LED lights in exhibition cases

Karen Potje <kpotje [at] cca__qc__ca> writes

>...  Is information about the
>UV content of white LEDs available?  Is it possible to control the
>light levels and ensure that they remain at a steady 50 lux  over
>the course of a long (8 month) exhibition? Do LED lights start out
>bright and then get dimmer over time? ...

Due to the physics of the generation of the light, there cannot be
any UV output at all. All the light is concentrated at the
wavelength that shows the LED's predominant colour. White light
obtained by LEDs is actually simulated to the eye by mixing the
output of differently coloured LEDs. Remember that visible light
also has a deteriorating action on materials. Automatic adjustment
of light levels is quite feasible.

In comment Mary Fahey wrote:

>In 1999 a large hallway in Henry Ford Museum was renovated ...
> ...

> ... The first
>batch of lights consisted of a mixture of white and yellow LED's
>used in combination to produce an aesthetically acceptable color.
>The light bulbs were configured for use in existing screw-based
>sockets. The bulbs (part #R-123-OYW-120AS) were purchased for $250
>each and were guaranteed to last for 2 years. Within the first year
>all of the bulbs grew dim, malfunctioned and "blew out".
> ...
>
>The supplier recently provided replacement bulbs for both exhibits
>along with the following explanation: "the combination of white and
>yellow LED's drew different amperages which caused the LED's to
>short each other out". ...

This is flawed electrical design, possibly individual series
resistors could have prevented this.

>The replacement bulbs ...
>utilize LED's that are homogeneous in color and provide a much
>improved color for the display of artifacts. ...
> ...
> ... I was unable to
>detect the presence of any UV radiation using a Crawford UV monitor.

There will be none at all. Kind regards,

George Brock-Nannestad


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                  Conservation DistList Instance 17:35
                 Distributed: Friday, October 17, 2003
                       Message Id: cdl-17-35-001
                                  ***