Heat

From Lumenlab

When electrical energy is applied to the projector only a very small amount of this energy actually makes it to the screen. Most of the energy is converted into heat and needs to be removed. The key to its removal is to understand how the heat moves.

The Three Methods of Heat Transfer:

Conduction: Heat transferred via direct contact.

Convection: Heat transferred via moving air particles

Radiation: Heat transferred via Infrared light.

It is also helpful to understand that these three methods of heat movement are a generalisation. While it may seem like convection is the only method taking place, the hot air particles will also be radiating their own infrared light and conducting their heat to other air particles or materials that they come in contact with. The same can be said for conduction. An object that is hot will be radiating infrared light and conducting heat to the surrounding air particles to be convected. Infrared light will be colliding with air particles or solid objects which inturn will be convected or conducted.

The Fan:

It is only possible to remove the heat from the projector by removing the hot air particles using a fan (Forced Convection). So how does the conducted heat or infrared radiation get removed? The answer is that heat that is being conducted needs to heat the surrounding air particles before it will cool down and infrared radiation first has to collide with an object and then that object needs to conduct its heat to the surrounding air particles.

Black Paint:

By painting inside the projector black we can increase the amount of infrared radiation absorbed. If the surface is not black then the heat will simply be reflected somewhere else. It is better to deal with it in the first place of contact otherwise it could end up heating the LCD which is very heat sensitive.

Shielding:

For components that are close to the arc such as the ballast or the inside walls of the projector, they can be physically shielded from the infrared radiation so that the shield gets hot instead of the components. Then the shield can conduct its heat to the surrounding air.

Spacing the Shielding:

The shielding should not be placed in direct contact with the component it is trying to protect. There should be an air space to allow for convected heat to be removed. By placing the shielding in direct contact, it will simply conduct its heat though to the component and defeat its purpose.

The LCD:

The LCD is very inefficient at passing visible and infrared radiation. The LCD absorbs any light that doesn’t get used in the image so it needs some special attention. Obviously a black shield can’t be used but there are two ways heat can be removed. By passing cool air over the LCD it can be cooled but it requires a large amount of air which means more noise. By using special filters infrared can be removed before it can heat the LCD. This is a much better approach but the cost of ["Dichroic"] or heat-absorbing filters can be high.

The goal is to contain heat as close to its source as possible. .