Lens Needs Glueing Back

The little hemispherical clear plastic dome/lens on the emitter of my Cree XR-E P4 has come off, anybody know what to use to glue it back? It seems to be some kind of sticky gel-like stuff. Many thanks for any clever ideas!

You're probably better just to toss it, and consider it a lesson learned. Good chance if you fix it- it will fail quickly.

"Fix it" by replacing it with a Q5 Cree

Yeah I think you guys might be right. Especially the Q5 idea. Thanks for the wisdom!

Lens coming off from Cree emitter occurs very commonly when too much heat is being generated during soldering, wave soldering or heating the star in order to remove the emitter. The silicon glue which holds the lens onto the metal reflector changes in property due to high heat and becomes gel like compound.

You can still power up the Cree without lens , but the beam output is yellowish in color ( sometimes having yellowish light have advantages, seems to throw a bit further than white light). You can use a tooth pick carefully remove the sticky silicon residue around the metal reflector but do not touch the yellowish emitter or else the Cree is destroyed!

If you want to re-attached the Lens back, remove the sticky silicon residue,
apply a thin coat of clear nail polish only around the metal reflector , pop the lens back and wait for a while for dry up.

richdsu said:

...If you want to re-attached the Lens back, remove the sticky silicon residue, apply a thin coat of clear nail polish only around the metal reflector , pop the lens back and wait for a while for dry up.

Click to expand...

Welcome to CPF richdsu, and you too racoon. Thanks for the tip about using nail polish for this type of fix.

Question: If you were putting the dome back on a red LED, would you use red nail-polish?

Haha what wouldl you use for a infrared LED then Thanks for the welcome LED_Thrift.

richdsu, you say to put the nail polish only on the metal ring around the lens, does that mean the nail polish must not touch the yellow emitter?

Yes, do not mess around the yellow emitter ( phosphor element).

Cree Lens I think is made of Fused Quartz ( one of these if I can get hold of one, smash it with a hammer to verify the material), very tough and chemical resistant sits nicely on top of the metal ring ( also acts a reflector). Nail polish ( aka Nail varnish) cheap and readily available should do the job holding the lens to the ring.

Clear Nail polish is also transparent, you can use it for red, blue green, infra red....:kiss:

I also use nail polish around small screw threads and heads as a form of thread locker ( loctite) :twothumbs

This will work but if there are any air bubbles under the "lens" the beam tint will be yellow due to the mismatch in refractive index. The gel is for RI matching to get the most light out the front of the device. Air will alter this and cause light to be reflected back into the led thus illuminating the yellow phosphor from the top which shifts the color tint way towards yellow and decreases lumen output as well due to loss in internal reflections. Toss it and get a new one. I have contacted Crees engineering dept about this type of issue but no reply yet.

Thurmond

How about re-applying Clear Silicon Adhesive/Sealant ( from Dow Corning) onto the cavity, paste the Lens back....let it dry up, will the Beam Color Tint restores back to white. :thinking:

My lumiled 1w red's lens popped off too (it was with my keys in my pocket). I just put a drop of clear epoxy in there. The problem is that the way i mixed it i got lots of bubbles so its not perfect. I was able to glue on a (moded) optic on too. it is still functional (tail light).

Today I go to a hardware shop and get a small tube of Clear Silicone Sealant.

I have earlier removed the gel inside my Q5 Cree Emitter ( Lens pop out problem) which was modded onto a Ultrafire C2 HaIII Flashlight ,carefully under a magnifying glass using a large needle, work around the sides,so as not the touch the phosphor area.

Next I use a penknife blade to apply the clear silicone sealant onto the Q5.
Plug the cavity ( not air voids) and scrape off any excess silicon. Place the Lens back and clean up with IPA ( Alcohol).

Viola !!! The Emitter powers up and the Beam Color is """White""" tint and clear throughout ( as good as new).

Tritium is right, the silicone layer inside the emitter pull the light off from the phosphor layer, prevent the phosphor layer from generating yellowish tint.

:twothumbs

richdsu, do you mean the kind of silicone sealant used to seal around bathtubs? Do you apply it in direct contact with the yellow emitter?

Many thanks richdsu. You're from Singapore? So am I! :wave: But I'm living in London at the moment.