with a silicone-type material for the most part and not glass? Is it because it’s easier/cheaper manufacture-wise?
I’m just wondering if also maybe domes are designed to be flexible so they take vibration and shock better. Or maybe because the silicone-type material can be layered on thick enough that it covers/conforms to the emitter itself and provides some other benefit whether thermal in nature or whatever.
One could almost think that this silicone-type material wouldn’t be quite as ‘clear’ as good ol’ glass but apparenty it tiz.
You want to seal off the phosphor that converts the UV light that these LEDs actually emit (converts it into light in the visible range). This also the reason why "de-doming" often goes wrong... sometimes you rip some phosphor off the die and sometimes the remaining phosphor ages very quickly, because the phosphor reacts with the oxygen in the air.
I think it might be down to manufacturing, bose301 will know, but perhaps the silicon is deemed “good enough” and can be applied quicker in the manufacturing process as a pose to a robot gluing a glass dome then applying it to the die?
Every additional layer with a different optical index makes the overall performance worse, as some light is being reflected so the "glue" would probably make the use of glass pointless.
In that case, I go with your answer glass domes would be more expensive and would require the additional step of gluing or fastening.
For heat dispersion silicone type products aren’t the best choice for a conductor.
Glass would probably be the best, lexan type (plexiglass) will yellow with exposure to UV. (Sunlight takes less than a year )
I read somewhere that the optical grade silicone used had a higher transmission rate than almost any type of glass and that it actually costs an incredible amount for it’s weight.
Glass simply wouldn’t be practical though I don’t think, how would it attach to the die?
It depends totally on how the "operation" goes and if you break the "seal". The outcome can work very well ,or can be disastrous .... you can build a very effective UV light (or here) this way. I can't seem to find the pic of the de-domed XM-L with the brown spots anymore, where the reaction is shown to oxygen. If I find it again, I will link it here. Most of the heat is dissipated through the LED socket to the star and to the pill, so the thermal specifications of the primary optic isn't as important as one would think. Air is a very good insulator when there is little to no convection.
"White LEDs can also be made by coating near-ultraviolet (NUV) LEDs with a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, so more energy is converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin."
I know you CAN do it, but 99% are not done that way. The base LED for pretty much all white LEDs is in the 440nm-470nm range which is very much blue, not even into violet yet, let alone UV.
The German Wikipedia article on typical white LEDs claims that even a blue/white "base"-LED (before phosphor) is emitting a fraction of UV light. (also converted to get the highest efficiency and use all the energy that is available) The majority is in the visible (blue) range of course.
"White LED.....
The ultraviolet component, that blue LEDs transmit on the short-wavelength part of their radiation spectrum, is also is also largely converted to yellow light by the fluorescent layer..... "
glass domes would be more expensive and would require the additional step of gluing or fastening.