Current Situation and Application Analysis of LED Stage Lighting

LED Stage Lighting

1 Status of LED stage lighting

1.1 Overview of Technology Development

Since the emergence of blue light, white light and high-brightness LEDs in the 1990s, the luminous efficiency of LEDs has been continuously improved, and commercial LED tubes have now reached the luminous efficiency of 50 lm/W~100 lm/W, and its luminous efficiency is still with continuous improvement, it is estimated that it will eventually reach about 200 lm/W, which is not only much higher than 10 lm/W~30 lm/W incandescent lamps (including tungsten halogen lamps), but also much higher than all current light sources. However, the power of a single LED is very small, only 1 W ~ 5 W, and the luminous efficiency is only a few hundred lumens, and the stage lamps often have a power of kilowatts and a luminous flux of tens of thousands of lumens. Therefore, many people have never thought of using LEDs before stage lighting.

At the beginning of this century, blue LEDs were popularized, white LED technology gradually matured, the luminous efficiency of LEDs was doubled compared to incandescent lamps, and the lifespan of high-power (watt-level) LEDs could reach tens of thousands of hours. With the advantages of light convenience, new LED stage lamps that combine multiple LEDs to increase the total luminous flux begin to appear. At first, due to technical reasons and expensive prices, this kind of lamps was rarely used. In recent years, due to the improvement of the luminous efficiency of LED lamps and the popularization of accessories such as condenser cups, tube cores and shells, many manufacturers have begun to assemble and produce them. LED lamps have attracted people to try because of their bright color, energy saving and environmental protection.

Some performances have used LED lamps and achieved good results.

At present, there are two modes of LED for white light illumination: one is to add phosphor powder to the die that emits blue light, so that part of the blue light emitted is converted into yellow light through the phosphor powder, and part of the blue light and yellow light are mixed into white light; The other is to combine three LED tubes that emit red, green and blue light respectively, and form white light after mixing. The former method is mostly used for TV lighting, and the latter method is mainly used for stage lighting.

1.2 The advantages of LED for stage lighting

LED lamps can be used for stage lighting, thanks to its several main features:

(1) Energy saving and high efficiency.

Compared with incandescent light sources (including tungsten halogen light sources), LED lamps are very energy-efficient. We can observe this by comparing the structure of the two lamps.

a. The light effect of incandescent lamps. Among the currently commonly used incandescent spotlight lamps, the incandescent bulb as a light source is relatively large in size, and often adopts the structure of a reflector and a condenser lens. One of them is a spherical reflector. The filament is located at the center of the spherical reflector. The spherical surface reflects the light behind the lamp back to the filament and moves forward together. Converge into a nearly parallel beam. b. The light effect of halogen tungsten lamps. The current high-efficiency ellipsoid mirror imaging spotlights benefit from the miniaturization of halogen bulbs, and the filament is located at a focal point inside the ellipsoid mirror.

Due to the characteristics of the ellipsoid, it has two focal points. After the light emitted from one focus is reflected by the ellipsoid, it will focus on the other focus. The focal point of the condensing lens in front of the lamp is closed to the second focal point of the ellipsoid reflector, so that the light emitted by the light source that has been reflected and passed through the second focal point can be collected into a bundle of parallel rays. Due to the halogen filling in the bulb, the process and materials of the filament and the bulb are improved, the size of the bulb is reduced, and the bulb is deeply wrapped in the ellipsoid reflector. The ellipsoid reflector has a large inclusion angle for the bulb. Most of the light is used, and the light efficiency of the lamp is higher than that of the previous lamp, which can reach 40% to 50%.

c. The light effect of LED lamps. The current common LED beam light uses a special condensing cup, and the LED light-emitting diodes are installed in the fully transparent condensing cup. The middle of the condenser cup is a convex lens, which gathers the light beam emitted forward by the LED tube located at the focal point of the convex lens into a parallel beam, and the light beam emitted from the side of the LED tube enters the inner side of the condenser cup and then refracts to the outer side of the condenser cup. The outer side and inner side of the condenser cup are designed to have a certain angle. When the light reaches the outer side, the incident angle of the light on the outer side will be greater than the critical incident angle of the material of the condenser cup, so it is impossible to refract, only the total reflection is generated and emitted from the front. After a reasonable design, the emitted light will become a parallel light parallel to the optical axis of the lamp.

There is a high-efficiency reflector inside the high-power LED tube, which is a one-way light source.

A small condensing cup can use almost all the light emitted by the LED tube to form a parallel beam, and the utilization rate of the light source is very high. Since the light emitted by the LED tube does not contain infrared rays, the temperature of the LED is not too high. Although the concentrator cup is close to the LED, it can still be made of polyester plastic with high light transmission, and it will not be deformed by high temperature. Well-designed, press-molded condenser cups, manufactured in batches, with excellent consistency.

The LED tube and the condenser cup are combined into a module, but the luminous flux is not enough. Generally, the same modules are combined again to form a flat LED array. In this way, an LED lamp with more than 100 watts emits light. The light is equivalent to the brightness of several hundred watts of tungsten incandescent lamps, which can already meet the needs of stage applications and meet the requirements of energy saving.

Some people refer to the optical design inside the LED as the primary design, the condenser cup design as the secondary design, and the combination of the condenser cup modules as the third design. The assembly process of the flat condenser cup module is relatively simple. Since the parallel light beams emitted by each module are overlapped on the same plane, the entire lamp emits a slightly divergent parallel light beam, which emits light through a large number of LEDs to generate strong light that meets the needs of the stage.

Comparing LED lamps with incandescent lamps, on the one hand, the luminous efficiency of LED tubes is more than twice that of incandescent lamps; secondly, light-emitting diodes take advantage of their small size and low temperature to adopt a more efficient optical path design. , the utilization rate of the luminous flux of the light source is several times higher than that of incandescent stage lamps. The two factors are superimposed, the same luminous flux, the power of incandescent lamps is several times larger than that of LED lamps. Therefore, LED lamps with lower power can meet the requirements of light intensity required by the stage.

(2) The color is bright.

In stage performances, lights are used to dye stage sets, props, and costumes, or to create a specific stage atmosphere, and stage performances use a lot of colored light. Compared with the color light commonly used in stage lighting, LED lighting is better than traditional light sources in terms of color performance. In the past, the color light used in stage lighting was to add color filter paper or other color filters in front of the white light-emitting lamps, that is, to block the unwanted color light and only pass the required color light spectrum. Because a lot of unwanted color light is blocked, the emitted color light is quite weak, especially the commonly used blue light, whose spectrum is at the high end of the visible spectrum. Sensitive, a lot of light sensitive to the human eye is blocked, and the luminous efficiency of the lamp is lower.

At the same time, in order to prevent the color filter from fading at high temperature, the color filter must transmit a large amount of infrared components in the spectrum. While the blue color filter transmits short-wavelength blue light, it also transmits some long-wavelength red light. Therefore, the blue light obtained by adding a blue color filter in front of the incandescent lamp not only reduces the brightness, but also has an impure color, which is difficult to satisfy the lighting engineer.

LED lamps are on the contrary. Its red, green and blue light is emitted by three light-emitting tubes, and white light is mixed by three primary colors. When a certain color light is needed, only the unnecessary spectrum emission is reduced, and the color light of the required spectrum can be emitted. , As a result, the luminous efficiency of lamps is greatly improved. Especially the blue light, the blue light brightness of the LED light is equivalent to the brightness of the incandescent light fixture with more than ten times the power plus the blue color paper. The color light of LED lamps sometimes appears too pure and bright in actual use. In order to reduce the saturation of the color light, some LED lamps also add white LED lamp chip to produce elegant color light.

Because the luminous efficiency of LED is higher than that of incandescent lamps, the luminous efficiency of lamps is higher than that of ordinary incandescent lamps, and the efficiency of color light is much higher. LED lamps are used for stage performances to generate the required colored light, which can give full play to the advantages of LED. .

(3) Long service life.

The lifespan of LEDs is as long as tens of thousands of hours, while the lifespan of incandescent lamps is only hundreds or thousands of hours. However, in the early research and development of LED lamps, there was a difficult heat dissipation problem after the LED was installed in the lamp, which greatly shortened the life of the LED and affected the promotion of LED lamps. The LED tube is a semiconductor that emits light. At the current technological level, 10%~20% of the electrical energy input when the LED is working which converted into visible light, and the remaining 80%~90% of the electrical energy will be converted into heat energy, which must be dissipated in time, otherwise, will cause the die temperature to rise. If working at room temperature, the life of LED can reach 50,000 to 100,000 hours.

When making stage lamps, many LED tubes are concentrated together, and the temperature of the LED tubes will increase, which will reduce the luminous efficiency and shorten the life of the LED tubes.

At present, the structure of the general power LED tube has been greatly improved. It not only has a heat-conducting substrate, but also is equipped with an aluminum-based metal core printed circuit board (MCPCB) as a heat-dissipating substrate, which is convenient for the heat generated by the internal chip. In addition to the heat dissipation plate with sufficient heat dissipation area or with heat dissipation fins, the entire heat conduction channel from the LED tube body to the outside of the lamp body is also designed very scientifically. 150 ℃), the life of LED can reach tens of thousands of hours.

(4) Easy to use.

LED stage lighting is very convenient to use.

The working voltage of LED is 3 V~5 V DC. If you want to change the 220 V AC power of the LED stage lighting into a dimmable low-voltage DC power supply, you only need a lighting console that sends out DMX signals, and you do not need a general stage. A dimmer must be added to the luminaire. The brightness of the red, green and blue LED tubes is controlled by the DMX512 signal from the console, and the beams of various colors and brightness of red, orange, yellow, green, blue, blue and purple can be adjusted. One light can replace multiple conventional stage fixtures of different colors, eliminating the need for color changers. Moreover, the lamp body does not have fragile items such as glass bulbs and filaments of ordinary incandescent lamps, and handling and daily maintenance are much simpler, especially suitable for performance occasions where the stage is often disassembled.

2 The current problems of LED stage lighting

LED stage lighting has many advantages and is very advanced, but it has not yet been popularized in stage performances. The main problems are as follows:

(1) The current price is relatively high.

At present, the use of LED stage lighting is limited, and the large price gap with conventional stage lighting is an important resistance to promotion.

The high cost of LED lamps is mainly due to the following reasons: high-quality light-emitting diode dies are mainly sourced from foreign manufacturers such as the United States and Japan, which need to be imported, and the price is high; the development cost of new lamp light paths and lamp structure, and the cost of high-performance materials It is also very high; the switching power supply used to efficiently convert the commonly used 220 V AC mains into the low-voltage DC power required by the LED inside the lamp, the dimming control circuit required to adjust the color brightness of each LED in the lamp, and the control circuit with the console. The connected DMX512 signal receiving and decoding circuit, etc., not only increase the function, but also increase the cost of the lamp. LED lamps are still a high-tech product at present, and it will take time for the cost to drop significantly under the condition that they have not been applied in large quantities.

(2) The variety is relatively single.

At present, there is a single variety of LED lamps, which is mainly an optical structure: a square or circular light-emitting surface formed by multiple LEDs and condenser cups arranged in a plane to form an LED beam lamp. A large number of LED light sources are made on a plane to form a plane luminous body that shines on the object. Except for a uniform light spot in the central area, the periphery is a softly gradient aperture, forming an attenuation area from bright to dark, and it is difficult to form an edge. Clear hard spot, it is more difficult to use the image sheet to cut into various shapes of spots. Such LED lamps can be used as floodlights or light beam lights with low requirements. They should adapt to the different requirements of stage performances for light beams, such as hard spot occasions requiring clear edges, or strict requirements in the light area, and the beam needs to be imaged and cut. Difficult to apply.

Generally, stage spotlights (except PAR lights) have a beam angle size or a soft and hard adjustable range, and the above-mentioned LED beam lights cannot be realized. If it is used as a flood light, the iodine tungsten lamp and asymmetric reflector in the sky curtain cloud light commonly used in the stage can project uniform light to the sky above or below the stage canopy, and the lamps arranged in the LED module plane are all symmetrical light distribution. , Therefore, LED lamps are also lacking as skylights.

(3) The quality is uneven.

Due to the continuous speculation about the concept of “fourth generation electric light source” and “energy saving and high luminous efficiency” in recent years, the number of LED lighting manufacturers at home and abroad has increased significantly, and LED lighting products have been overwhelming.

At present, there are many domestic and foreign enterprises producing LED tube products, and the product quality and price vary greatly. There are many manufacturers that produce or imitate condenser cups, and some manufacturers do not design, but just purchase components and assemble them into lamps. Therefore, the same LED lamps and lanterns are similar in appearance, but due to the use of different production processes and components, the luminous efficiency varies greatly.

In fact, the production process of LED is very demanding, and not all companies have the corresponding strength, which causes the quality of LED lamps in the market to be uneven. The optical system design requirements of LED lamps are very precise. The size of the LED tube and the condenser cup is very small, and the relative position of the two is relatively high. If there is a small deviation, there will be a big difference in the position of the light reaching the stage. In order to meet the design requirements, manufacturers with strict process requirements will screen the consistency of a large number of LED tubes. Considering the gap between the thickness of the LED tubes on the circuit board, the manufacturers will adopt an automated laser welding process.

In addition, as mentioned above, heat dissipation directly affects the luminous efficiency of LEDs. At present, high-quality LED lamps have solved the problem of heat dissipation in design and technology, and can have a lifespan of more than 30,000 hours, but LED lamps with poor design or craftsmanship may only have a lifespan of several thousand hours or even shorter.

Professional development, design, strict production management, the selection of components and materials, from advanced automatic operation machinery to strict quality control of the production process (including the aging treatment of intermediate parts), each link affects LED lamps of the quality.

3 Application prospects of LED stage lighting

Although there are some problems, the prospect of LED stage lighting is unanimously optimistic.

(1) The luminous efficiency of LEDs continues to improve, and the price continues to decrease.

The power and luminous efficiency of single-die LEDs are constantly improving. The laboratory has been able to reach more than 160 lm/W (also called more than 190 lm/W), and commercial products also have efficiencies of hundreds of lumens per watt. The goal of scientists It is 200 lm/W. The power of a single die product will also be doubled.

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