My projector is almost finished but i have another question.. the inside of the box.. my box is made of wood (mdf) and i was thinking.. i have to paint it all black inside? or i have to paint black between the 2nd fresnel and the lens, and put aluminum between the light and the 1st fresnel? What should i do?
Thanks once again
Thanks once again
Painting the box keeps stray light to a minimum.
Between the LCD and projection lens, it's possible for stray light to be projected onto the screen. Obviously this is bad.
Behind the LCD, where the lamp is, stray light isn't wanted either. Many people speak of the rear fresnel lens "rejecting" light which is not from the point source. This simply isn't true. Lenses don't by nature "reject" light, they refract it. Light from the point source is refracted in a desirable way, becoming collimated through the LCD. Stray light is refracted at odd angles, passing through the LCD at an angle, creating more stray light at best.
In addition, light bouncing around inside the projector tends to become light leaks, which are undesirable.
It is possible to build your projector without painting the interior at all, or even painting it white.
Painting the inside flat black is an easy way to ensure the best possible image quality.
Between the LCD and projection lens, it's possible for stray light to be projected onto the screen. Obviously this is bad.
Behind the LCD, where the lamp is, stray light isn't wanted either. Many people speak of the rear fresnel lens "rejecting" light which is not from the point source. This simply isn't true. Lenses don't by nature "reject" light, they refract it. Light from the point source is refracted in a desirable way, becoming collimated through the LCD. Stray light is refracted at odd angles, passing through the LCD at an angle, creating more stray light at best.
In addition, light bouncing around inside the projector tends to become light leaks, which are undesirable.
It is possible to build your projector without painting the interior at all, or even painting it white.
Painting the inside flat black is an easy way to ensure the best possible image quality.
thanks for your explanation SupraGuy.
i'll paint the insid eall black then. i just don't know if it will be worth put aluminum between the rear fresnel and the light source to protect my box to burn
Theres any story of some one that built a box in wood and the box becames so hot that burn? i'm a bit afraid about that.
i'm using a HQI-T 150w and i have a fan pointed direct to the lamp positioned behind it (because the hot air should goes up.. just like balloons, right?) and on the top over the lamp an open grill. and then on the side another fan to help even more to push the air to outside the box.. i just don't know if it will be enough
meico about that paint that you talked about i went to a local store and the info i got is that the paint is for metal and in wood it wont have the desired effect... i don't know if it's true or not.. it wsa just the info that i got
i'll paint the insid eall black then. i just don't know if it will be worth put aluminum between the rear fresnel and the light source to protect my box to burn
Theres any story of some one that built a box in wood and the box becames so hot that burn? i'm a bit afraid about that.
i'm using a HQI-T 150w and i have a fan pointed direct to the lamp positioned behind it (because the hot air should goes up.. just like balloons, right?) and on the top over the lamp an open grill. and then on the side another fan to help even more to push the air to outside the box.. i just don't know if it will be enough
meico about that paint that you talked about i went to a local store and the info i got is that the paint is for metal and in wood it wont have the desired effect... i don't know if it's true or not.. it wsa just the info that i got
aluminum against wood = fire
I have read on another forum about aluminum sheet metal directly against wood. Where this was close to the lamp, it burned the wood under the metal.
It is a good idea to have aluminum between the lamp and any wood surface that will be near. But you need to have some circulating air space between the aluminum and the wood. That lets the heat transfer out of the aluminum and into the air so it can be removed from the box.
I have read on another forum about aluminum sheet metal directly against wood. Where this was close to the lamp, it burned the wood under the metal.
It is a good idea to have aluminum between the lamp and any wood surface that will be near. But you need to have some circulating air space between the aluminum and the wood. That lets the heat transfer out of the aluminum and into the air so it can be removed from the box.
add spacers under the aluminum
Just cut it a bit smaller. Then you can add some 1 cm spacers underneath the aluminum, so it does not all rest against the wood. Leave a 1 cm gap at each edge of the aluminum, so air can go behind it.
Or a different approach:
If you put the lamp inside a metal box, then you don't need any more aluminum any place that is not directly exposed to the lamp. It is also useful to enclose the lamp, because then you can have a fan push or pull cooling air across the surface of the lamp and direct the hot air out of the projector.
In my projector, the lamp is enclosed on four sides by a 15 cm by 15 cm by 10 cm high aluminum box. There is a fan mounted at the side of the projector with a metal duct that is attached to one end of the lamp box. The fan pulls air across the surface of the lamp and pushes it out of the projector, so the inside of the projector stays very cool. The light passes through a 100 cm diameter hole in the top of the lamp box, where I have a hot mirror installed. In the picture below, I have removed the front piece of the duct for the photograph so you can see the lamp and reflector. You can also see the 1 cm spacers under the aluminum plate to keep it from burning the wood.
Just cut it a bit smaller. Then you can add some 1 cm spacers underneath the aluminum, so it does not all rest against the wood. Leave a 1 cm gap at each edge of the aluminum, so air can go behind it.
Or a different approach:
If you put the lamp inside a metal box, then you don't need any more aluminum any place that is not directly exposed to the lamp. It is also useful to enclose the lamp, because then you can have a fan push or pull cooling air across the surface of the lamp and direct the hot air out of the projector.
In my projector, the lamp is enclosed on four sides by a 15 cm by 15 cm by 10 cm high aluminum box. There is a fan mounted at the side of the projector with a metal duct that is attached to one end of the lamp box. The fan pulls air across the surface of the lamp and pushes it out of the projector, so the inside of the projector stays very cool. The light passes through a 100 cm diameter hole in the top of the lamp box, where I have a hot mirror installed. In the picture below, I have removed the front piece of the duct for the photograph so you can see the lamp and reflector. You can also see the 1 cm spacers under the aluminum plate to keep it from burning the wood.
Attachments
i have my project this way:
the hole that you see on the right has one fan pushing air outsite and at the moment i have another hole just under the lamp where i have another fan direct to the lamp. than on the top another hole (without any fan) to let the air pushed from the fan under the lamp put the air outside...
Thats what i have at the moment..
An externally hosted image should be here but it was not working when we last tested it.
the hole that you see on the right has one fan pushing air outsite and at the moment i have another hole just under the lamp where i have another fan direct to the lamp. than on the top another hole (without any fan) to let the air pushed from the fan under the lamp put the air outside...
Thats what i have at the moment..
I think it will burn!
I think the exposed edge of the controller board will be burned by the lamp. Also the wood parts that are close to the lamp will burn. If you put metal directly on those wood parts, the wood will insulate the metal so it does not lose any heat. As the energy from the lamp heats up the metal, if will soon get hot enough to burn the wood underneath.
I suggest you redesign it so the lamp is mostly surrounded by an aluminum box that is not in direct contact with wood. Cooling air should be moving on both sides of the box metal. The energy will be transferred into the cooling air instead of heating up the metal too much.
I think the exposed edge of the controller board will be burned by the lamp. Also the wood parts that are close to the lamp will burn. If you put metal directly on those wood parts, the wood will insulate the metal so it does not lose any heat. As the energy from the lamp heats up the metal, if will soon get hot enough to burn the wood underneath.
I suggest you redesign it so the lamp is mostly surrounded by an aluminum box that is not in direct contact with wood. Cooling air should be moving on both sides of the box metal. The energy will be transferred into the cooling air instead of heating up the metal too much.
distance, shielding, air flow
All of these will prevent overheating wood parts near your lamp. But a piece of exposed wood just a few inches from a MH lamp will get hot enough to burn.
Just attaching a piece of aluminum to that wood will not help: Shiny aluminum does not radiate heat very well, so it just gets hotter and hotter if it is insulated by wood right behind it.
There are several solutions: A simple one is to build a large box so the lamp is several inches from any of the exposed wood. Another is to enclose the lamp mostly in a metal box with forced air cooling so the non-lit side of the metal will not emit much heat.
As for painting, I would say paint everything flat black that is not supposed to reflect or transmit light. I also use black felt in the upper half (the cool part) of my projector. It's very nice for sealing light leaks around projection lenses, cutting out reflections back to the LCD surface, etc. Stray reflections really kill your chance for a clean image.
All of these will prevent overheating wood parts near your lamp. But a piece of exposed wood just a few inches from a MH lamp will get hot enough to burn.
Just attaching a piece of aluminum to that wood will not help: Shiny aluminum does not radiate heat very well, so it just gets hotter and hotter if it is insulated by wood right behind it.
There are several solutions: A simple one is to build a large box so the lamp is several inches from any of the exposed wood. Another is to enclose the lamp mostly in a metal box with forced air cooling so the non-lit side of the metal will not emit much heat.
As for painting, I would say paint everything flat black that is not supposed to reflect or transmit light. I also use black felt in the upper half (the cool part) of my projector. It's very nice for sealing light leaks around projection lenses, cutting out reflections back to the LCD surface, etc. Stray reflections really kill your chance for a clean image.
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