One techincal issue to be aware of.  Color temperature of a light source and CRI (color rendering index) are not the same thing.  Color temperature is an expression of the various wavelengths of the visible light spectrum present in a particular light source, generally expressed as degrees Kelvin.  For example, "standard" daylight is generally interpreted to be somewhere between 5,500 (a bit on the red end of the spectrum) and 6,500 (a bit on the blue end) degrees K.  CRI is how accurately an artificial light source matches a light standard, usually sunlight.  Different light sources of the same color temperature, say 6,000 degrees K, can have widely varying CRIs.  Thus it is not adequate information for a manufacturer to list only a color temperature that is in the daylight range.  The light source can still be very inaccurate or unpleasant, even if it is at the desired color temperature.  A CRI over 90, and ideally over 95, is desirable.  This information is usually available on the manufacturer's web site, if it is not on the bulb's package.

Marc Williams
---- Paul Fritz <[log in to unmask]> wrote: 
> Wendy,
> 
> That is wonderful information.  I look forward to seeing the documentation.
> 
> Additional note:
> 
> There are LEDs just recently entering the market that are rated in 
> excess of 60,000 hours life span with very little if any light drop. 
> 
> The biggest problem I've seen from I believe is related to the CRI.  The 
> temperature of the light (not actual heat) is often skewed toward the 
> cooler temp which results in a blue-white light that can be interpreted 
> as harsh by visitors.  Most of the LED manufacturers I've looked at 
> recently offer the kelvin temp for the bulbs, so you can look for one 
> with the correct temp.
> 
> Luxeon LEDs are interesting in that they put out as many lumens as a 
> halogen lamp with only one bulb.  They do tend to run warm, though not 
> as warm as a halogen. 
> 
> Again, I look forward to hearing from others on this.  Isn't there an 
> lighting company who occasionally posts to the list?
> 
> Paul Fritz
> 
> Wendy Claire Jessup wrote:
> >
> > Greetings:
> >
> >  
> >
> > The American Institute for Conservation presented an excellent two-day 
> > workshop on Exhibition Lighting as part of its annual meeting last 
> > month.  The workshop presented a lot of really good information, 
> > including information about compact fluorescents and LEDs. 
> >
> >  
> >
> > Stefan Michalski of the Canadian Conservation Institute presented a 
> > table that provided the general characteristics of light sources and 
> > compared all of the sources that are available.  With respect to UV 
> > emissions, compact fluorescents will emit between 100 -- 150 
> > microwatts/lumen of UV while white LED (light emitting diodes) emit 
> > between 0-75 microwatts/lumen.  For compact fluorescents a custom made 
> > filter will be necessary while filters are not required for LEDs.
> >
> >  
> >
> > Both types of illumination are very useful at short distances such as 
> > in display cases and relamping frequency is relatively low.  But there 
> > are drawbacks with both types of lamps:  Compact fluorescents are not 
> > easily directed in a sharp beam and although the LEDs can be easily 
> > aimed there are still technical problems that make them a challenge 
> > for use in many museums. 
> >
> >  
> >
> > These technical problems, cited in Stefan's chart, and discussed in an 
> > excellent presentation by Richard Kerschner, the head of conservation 
> > at the Shelburne Museum in Vermont, include problems with the color 
> > rendering index (CRI) which varies from 70 (fair) for current all 
> > white lamps to 90 (good) for mixed color LEDs (although the white 
> > lamps are expected to improve over the next few years); variable lamp 
> > lifetime; a drop of lamp intensity early in the lifetime of the lamp; 
> > and poor color homogeneity of the beam.
> >
> >  
> >
> > Although a good portion of the 2-day workshop was devoted to the 
> > technical issues associated with lighting (energy conservation, 
> > applications, etc.) including potential damage to museum collections, 
> > there was a considerable amount of information presented and 
> > discussion about visual perception, visual noise, viewer needs and 
> > expectations, and the aesthetic impact of lighting.  
> >
> >  
> >
> > At this point, I can't remember if the proceedings will be made 
> > available via the web or in other formats.  I have a call in to the 
> > AIC office to see if they can provide additional information about 
> > dissemination of any or all of the proceedings.  Once I hear, I will 
> > post the answer to Museum-L.
> >
> >  
> >
> > Hope this helps.
> >
> >  
> >
> > Wendy
> >
> > Conservator
> >
> >  
> >
> > Wendy Jessup and Associates, Inc.
> >
> > Care of Cultural Property
> >
> > 933 N. Kenmore Street, Suite 323
> >
> > Arlington, VA 22207
> >
> > (703) 522-2801
> >
> > Fax: (703) 522-2802
> >
> > www.collectioncare.com <http://www.collectioncare.com>
> >
> > ------------------------------------------------------------------------
> >
> > *From:* Museum discussion list [mailto:[log in to unmask]] 
> > *On Behalf Of *Paul Fritz
> > *Sent:* Tuesday, May 01, 2007 10:23 AM
> > *Subject:* Re: UV light emissions from Compact Fluorescent lights
> >
> >  
> >
> > It is my understanding that fluorescent lamps rely on UV to work, so 
> > they would put out enormous amounts of UV light.  That being said, 
> > they use phosphors to convert the UV to visible light, and how much 
> > escapes is something I don't know.
> >
> > I'd recommend going with LED lighting rather than UV as it can be made 
> > UV neutral and is much more efficient than fluorescent lamps.
> >
> > -- 
> > *Paul C. Fritz*
> > *Pamplin Historical Park & the National Museum of the Civil War Soldier
> > **6125 Boydton Plank Road*
> > *Petersburg**, VA 23803*
> > *(804) 861-2408 -- Tel
> > (804) 861-2820 -- fax
> > /Visit us at/
> > www.PamplinPark.org <http://www.pamplinpark.org> *
> >
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> > Subscriber Information:
> >
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> 
> -- 
> *Paul C. Fritz*
> **Pamplin Historical Park & the National Museum of the Civil War Soldier*
> 6125 Boydton Plank Road
> Petersburg, VA 23803
> (804) 861-2408 -- Tel
> (804) 861-2820 -- fax
> /Visit us at/
> www.PamplinPark.org <http://www.pamplinpark.org> *
> 
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> 
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