Lamp vs solid-state light sources in projectors

Almost 400 years have passed since Christiaan Huygens invented the first “Magic Lantern” projector. Before the invention of electricity, projectors used a kerosene lamp as a light source. Therefore, the design of the first projectors was similar to a kerosene lamp.

Of course, modern projectors are radically different from their prototypes. As known, its brightness directly affects the quality of the projection. Therefore, lamp improvement has become one of the main directions in the process of improving projectors. Basically, their evolution ended in 1995 when Philips developed the high pressure mercury UHP (ultra high performance) lamp.

Today lamp projectors use modern UHP lamp modifications.

Introduction

At the turn of the century, the semiconductor industry was able to provide relatively cheap and powerful LEDs. Their miniature size and work without overheating have become a huge plus compared to lamps and projector developers haven’t missed new opportunities. As a result, companies have developed a huge number of LEDs models, including the very popular ultraportable mini projectors.

The addition of an optical cavity to the LED ushered in the era of miniature laser LEDs.

They have become an ideal light source in mini projectors because of the perfect focusing of coherent radiation. Of course, laser LEDs also have disadvantages, including laser speckle and high cost. However, even phone makers did not resist the temptation and developed several smartphones with a built-in laser projector. Today comparison phone projectors vs phone +projector is not in their favor, but projector smartphones have good promise.

Usually, innovations quickly displace models of previous generations from the market. But lamps, LEDs and laser projectors continue to compete successfully with each other, occupying a certain niche. For example, many industry leaders, including BenQ, Acer, Epson, etc continue to use lamps as a light source in Home Theater projectors.

Modern projector with solid-state light sources

Modern models use LEDs, laser LEDs, or a combination of both. This is due to the following factor. Green LEDs are not bright enough. Green laser LEDs are very expensive. To solve this problem, Casio engineers developed a hybrid projector that uses LEDs and laser LEDs at the same time. The hybrid projector uses reasonably powerful red and blue LEDs, and a relatively cheap blue laser instead of an expensive green laser. The blue laser provides the formation of a green color with the help of phosphor wheel.

Today DLP and 3LCD technologies use this elegant idea, generating colors from the beam of a blue laser diode and a phosphor wheel. This solution has allowed companies to significantly reduce the cost of solid state projectors.

Lamp vs solid-state light sources

A list of the main differences between lamp projectors and models with solid-state light source includes:

– brightness range;

– lifetime and degradation rate;

– price and design features.

Brightness range

The brightness range of modern lamp projectors varies from 1,000 lm to over 4,000 lm. LED projectors provide brightness from several tens lumens to 4,500 lm. The brightness range of laser projectors is much wider. It’s only 30 lumens in budget pocket models, and reaches 75,000 lumens in expensive installation models.

Today the list of the most powerful models is topped by the Barco XDL-4K75 4K, 3-chip DLP RGB laser projector with 75,000 lumens brightness and a price of about $ 380,000.00 (€ 325,000.00).

Its dimensions and weigh reach 29.3 x 56.9 x 27.8 inches (71 cm x 74 cm x 145 cm) / chillers: 27.6 x 27.6 x 31.5 inches (70 cm x 70 cm x 80 cm), and 520lb (~235kg) / chillers: ~250lb (~115kg) per chiller (two chillers needed).

Lifetime

Lamp life varies depending on projector model and operating mode. It typically is 2,000-3,000 hours at full power. Eco mode increases it to 5,000 – 6,000 hours.

The replacement cost depends significantly on the lamp power and can vary from several tens to several hundred US dollars.

Nearly all modern lasers and laser LEDs run 20,000 hours or more at full power, and up to 30,000 hours in Eco Mode.

In addition, lamps and solid state light sources lose brightness at different rates. For example, the lamp brightness decreases by about 25% in the first 500 hours of use. Then it gradually decreases to 50%. After that, manufacturers recommend a replacement. Therefore, Lamp life in specs is calculated to reduce power by 50%.

Of course, companies are trying to increase Lamp life, which, basically, depends on the starting current. In turn, it depends on the cathode resistance, which increases due to pollution. As a result, engineers have developed a smooth shutdown mode. Preheating the cathode prior to shutdown increases the cooling time and reduces fouling from combustible microparticles. This technology significantly increases Lamp life and is used, for example, in Sharp projectors.

Projector owner can easily check his model. Without this mode, the screen immediately turns black after shutdown. Smooth mode lengthens the blackout time to 20-30 seconds.

The brightness of solid-state projectors decreases significantly more slowly. Panasonic’s test results showed only a 10% decrease in laser brightness after 1,000 hours of use, which equates to approximately 6 months of normal use. After 6,000 hours of operation, the laser projector delivered 85% of its original brightness.

Price and design features

Of course, the low price is one of the main advantages of the lamp models. But the need to replace it significantly affects this factor.

On the other hand, fierce competition is driving the rapid pace of improvement in modern consumer electronics. Of course, projectors are no exception. This list includes continuous improvement in connectivity, increasing resolution, improving HDR quality, smart functions extension, etc. As a result, the model becomes hopelessly outdated after just a few years. Given this factor, a short lamp life is not very important with infrequent use.

Therefore, powerful and relatively cheap lamp Home Theater projectors remain competitive.
For example, according to many experts, BenQ HT2050A remains one of the best home theater projectors at $ 700.

Replacing it 240W metal halide bulb costs about $ 80. Moreover, lamp BenQ HT3050 and HT2050 are also very popular.

But daily use of the projector as a TV for five hours or more can significantly increase the total cost of ownership due to lamp replacement. In this case, its brightness will decrease by about 25% after just three months. Therefore, models with solid-state light sources are more profitable with intensive use.

The difference in size and noise is due to the lamp heating during operation. Of course, a powerful lamp requires intense and efficient cooling. Therefore, lamp models often use a sufficiently large and powerful fan, which, in turn, requires an increase in the internal volume. In addition, the audible noise of some budget high-power projectors reaches 50 dB, reducing viewing comfort.

Conclusion

The pros of solid-state projectors:

– instant on / off;

– long lifetime of solid-state light sources;

– wide color gamut and constant brightness with high uniformity of white;

– does not heat up;

– very slow degradation of solid-state light sources;

– low power consumption.

Energy efficiency is due to the narrow spectrum of laser LEDs, which provide brightness by generating only certain frequencies (wavelengths of red, green and blue colors). Accordingly, the rest of the frequency spectrum does not require generation energy.

Today these projectors dominate the ultraportable pocket projectors segment and as premium projectors for Home Theaters. In addition, DLP 3 Chip laser projectors can operate 24/7/365 in any orientation 360 degrees on all axes. The ability to work around the clock without maintenance opens up additional opportunities for laser projectors, including installations, outdoor advertising, etc.

Lamp projectors are great for budget Home Theaters, providing high quality big screen movie viewing. Of course, LED models are also present in this segment. But they are more expensive compared to lamp projectors with similar specs.

This video offers comparison of lamps, LEDs and laser LEDs as light sources for projectors.