LED lighting tips and things you've learned!

best,

--Kathie

Kathie Gow

Curator, Hatfield Historical Museum     hatfieldhistory.weebly.com

Oral History Producer     wordspicturesstories.com

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