The Status Quo and Application Analysis of LED Stage Lighting

1 LED stage lighting status

1.1 Overview of technology development

Since the emergence of blue, white and high-brightness LEDs in the 1990s, the luminous efficiency of LEDs has been continuously improved. Commercial LED tubes have reached luminous efficiencies of 50 lm/W to 100 lm/W, and their luminous efficacy is still Increasingly, it is estimated that it will eventually reach 200 lm/W, not only much higher than 10 lm/W~30 lm/W incandescent lamps (including tungsten halogen lamps), but also much higher than all current 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. The stage lamps are powered by kilowatts of power and tens of thousands of lumens. Therefore, many people have never thought of using LEDs before. On stage lighting.

At the beginning of this century, blue LEDs became popular, white LED technology gradually matured, LED light efficiency was doubled compared with incandescent lamps, and high-power (watt-level) LEDs can last for tens of thousands of hours. At the same time, it also has switches that are fast and tuned. With the convenience of light, new LED stage lighting fixtures that combine multiple LEDs to increase total luminous flux are beginning to emerge. At first, due to technical reasons and expensive prices, such lamps are less popular. In recent years, due to the improvement of the luminous efficacy of LED lamps, the popularity of components such as concentrating cups, dies, and casings, many manufacturers have begun assembly and production. LED lamps attract people to try with their bright colors, energy saving and environmental protection.

Some fixtures used LED luminaires and achieved good results.

At present, there are two modes of LED for white light illumination: one is to add a phosphor to the blue-emitting die, so that part of the blue light emitted is converted into yellow light by the phosphor, and some blue light and yellow light are mixed into white light; The other is to use three LED tubes that respectively emit red, green, and blue light, and mix to form white light. The former method used for TV lighting is mostly used, and the latter method for stage lighting is mainly used.

1.2 LED advantages for stage lighting

LED luminaires can be used for stage lighting thanks to several key features:

(1) Energy saving and efficient.

Compared with incandescent light sources (including tungsten halogen light source), LED lamps are characterized by energy saving and high efficiency. We can observe this by comparing the two lamp structures.

a. The efficacy of incandescent lamps. Among the commonly used incandescent concentrating lamps, the incandescent bulb as a light source is bulky, and a reflector and a concentrating lens structure are often used. One of them is a spherical mirror, the filament is located in the spherical mirror sphere, and the spherical surface reflects the light that is directed toward the rear of the lamp back to the filament. Since the filament is located near the focus of the front condenser lens, the light emitted by the filament will be collected by the condenser lens. Convergence into a beam of nearly parallel beams, as shown in Figure 1. The light path can only use a part of the light emitted by the light bulb, plus the loss of the mirror and the lens, the luminous efficacy of the entire lamp is only about ten percent.

b. The efficacy of halogen tungsten lamps. The currently more efficient ellipsoidal mirror imaging spotlights benefit from the miniaturization of halogen bulbs, as shown in Figure 2, where the filament is located at a focal point inside the ellipsoidal mirror.

Due to the characteristics of the ellipsoid, it has two focal points, and the light emitted from one focus will be concentrated in the other focus after being reflected by the ellipsoid. The focus of the concentrating lens in front of the luminaire is close to the second focus of the ellipsoidal mirror, and the light emitted by the light source through the second focus can be concentrated into a bundle of parallel rays. Since the bulb is filled with halogen, the process and material of the filament and the bulb are improved, the bulb size is reduced, and the bulb is deeply wrapped in the ellipsoidal mirror. The ellipsoidal mirror has a large tolerance angle to the bulb, and therefore, the bulb emits Most of the light is used, the light efficiency of the lamp is higher than the previous one, up to 40%~50%.

c. The efficacy of LED lamps. At present, the common LED beam lamp uses a dedicated collecting cup, and the LED light emitting diode is installed in a fully transparent collecting cup. The middle of the concentrating cup is a convex lens, and the light beam emitted from the LED tube at the focus of the convex lens is gathered into a parallel beam, and the beam emitted from the side of the LED tube enters the inner side of the concentrating cup and then refracts to the outer side of the concentrating cup, due to The outer side and the inner side of the collecting 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 collecting cup, so that refraction is impossible. The total reflection is generated from the front, and after reasonable design, the outgoing light will become parallel rays parallel to the optical axis of the lamp, as shown in Figure 3.

The high-power LED tube has a highly efficient mirror inside, which is a unidirectional light source.

A small collecting cup can use almost all the light emitted by the LED tube and 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 concentrating cup is close to the LED, it can still be made of high-transparency polyester plastic, and it will not be deformed by high temperature. Well-designed, molded-shaped concentrating cups are produced in batches with good consistency.

The LED tube and the concentrating cup are combined into one module, but the luminous flux is not enough. Generally, one and the same module is combined again to form a planar LED array, as shown in Fig. 4, thus, one hundred The light emitted by the multi-watt LED luminaire is equivalent to the brightness of a few hundred watts of tungsten incandescent lamps, which can meet the needs of stage applications and meet the requirements of energy saving.

Some people refer to the optical design inside the LED as a design, the concentrating cup is designed as a secondary design, and the combination of the concentrating cup module is the third design. The flat type of collecting cup module assembly process is relatively simple. Since the parallel beams emitted by each module overlap in the same plane, the entire luminaire emits a beam of slightly divergent parallel light, which is illuminated by a large number of LEDs to produce glare 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, LEDs use its small size and low temperature to adopt a more efficient optical path design. The utilization of the luminous flux of the light source is several times higher than that of the incandescent stage lighting. The two factors are superimposed, and the same luminous flux, incandescent lamps are several times larger than the power of LED lamps. Therefore, smaller power LED luminaires can meet the light intensity requirements required by the stage.

(2) The color is bright and bright.

In the stage performances, the lights are used to color the stage sets, props, costumes, or to create a specific stage atmosphere, and the stage performances use a lot of colored light. Compared with the color light commonly used in stage lamps, LED lamps have better performance in color than traditional light sources. In the past, the color light used in stage lighting was a method of adding colored color filter paper or other color filters in front of white-emitting lamps, that is, blocking unwanted color light and passing only the desired color spectrum. Since a large amount of unwanted color light is blocked, the emitted color light is rather weak, especially the commonly used blue light, whose spectrum is at the high end of the visible spectrum. Due to the characteristics of the human eye, the red and blue-violet colors at the ends of the visible spectrum are not particularly Sensitive, a large number of sensitive light is blocked, and the luminous efficiency of the luminaire is even lower.

At the same time, in order to prevent the color filter from fading at a high temperature, the color filter transmits a large amount of infrared components in the spectrum, and the blue color filter transmits short-wavelength blue light, and some long-wavelength red light transmits. Therefore, the blue light obtained by the method of adding a blue color filter before the incandescent lamp is not only reduced in brightness but also in color, which is difficult to satisfy the lighting engineer.

LED luminaires, on the other hand, emit red, green and blue light from three light-emitting tubes. White light is mixed by three primary colors. When a certain color of light is needed, only the unwanted spectrum is emitted, and the desired spectrum of light is emitted. In this way, the luminous efficiency of the lamps is greatly improved. Especially for blue light, the blue light brightness of the LED lamp is equivalent to the brightness of the incandescent lamp plus blue color paper which is ten times higher than the power. The color light of LED lamps sometimes appears too pure and bright in actual use. In order to reduce the saturation of color light, some LED lamps also add white LED beads to produce a light color.

Since the luminous efficiency of LEDs is higher than that of incandescent lamps, the luminous efficacy 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 performance to produce the required color light, which can fully utilize the advantages of LED. .

(3) The life expectancy is extremely long.

LEDs have a lifespan of tens of thousands of hours, while incandescent lamps have a lifespan of only a few hundred and thousands of hours. However, when the LED lamps were developed in the early stage, the LEDs were installed in the lamps and the heat dissipation problem was difficult to solve, which greatly shortened the life of the LEDs and affected the promotion of the LED lamps. The LED tube is semiconductor light-emitting. At the current state of the art, 10%~20% of the input energy of the LED is converted into visible light, and the remaining 80%~90% of the electric energy is converted into heat. These heat energy must be dissipated in time. Otherwise, Will cause the die temperature to rise. If working at room temperature, LED life can reach five to 100,000 hours.

As a stage light fixture, many LED tubes are brought together, and the temperature of the LED tube will rise, which will result in a decrease in the luminous efficiency of the LED tube and a shortened life.

At present, the general power type LED tube structure has been greatly improved, not only has a heat-conducting substrate itself, but also is equipped with an aluminum-based metal core printed wiring board (MCPCB) as a heat-dissipating substrate, which facilitates the heat generation of the internal chip. In addition to a heat sink with sufficient heat dissipation area or with heat dissipating fins, the entire thermal conduction path from the LED tube body to the outside of the lamp body is also very scientific, if the operating temperature of the internal LED chip is controlled within 100 ° C (the limit temperature of the LED is At around 150 °C, the life of the LED can reach tens of thousands of hours.