Anyone using Violet LEDs - Burning Optics

[zachts]

This is a question to anyone who has been using Violet 420nm LEDs such as the ones sold by RapidLED. I have the fixture pictured runing on a massive fan cooled heatsink which stays totaly cool to the touch with the fan on and only gets up to 115 degrees with the fan turned off. All LEDs are runing at around 600ma. The fixture has only been up and runing since February 25th.

The violet LEDs have totaly burned up the little optics that come on them and started to brown the secondary Lenses as well. I've read that Bridgelux LEDs should only be ran up to 500ma unless you have a very good heatsink which I do. Now since none of the other LEDs are burning thier optics, (the whites apear to have degraded the phosphor a tad but not damaged the optics), I am leaning towards this not haveing anything to do with heat from the LED and more to do with the near UV Light they emit degrading the plastic.

Thoughts?

Anyone have this happen who is running violets at currents lower than 500ma.

 

[zachts]

Here are pics of what I'm talking about. Guess which ones are the violets. You can also see the tiny dark spots in the whites where the phosphor is starting to degrade.

After picking off the burnt optics they LEDs are just as bright as they were originally and apear otherwise undamaged.

 

[jwoyshnar]

I run them. I don't see anything like that. Mine still look like new. I'm running mine at 700ma

 

[zachts]

How long have they been running and what are you using for cooling? I'm seeing the same thing on all my violets and I have some from Aquastyle, RapidLED, and the other main retailer of LEDs.

 

[WSPepsilon]

hmm that's a bummer... if it's the UV rays doing this i bet the only way around it is a glass optic bet that'll be expensive

 

[6Speed]

I don't want to sidetrack thread but I really like the round heatsink. where did you get it?

 

[zachts]

I don't want to sidetrack thread but I really like the round heatsink. where did you get it?

No worries, Nuventix from digikey. 40w par30 version. They make a pretty slick cooling device also but I just cheeped out and screwed a 60mm fan to it.

 

[kcress]

UV only goes thru some material. It doesn't go thru normal glass. That means the watts of light that's supposed be spewing out is instead dumping its energy into the optics.

 

[dublo8]

Been running the same ones and have not seen any degradation of any sorts.

 

[6Speed]

No worries, Nuventix from digikey. 40w par30 version. They make a pretty slick cooling device also but I just cheeped out and screwed a 60mm fan to it.

very nice. do you have any pics of it hanging over tank?

 

[zachts]

Been running the same ones and have not seen any degradation of any sorts.

what current are you running them at and on what for heatsinks? Details please, I'm trying to determine why mine are burning like this and other peoples aren't. Thanks.

 

[ghellin]

Mine are at 700mA with no problems. Passive cooling on 10"x1" heatsinks 4 or 5 LEDs per heatsink.

 

[kcress]

zachts; Are you using heatsink grease? If the LED can't dump its heat that would certainly contribute to optics roasting.

To burn up "optics" I'm guessing they're plastic.

Think about new cars with their crappy plastic headlight covers. Notice how they all turn yellow, craze, and become opaque? Most of that is caused specifically by solar UV. Now, you come along and put an intense UV source up against some plastic that wasn't likely expected to have ANY UV put to it. As the UV starts damaging the plastic structure, more and more UV stops making it out thru the lens and starts ricocheting around inside. There it gets used in further destructive processes. Very quickly your lens is fried.

Keep in mind real UV does this to your eye structures too.

 

[zachts]

zachts; Are you using heatsink grease? If the LED can't dump its heat that would certainly contribute to optics roasting.

To burn up "optics" I'm guessing they're plastic.

Think about new cars with their crappy plastic headlight covers. Notice how they all turn yellow, craze, and become opaque? Most of that is caused specifically by solar UV. Now, you come along and put an intense UV source up against some plastic that wasn't likely expected to have ANY UV put to it. As the UV starts damaging the plastic structure, more and more UV stops making it out thru the lens and starts ricocheting around inside. There it gets used in further destructive processes. Very quickly your lens is fried.

Keep in mind real UV does this to your eye structures too.

Yeah but look at the pictures I posted this damage is the built in plastic optic of the LEDs straight from the manufacurture. when I snapped the burnt brown plastic dome off the work are good as new......

I'm hearing mixed reports of some people experiencing simmilar results and others not having this happen. I' seeing the same thing on Violets from RapidLED and Aquastyle, all Bridgelux LEDs. So, I'm trying to determine if its and inherint flaw inthe manufacure of all violet LEDs or just a fluke that I got bad ones from three different sources. You would think that the plastics used in the LED themselves would be UV stable, right? Evidently not, but that doesn't explain why some report no problems when running at near 700ma currents. Mine are only running at 600ma.

 

[zachts]

Mine are at 700mA with no problems. Passive cooling on 10"x1" heatsinks 4 or 5 LEDs per heatsink.

Which LEDs do you have, and how long have they been running? RapidLED, Aquastyle, etc? I have some on 12" by 7" by 1" fan cooled heatsink (24 LEDs total) and the violets are still burning at only 600ma. I noticed the damage after about 3 months.

 

[zachts]

very nice. do you have any pics of it hanging over tank?

my camera kind of sucks but here's the best Picture I've managed. the anemone has trippled in size since switching to this fixture and I rarely do any maintence on this tank.

 

[Sgtauto]

zachts; Are you using heatsink grease? If the LED can't dump its heat that would certainly contribute to optics roasting.

LEDs like all semiconductors need proper thermal management. So proper thermal soldering to the board and proper thermal vias in the board. In this case the board is the star. All out of the DIY control. But proper thermal grease is not and is a must. I see a goo coming out. Is this a good thermal conductive grease?
More isn't better. Just enough to eliminate all air gaps. As the grease has resistance to thermal flow. The thicker the more resistance.

 

[sfsuphysics]

UV only goes thru some material. It doesn't go thru normal glass.

The physicist in me needs to correct this a bit, glass is optically more dense for UV than visible light, UV will transmit through glass with the amount depending upon the thickness of the glass. Something as thick as a window it's fairly opaque to UV (not completely though, but pretty damn well), however I doubt the lenses used are any where as thick as a window... plus they aren't made of glass.

 

[zachts]

LEDs like all semiconductors need proper thermal management. So proper thermal soldering to the board and proper thermal vias in the board. In this case the board is the star. All out of the DIY control. But proper thermal grease is not and is a must. I see a goo coming out. Is this a good thermal conductive grease?

Thermal Grease is Ceramique 2 by Arctic Silver
Note that it is only the Violet LEDs that are burning not even the 660 red (one of the three in the center of the heatsink) which by the laws of physics should be creating more heat on the lens side of things.

 

[zachts]

The physicist in me needs to correct this a bit, glass is optically more dense for UV than visible light, UV will transmit through glass with the amount depending upon the thickness of the glass. Something as thick as a window it's fairly opaque to UV (not completely though, but pretty damn well), however I doubt the lenses used are any where as thick as a window... plus they aren't made of glass.

Look at the pictures, the lenses burning are the buit in ones. only a milimeter thick or so. and presumably made of acrylic or polycarbonate (the data sheets dont say). the secondary optics are typical 80 degree type optics as sold by all the LED retailers and even those were starting to yellow. I'm not sure if it was just transfer from the burnt primary optics or if the secondary lens them selves were starting to burn also. I removed th burnt primary optics with tweezers and replaced the secondary lenses, so we will see in a month or so if it really was the UV or not.

Hopefully more people chime in before then.

Thanks for all the input thus far!