Advantages of LED Illumination for rear projection Control room Video Walls

This article analyses the advantages of Light Emitting Diode (LED) illumination systems for rear projection video walls especially in control rooms over the commonly used High Intensity Discharge (HID) Lamp with a rear projection Digital projector.

A video wall is a huge rear projection system which is primarily used in a control room. The display unit is in the form of a cube (50″ Diagonal to 100″ Diagonal – common sizes) and multiple such cubes display critical information. Each cube can display information independently or multiple cubes – 2 cubes or 2×2 cubes can join together and display the same information in a bigger view. So, you need a projection system with a good contrast, brightness, uniformity and colour reproduction. Digital projectors with their DLP rear projection technology (with High Intensity Discharge Lamps as the source of illumination) are being used currently for such display units, quite successfully. But LED – Light Emitting Diodes might as well replace them in the future because of the following advantages:

¤ The life of an HID lamp is typically less than 10,000 hours(some times much lesser) but the life of LED’s are around 50,000 to 80,000 hours. This directly translates into cost benefits as the operational cost becomes much lesser for a LED source.

¤ Since LED’s don’t contain toxic substances like mercury (Which is the case with HID lamps using mercury vapour lamps), their disposal is easier.

¤ Since LED’s don’t emit UV rays like HID lamps, they don’t affect the optical coating based on organic compounds, which are found inside the projection system – especially LCD and LCOS projectors.

¤ The use of LED’s eliminate the colour wheel (required for DLP projectors) to display colours, as the primary colours are cycled electronically, switching them on and off when required. So, one possible point of failure due to the moving parts is eliminated in LED’s.

¤ Any illumination source would lose the brightness as they age. While LED’s lose around 20% in some of the primary colours after 20,000 hours, HID light sources lose about 50% of its brightness within a few hundred hours.

¤ The brightness is also maintained more uniformly across the whole image in the video wall for LED’s which is not the case with HID lamps.

¤ As LED projectors use separate blue, green and red LED’s, allowing independent control of each of their intensities, any colour imbalances can be corrected more easily in real time.

¤ LED’s can reproduce from a larger gamut of colours, meaning it can display more shades of any colour and hence the real object colour is more accurately reproduced.

¤ The speed of a colour wheel, in a projector that uses a HID lamp is limited, meaning the number of times that the RGB colours can be cycled every frame is also limited. This may sometimes result in a rainbow effect – a white on a black image can break up into multiple colour traits. This problem is eliminated in a LED based system as the switching of colours happens at a much higher speed.

But there are also some limitations of the LED illumination systems like its spectral characteristics being dependant on the electric current driving the device and their dependence on the device’s junction temperature, which causes a few issues. But since the advantages are huge, and LED technology is improving day by day, will LED replace HID lamps in future? We will have to wait and see.

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