This invention generally relates to projection displays, and more specifically applies to dimming in projection displays.
Various types of optical displays are commonly used in a wide variety of applications. Included among these various types of displays are projection displays. Projection displays typically involve optical relaying of the displayed image prior to viewing. A typical projection display system will often include a diffuse viewing screen. One of the attractive characteristics of many projection displays is the flexibility of configuring a system with the particular features needed for a specific application.
One important performance parameter in certain projection displays is the range of luminance that can be provided by a projection display, commonly referred to as the dimming range. In many applications it is critical that a display make information clearly visible in a wide variety of ambient light conditions. For example, a display used in an avionics control system will need to display information to the pilot under lighting conditions that can range from near total blackness to the extreme glare created by facing directly into daytime sunlight. Such a display must have a high maximum dimming ratio, where the dimming ratio is the ratio of the display luminance at highest brightness to the display luminance at its current setting. Without a sufficiently high maximum dimming ratio, a viewer of the display may be unable to easily read information from the display in high ambient light conditions, low ambient light conditions, or both. In some applications, the required maximum dimming ratio may be as little as 100:1. In other applications, a maximum dimming ratio of 20,000:1 or greater may be required to effectively display information in its expected range of ambient conditions. It should also be noted that in some applications alternative measures of light output may be used rather than luminance. In these cases, the dimming ratio can be expressed with respect to that measure. One such example might be the amount of optical power within a certain wavelength band.
Additionally, in some applications the ability to precisely control the amount of dimming is of particular importance. This is typically of greatest concern in low light conditions, where small changes in the amount of dimming can have significant effects on the viewability of the display. Unfortunately, many prior dimming solutions have been unable to provide the precise dimming control needed for many critical applications.
Thus, in many applications the projection display must be able to accurately and clearly display information through a wide dimming range, with the ability to precisely control the amount of dimming. Unfortunately, prior art solutions to dimming in projection displays have met with limited success. As mentioned above, some prior art solutions have been unable to reliably achieve the wide dimming range or the precise dimming control needed for certain critical applications. Other prior art solutions have required excessively complex structures that require large amounts of space and suffered from high cost and low reliability. Some prior art solutions have also negatively impacted the high bright state luminance required for bright ambient conditions.
Thus, what is needed is an improved dimming system that provides a wide dimming range and precise control over the amount of dimming in a projection display.
The present invention provides a dimming system that facilitates a wide dimming range and precise control of the dimming range. In one embodiment, the dimming system comprises a multi-aperture dimming system. The multi-aperture dimming system can be implemented in any display that utilizes a fly""s eye lens array. The multi-aperture dimming system comprises a plurality of moveable attenuators. The moveable attenuators are configured to form a plurality of apertures that can be controllably opened and closed. Each of the plurality of apertures attenuates a portion of the light propagating through at least one of the lenses in the fly""s eye lens array. Thus, by selectively controlling the plurality of moveable attenuators, the dimming system can control the throughput of light propagating through the fly""s eye lens array, where the throughput is the percentage of light passed compared to the light passed at maximum brightness and thus is the reciprocal of the dimming ratio at a given setting.
The moveable attenuators are preferably configured to allow substantially all light transmission through each lens in the fly""s eye lens array when the moveable attenuators are moved to open the plurality of apertures. Likewise, the plurality of moveable attenuators are preferably configured to block substantially all light through each lens in the fly""s eye lens array when moved to close the plurality of apertures. Thus, the dimming system can provide a wide range of throughputs and dimming ratios.
In a further variation on this embodiment, the moveable attenuators each have an attenuation profile at the area forming each of the plurality of apertures to increase the control over the dimming system at low light transmission levels The attenuation profile increases the dimming control by increasing the ratio of moveable attenuator movement to the corresponding change in throughput at low light transmission levels where the apertures are small and the dimming ratio is high This improves dimming control by making throughput change less sensitive to attenuator movement at these low light levels. In addition, the attenuation profile can be implemented to provide a plurality of sequential dimming modes, where each dimming mode provides a different ratio of attenuator movement to throughput change.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.