Monday, February 25, 2019

Projector lamp or light-source tech evolution - 4 main types

Projectors rely on the same principles of operation dating back to the prehistoric ages. For an image to be projected to a screen there has to be a built-in light source which is then focused to the screen. This projector lamp or light-source tech has evolved dramatically over the years, driven by the need to address 3 important factors - efficiency, environmental impact and lifespan of the source.  With the world moving towards a greener community, technology needs to be cheaper, more efficient and pose no environmental hazard. The projector light sources, which are discussed in this article, are classified into:

  1. Traditional lamps

  2. Pure LED

  3. Hybrid

  4. Laser

Traditional lamps are still being used to this day owing to their success in the past years, but newer technology like hybrid, or even better, pure laser technology is fast gaining ground. We now look at each of these projector light sources from the old to new, highlighting the respective features.




1. TRADITIONAL LAMP


Traditional projector lamp or light-source falls into a tech group called high-intensity discharge (HID) lamps, where
an electric arc passes through a gas (halogen or metal salts) in the bulb which heats up to produce visible light. It's amazing this technology was discovered after observing how lightning is produced. There are several types of traditional lamps used and all use this same principle of HID lamps.

Metal Halide Lamp


Lifespan : about 3000 hrs

Lumens : 75 to 100 lumens per watt (about twice that of mercury vapor lamps)

This type of lamp was developed in the late 60s. An electric arc passes through a mixture on mercury vapor and metal salts ( e.g. sodium iodide salt) to produce light. The metal halide improves efficiency of the bulb and also color rendition is better as compared to having mercury vapor only. Due to the high cost and better picture quality, this kind of bulb is used in medium to high-end projectors, where cost is sacrificed for quality.

Pros

  • Compared to UHP (see below) lamp, metal hallide lamp has better picture quality

  • Higher efficiency



Cons

  • Loses brightness over time as in other traditional lamps

  • Produces a lot of heat so a fan is needed to cool the unit

  • Need time to warm up when projector is switched on

  • Needs time to cool down after use such that turning off the fan abruptly may actually damage the bulb

  • More expensive than UHP lamp

Ultra-High Perfomance (UHP) Lamp/Pressurized mercury vapor lamp


Lifespan : 2000 to 3000 hrs

Lumens : About half that of metal halides (above) for the same wattage

This is the most common projector light source at the moment having been around for a long time and it falls under gas discharge lamps. An electric arc passes through pressurized mercury vapor to produce light. Pressure is around 200 atmospheres in the bulb. In other words, it is a form of mercury vapor lamp and was developed by Philips in 1995. Peak performance of the bulb lasts 2000 to 3000 hrs.

Pros

  • Very bright

  • Less expensive to replace

  • Uses less energy as compared to metal halide lamps for the same lumens

Cons

  • Loses colour consistency over time

  • Loses brightness over time

  • Produces a lot of heat so a fan is needed to cool the unit

  • Need time to warm up when projector is switched on

  • Needs time to cool down after use. Turning off the fan abruptly may actually damage the bulb.

Xenon arc lamp (Short-arc High Pressure Lamp)


Lifespan : 1000 to 2000 hours

Lumens : Can go beyond 30000

This is a gas discharge lamp and is used as an alternative to UHP bulb. An electric arc passes through pressurized, ionized xenon gas to produce light.

Pros

  • Produces bright white light close to natural sunlight

  • Hence better color saturation

  • Has more consistent performance as compared to other traditional lamps, hence doesn't dim over time

Cons

  • Heat still produced but less than in UHP and Metal hallides. However is still needed.

  • Needs time for warming up and cooling down

  • Very expensive and rarely used for domestic projectors but high-end projectors

  • Shorter lifespan


Storage of projector lamp or light-source tech




It's important to know the precautions to take so that the lifespan of the projector lamp or light-source tech is extended. Dust is the number one enemy of the lamp and a bad lamp ultimately produces a bad picture. Therefore it has to be in good working order to minimize maintenance costs . The precautions include:

1. A cool, dust free environment

2. Let the fan cool down the lamp unit after use as was highlighted. Mercury lamps are easily damaged if this process is not allowed

3. Ensure the vents are not blocked when the projector is operating

Although a traditional lamp or light-source is still in use, there has been a shift to solid state tech that offer huge improvements in reliability and safety. Casio was the first company to do away with traditional lamps altogether. Mercury found in HID bulbs is a hazardous substance and has to be properly handled. Fortunately the newer projector lamp or light-source tech described next eliminate this risk.



2. PURE LED (Light Emitting Diode) LIGHT SOURCE


Lifespan : can last 20000 hrs

Lumens : less than 2000

LED technology has taken over the industry and is found in almost every engineering sector, be it in cars, street lights, mobile industry to name a few. In projectors it is found mainly in small projectors (pico-projectors), where the lumens is less than 2000. They don't have much brightness so LED light is not ideal for bigger projectors which need to put out more light. Pure LED has limited use due to reduced brightness and this led to development of Hybrids.

Pros

  • Small, portable projectors can be made

  • Less energy used

  • No heat so no need for a fan and is quieter

  • Mercury free so no environmental hazard

  • Don't require warming up so fast to set up

  • No cooling down of unit after use required

  • No lamp change needed

Cons

  • Less bright as compared to hybrid



3. HYBRID LIGHT SOURCE


Lifespan : can last 20000 hours

Lumens : 1600 to 4000 lumens (similar to mercury lamps)

To make for the shortcoming of pure LED projector lamp or light-source, the hybrid light incorporates laser tech to improve the brightness. Therefore the light source comprises of:

  1. Red LED

  2. Blue laser

  3. Green laser created by bouncing a blue laser off a spinning phosphor wheel. A pure green laser is expensive to make, hence the alternative technique.

Pros 

  • Are similar to those of pure LED light source. However it performs better

  • Images are as bright as mercury lamps, but it doesn't lose brightness over time

  • Ideal for heavy use as in presentations

Cons

  • More expensive than pure LED light source due to the laser component



4. LASER LIGHT SOURCE


This technology was incorporated in projectors by Sony in 2010 and uses a highly efficient laser light source with no LED component. A red, green and blue laser combination is used. The light can deliver more than 35000 lumens, similar to xenon lamps, hence ideal for use in cinemas. The only hindrance to the technology is cost, as it is >15 times more expensive than other light  sources.

Lifespan: can last 20000 hours

Lumens : can go up to 35000


Pros

  • Are the same as in other solid state technologies described above

Cons

  • Very expensive

  • In some states you need a licence for lumens >5000 because laser light can cause tissue damage if not handled properly

CONCLUSION


Projector lamp or light-source tech has changed dramatically and currently pure laser light source is the best. If costs come down this technology will render traditional lamps obsolete. If you want to know how you select the appropriate brightness of projector image read here.

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