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