Basically I am going with the plan below:



the tempered glass seems to be touching the 220mm Fresnel lens.

2 questions:

1. Is the tempered glass a must?
2. If it is, how far away should it be from the lens?

-Thanks and sorry for the 2 posts.

You do need some sort of UV blocking material. Most people use Lexan (around $10 at Home Depot.) I use Lexan but am probably going to get a sheet of glass with UV coating instead because all the Lexan I get seems to be scratched up. As far as where to put it, my Lexan is right against my rear fresnel, they are in the same sled and pretty much touch each other. I think that's how most people do it.

jonjandran doesn't use a UV filter in his 1080p pro build

There is some debate about the necessity of UV filtering. I choose to go with it because I'd rather be safe than sorry.

The original LL design called for tempred glass, which is still a safety issue. The tempered glass is there for a few reasons:

1. Safety. Tempered glass keeps the lenses safe in the event that the lamp shatters. MH lamps can do this, so it's just a good idea to protect the rest of the projector in this case. (Actually, the lamp can be more accurately described as 'exploding' when it fails in this manner!)

2. Filtering. Typically there would also be a UV filter. This was commongly sandwiched in between the tempered glass and the collimator fresnel. Having them touching like this also forced the collimator fresnel to stay flat. It could be argued that it also reduced the number of surfaces the light had to pass through, if the parts were pressed together well enough, but this might be pushing it.

3. Heat shielding. Glass is actually a fairly good insulator, so the tempered glass wouild prevent the acryllic fresnels from getting too hot. Acryllic gets soft at about 100 deg C, so it is imperitive that the lenses be kept cooler than this. The LCD has to be kept even cooler, as the are typically rated with operating temperatures only up to 40 deg C or so.

Lexan can also take care of all these needs. Lexan is polycarbonate, so it can withstand much higher temperatures. (Plexiglass is acryllic, and will NOT handle the high temperatures!) It can withstand damage from the lamp exploding if this happens, the XL10 variant has UV shielding built-in and the Lexan has adequate insulative value. Still, it is no longer common practice to have the Lexan right next to the fresnel, for a few reasons. One is that the Lexan will bend too, so it is no longer useful to prevent the fresnel from bending. Two is that Lexan's physical insulating properties are not as good, so it's better to have an air gap bewteen it and the fresnel, in order to keep the fresnel cooler.

Somehow I call Home Depot and they don't know what Lexan is. I think they carry plexiglas, but this thing is much weaker and probably not as clear as glass. Do someone know if there's another name for Lexan that the Home Depot staffs may know? I plan to use a flat bed scanner's glass for this purpose as some people suggested. I know that Home Depot cut glass. However, do they cut my glass for some money or they only cut glass that they sell? If I have to go somewhere else, probably glass shop right? How much usually do they charge to cut this? By the way, does anyone know any "con" for using a flat bed scanner's glass? Thanks.

The flat bed scanner's glass is probably not tempered glass. I would recommend that you choose tempered glass or lexan. Regular glass will be prone to cracking from thermal stress and will provide little or no protection should the lamp explode.

The generic name for Lexan is polycarbonate. Home Depot should carry the Lexan brand name though, it's usually in the same area as the screen doors and windows.

But does not polycarbonate block more light that normal tempered glass? I mean, it is more like plastic than glass.
However temperature resistence is quite good - -40°C to +120°C.

Definately home depot has the lexan,, it is by screendoors and other plexiglass and it is in different sizes ,mine was perfect for my build at 10 bucks cut to size . the lexan will be marked on the sheet ..