Different type of Lamps used in Projectors
The different types of projector lamps used in projectors are:
- Metal Halide lamps which include HID lamps or High-intensity discharge lamps and UHP Lamps or Ultra-High-Performance lamps
- LED Lamps are long lasting projector bulbs
- Hybrid Projectors: A combination of LED and Lasers
The light intensity of projectors are specified in Lumens. So before explaining about the different types of lamps or bulbs used in projectors, we should have a an idea of what a 'Lumen' is:
What is projector Lumen
A 'Lumen' is a measure of the light out put of the projector lamp and measures how much light the projector Lamp is capable of producing. So the Lumen specification of a projector is an indication of how bright the projector is. A good way to understand Lumens is to think of light as water, then a Lumen of light would be similar to the measure of water flow in Liters per second, for example the flow of water in Liters per second from a water tap. The higher the Lumen rating of a projector, the brighter the projector should be. But there is a catch here, you should also look at the color light output of the projector, as explained in the section on DLP projectors below.
What is a Metal Halide Lamp used in Projectors
The most common type of lamps or bulbs used in projectors are the Metal Halide lamps. A metal halide lamp for projectors is also know as HID or High Intensity Discharge Lamp or UHP Lamps or Ultra-High-Pressure lamps. Metal Halide Lamps work with with an electric arc inside a high pressure glass bulb containing a mixture of Mercury vapour and a metal halide vapour, usually Sodium Iodide. Metal Halide lamps are very efficient, producing an high intensity white light of about 75 - 100 Lumens per watt.
The rated lifetime of normal Metal Halide projector lamps is 3000 hours. Projector Lamp lifetime is rated by what is known as 'Half-Life', that is the life time of the projector lamp till the lamp brightness becomes half as bright as it was when it was new.
The replacement costs of projector lamps have come down quite a bit in recent days with the advent of the online retailers like Amazon.Com who sell both generic and OEM branded projector lamps. Projector Metal Halide replacement lamps are available from about $50- to $200-. Have a look at the Projector replacement lamps on Amazon.com US website to get an idea of the costs in USA
This is the link to the Amazon India website page showing a wide range of Projector replacement lamps.
Metal Halide Lamps in projectors get very hot and it requires a high speed fan to cool it down while running. In projectors which are not well designed, there may be an audible fan noise which may disturb some. Also on starting, Metal Halide Projector lamps requires about a minute to reach its full brightness and on shutting down will require a cooling off period of about a minute before finally shutting down.
One problem using Metal Halide Lamp Projectors is that in the event of a power failure while the projector is running, causes the projector to shut down without the cooling fan being able to cool down the hot projector lamp. This will cause the Projector lamp to over heat and will shorten its life and may be even cause the projector lamp to burn out, in which case you will need a new replacement lamp. To avoid this it is recommended to fit a small UPS usually costing less than $100-, between the projector and the power supply. This will give you sufficient time, on hearing the power failure alarm from the UPS, to enable you to shut down the projector and allow the auto cooling cycle to work.
All types of projectors use Metal Halide lamps including the LCD, DLP and LCoS projectors. It should be noted here that single chip DLP projectors, with only one DLP chip to process the 3 colors of the RGB spectrum derived from the Color Wheel, can only use ⅓rd of the white light lumens of the metal halide lamps. This is explained more fully in our page on DLP Projectors.
To give an example, say the light out put from the Lamp of a single chip DLP projector is 3000 Lumens White light, then the out put in RGB Color Lumens will only be 1000 Lumens. Thus when considering the brightness or Lumens of a projector, both the white light and the RGB colored light Lumens should be considered. Projectors which have 3 chips to process each color individually and simultaneously are much more efficient and utilise 100% of the Lumen output of the Projector Lamp. Thus projectors with 3 LCD or 3 DLP or 3 LCoS chips are much more efficient than a single Chip Projector.
LED Projectors explained
LED projectors utilise LED bulbs in Red, Green and Blue RGB colors and so do not have to split white light into its individual colors. This saves a lot of space in the projector body and thus LED projectors can be made much smaller and lighter. Also the LED projector lamps have a Half Life of over 20,000 hours, some even claiming 60,000 hours. LED bulbs being solid state devices, makes LED projectors much sturdier than projectors with metal halide lamps.
LED single chip DLP projectors does not need a color wheel to produce RGB light but use color LED beams directly from the color LED Lamps to shine directly on the single DLP DMD chip.
Other advantages of Projectors with LED lamps are that they are quick to start and stop the projector. There is no need of a cooling period for an LED projector before shut down.
Another major advantage of LED projector lamps is that the brightness of the individual color LED lamps can be controlled independently. This makes it possible, say for example in a scene where no Red color is required, to dim the output of only the Red color LED bulbs, either by dimming the bulb itself or by the use of fast response Irises. This can lead to higher contrast ratios with much better quality picture on the screen.
The disadvantages of LED projectors are that they are not as bright as the Metal Halide lamp projectors. This will require that LED projectors are used in darkened rooms. Also LED projectors are more expensive than equivalent Metal Halide Projectors.
Laser Home Cinema Projectors
LASER is the short form of “Light Amplification by Stimulated Emission of Radiation”. To explain what a LASER is in simple language, we can say it is a device that amplifies Light and focuses it into a narrow beam of parallel rays of light. The light in LASERs are of the same wave length or same color, and do not interfere with each other which makes the parallel beam of a LASER able to travel very far without losing its strength. This is what makes LASER pointers possible. Other common usage of LASERs is in the Red Lasers used to read Barcodes and the Violet Lasers used in Blu-ray players. More powerful LASERS are used in industry that can cut through metal, but such powerful lasers are not used in projectors.
Laser projectors have very good pictures with high contrast ratios and the Laser lamp life in projectors is in the range of 30,000 hours plus. Lamps in Laser projectors do not produce that much heat and hence there is no need of a cooling cycle before the projector is shut down. Laser Projectors are very robustly built and reliable. The main problem with Laser projectors is that it is very expensive. But recently Epson introduced the first Laser projectors costing less than $10,000-, the Epson models LS10000 costing about $8000- and the Epson model LS9600 costing about $6000. These projectors are described in detail on our page on Laser Projectors.
The new Epson LS-series Laser projectors has two blue color Laser Lamps as the light source. One Blue laser beam is used as the Blue Light source and the other Blue Laser beam passes through a Yellow Phosphor Wheel to produce Yellow color light beam which is split into its component primary colors Red and Green.
Hybrid Projectors using led and laser
Hybrid Projectors use two types of lamps for its light source, most often LED and Laser Light sources. In the Laser-LED Hybrid Projector, a blue Laser is passed through a Phosphor element to produce the Green color light beam. Red and Blue color beams are provided by high power Red and Blue LEDs. The Light processing Chips can be either DLP or LCD, but a single DLP chip is usually made use of.
Benefit of Hybrid Projectors are that it is not as expensive as full Laser Projectors but brightness of an Hybrid Projector is boosted with power of a Laser generated Green color. Green color LEDs are not as bright as the Red and Blue LEDs, so with the green color being provided from a Laser source, makes the hybrid Projector quite bright.