telling when an led is bad?

[coralbeauties]

I bought a piece of crap diy led light. I removed all of them and have tested and set aside which ones would light. several of them were unglued and have gotten so hot the star board is discolored. He glued on some optics and looks as if there is some glue on some of the lens. some of the lens look cloudy. How do you tell if the led will be worthless to mount? They all will fire but if the lens are damaged is the output really reduced? what is the best way to attach the optics?
thanks
Jeff

 

[dacianb]

What types of LEDs are you talking about? There are LEDs with silicone primary lens and leds with polycarbonate one (touch it with your fingernail - if is rather rubber like or rigid plastic)
If the LEDs are so hot than the board colored, this mean that the chip of LED is even in worst shape. Much lower light output and spectrum shifts.
Glue on lens means light output in that particular area is very low (you can judge how badly the output is reduced by size of the glue spot). White smoked lenses - are probably smoked lenses, as they look like. That chip is in coma anyway, so throw it away. For silicone lenses (which handle higher temperatures) smoking look is not due to high temperature, but rather glue fumes (silicone absorbs easily chemicals floating around). But they also have reduced output already.

As a reference, touching with your finger the lens of a led will lower the output with approx 10-20% (depend how greasy your fingerprints are).
Never use superglues or such fast curing aggressive glues near your leds. Best way to glue optics is with silicone and leave it curing for 24-48 hours before starting the light.

 

[coralbeauties]

Tks for the reply. I thought that was what I was going to hear. They are all cree LEDs for what it is worth. If the lens are indeed bad cane they be removed and then optics put on?
Jeff

 

[dacianb]

Normally yes depend how they are glued. But i was talking about the primary lens - tiny bubble on the chip itself.

 

[dacianb]

I dont use any optics but bare leds and looks better.

 

[coralbeauties]

Normally yes depend how they are glued. But i was talking about the primary lens - tiny bubble on the chip itself.

so if the lens is cloudy or has glue on it I can try and remove it and still will have full strength of the led? I am trying to salvage as many as I can. I thought I was getting a pretty good deal but after getting everything pulled apart I am not thinking so. the whites that came with it are all over the place on color, some pretty white and others yellow, poor binning, they were purchased from rapid.
thanks
jeff

 

[dacianb]

so if the lens is cloudy or has glue on it I can try and remove it and still will have full strength of the led? I am trying to salvage as many as I can. I thought I was getting a pretty good deal but after getting everything pulled apart I am not thinking so. the whites that came with it are all over the place on color, some pretty white and others yellow, poor binning, they were purchased from rapid.
thanks
jeff

Can you send some pics?? It is hard to get the full picture. Normally LEDs have to be well cooled to keep their parameters over time. Specially CREE are rather weak leds to stress (temperature / current)

 

[coralbeauties]

Here are some pics of several bad leds. Both have been overheated and the lens on one looks crystallized, the other the lens has come off. I believe they are royal blues. The third pic is of an led I would like to know if anyone knows what led it is. It is blue but I dont think it is a royal blue.
thanks
jeff

 

[dacianb]

I am afraid that doesnt worth to keep them. Are so badly damaged that you dont know anymore what spectrum or intensity provide. Call them dead and burry them to not turn to zombies ☺

 

[coralbeauties]

I pretty much figured that. Any idea what the white colored one might be. It is a blue spectrum
Tks
Jeff

 

[dacianb]

I pretty much figured that. Any idea what the white colored one might be. It is a blue spectrum
Tks
Jeff

Most probably fumes absorbed by silicone lens. Still will not behave normally. If will look with a large magnifier at the chip itself should be not a perfect sharp square anymore but should look as the coating on it melted a bit and started flowing. Such leds have shifted spectral emission really bad.
When build a new light use large heatsinks and power fans. If leds are rated for 1 amp, use them at max 0,7 ( specially cree). With all leds on at max power, after half hour touch the board of each led- if can keep your finger there it is good for leds. If is HOT will need more cooling or less current on leds.
In my lights (180 w each module) I am using thermostats to start the fan at 40deg C but also safety thermal switch at 80C in case of fan failure. Still led board stays at a temperature colder than my hand. And i am using 2A leds at max 1A power.