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Lighting Information: LED's, UV and IR

Sacred Darkness:
Sculptural Fabrications of Story and Place
Feb 1st to Mar 15, 2001

I wasn't consciously attempting to use as much bandwidth as possible in this show, but it turns out that I did a pretty good job! I have used white light (the combined visible spectra) and both infrared and ultraviolet light sources from both ends (and slightly beyond)of what is called the visible part of the spectrum. I am fully aware that even with this I have only covered a minute part of the full electromagnetic spectrum. Maybe the next show will make an attempt to cover more! While this is an art show and technical concerns take a secondary place, I want to share some of those concerns here. I've been involved with electronics since around 1956, but have never used much of this knowledge until this show.

As far as I can tell from my research, this show is the first time super bright, white LED's (light emitting diodes) have been used exclusively to light an art gallery show. LED's are more familiar to us as those small, red and green indicator light on consumer electronics. White LED's are a more recent discovery and are said to be color corrected for 6500 degrees Kelvin which is very close to daylight. I haven't counted precisely, but believe that I have over 200 white LED's in fixtures, over 50 red LED's as part of the installation, 20 Yellow LED's in the entrance and a few green LED's as safety markers.

Due to the low light and especially the low ambient light in the show, an infrared security system was also developed by the artist. The 6 IR LED's on the camera were augmented by 72 more on 2 IR illuminator circuit boards.

The large name at the rear of the gallery is lighted using a single, 48" ultraviolet fluorescent tube. The lighter part of the name is 1/2" styrofoam insulation sheet masked with black paper. Intended to be subtle for the viewer, in installation photo it reads as a very luxuriant blue-violet.

LED Technical Information

Using 5.0 volt switching power supplies
( Jameco 171707)
All LEDs powered by resistor networks

LED's are current rather than voltage devices. Series, current limiting resistors are important to keep currents in the working range for each LED. Ohms law is used to determine resistor values for any DC voltage. For example, I chose to use a 5 volt DC switching power supply and the white LED's working current range is near 0.02 Amps. I read that keeping current slightly lower than the listed value would insure long life. I also wanted to buy common resistor values so here is how I came up with resistor values using Ohms law:
5.0 supply voltage minus LED voltage drop (5.0 - 3.6) = 1.4V
E/I X R = 1.4/0.09I = 90 Ohms
And luckily I found resistor networks at 90 Ohms!

One 5 Volt power supply is more than enough for my 250 or so LED's. I ran a buss of number 16-22 wire throughout the gallery and I am sure some runs are over 100 feet long. I never experienced the LED's dim due to Voltage drop.

The following is as much a reminder for me as it is general information.

White LEDs

3.6v drop (Sloan SL905WC-13, 3700mcd)
5.0 - 3.6 = 1.4v
70 ohm = 20ma
90 ohm = 16ma

Red LEDs

1.9v drop( Ledtech LT1873-UR-C07, 2112mcd)( Jameco # 156970)
5.0 - 1.9 = 3.1 v
155 ohm = 20ma
220 ohm = 14ma

Yellow LEDs

2.4v drop (Ledtech LT2K33-URP-8, 9300mcd )(Jameco # 153146)
5.0 - 2.4 = 2.6v
150 ohm = 17ma
130 ohm = 20ma

Green LEDs

2.2 v drop( Ledtech LT1823-81-HE, 500mcd)(Jameco # 156961)
5.0 - 2.2 = 2.8v
140 ohm = 20ma
155 ohm = 18ma

Here is a new addition--a great LED flashlight page with loads of info:
Brock's LED Flashlight page
Updated: 26 Feb 2001