Problems
NavUp
NavLeft NavRight

Color Is Too Cold

 

Each fixture has 54 white and 36 amber LEDs. The white LEDs give off a very cold light (approximately 8000K). The amber LEDs are supposed to offset this blue tint for a warmer white. However, even with the ratio of 2 amber for each 3 white LEDs, the light is still very cold. The amber LEDs emit only about one third of the light flux, compared with the white LEDs.

For testing purposes and as a temporary solution, a yellow gel was placed behind the front window. The arbitrarily picked hue was rather heavy on the yellow side. However, the light output was dramatically changed and was an eye-pleasing amber. Another lighter shade of yellow would have been better.

Filtering light coming from LEDs is not very smart since we are removing light energy from an already weak source. Film type gels are also not suited for outdoor use. A better solution would be by replacing the clear front windows with tinted acrylic.

In the grand scheme of things, the temporary or planned remedies for the color issue is academic by now as explained in the next chapter.

 

Reliability Questions


A total of 12 light fixtures employ 864 white and 576 amber LEDs. White LEDs are grouped into strings of 6 each while amber LEDs are grouped in strings of 9 each. That means the failure of an LED darkens an entire string of 6 or 9 LEDs.

I have observed a high failure rate among the white LEDs. It has reached a magnitude that is not acceptable and the entire project is in jeopardy. I do not have the forensic tools to analyze the failure mode. However, months of observations give me some ideas. The failure almost invariably starts with an LED beginning to blink at rate of maybe twice a second. Later, it will stop producing light and it interrupts the chain of 6 LEDs. After powering down, the sequence of being fully operational, blinking and going dark may repeat or the chain will remin dead.

Not a single amber LED has failed. Hundreds of the same white LEDs are also used indoors (24 hours a day under the kitchen cabinets) and several hundred blue, red and green LEDs are used indoors. The roughest service uses blue LEDs at the edge of the deck where rain splashes directly onto the LEDs. Not one has failed anywhere.

The failure is not caused by the LED chip. The blinking points to a bonding problem of the internal anode lead. It could be that the epoxy case of the white LEDs is not sealed properly or is not bonded securely to the external leads. In short, white LEDs fail in droves in a semi-protected outdoor environment. All other colors indoors/outdoors and white ones indoors are not affected.

 

 

It was time to throw in the towel. See the chapter on Luxeon.

 

[Home] [Introduction] [Electrical Design] [Physical Design] [Problems] [Luxeon LEDs] [Luxeon Assembly] [Results] [Bollards] [Improvements]