Working principle and technical characteristics of moving head lights

       

Moving head lights are commonly used on stages and in public squares, playing a significant role in advancing lighting technology. Professional moving head lights integrate electronics, mechanics, and optics, making them high-tech products. Qualified professional moving head lights must be stable and reliable, provide excellent light efficiency, accurate positioning, good heat dissipation, and the structure and materials must meet ergonomic requirements.

Classification of Professional Moving Head Lights

       Professional moving head lights are categorized by power usage into types such as 250W, 575W, 1200W, and 350W, with 1200W being the primary type used in professional performance venues. This article focuses on analyzing the structural principles of the 350W moving head light. In summary, a moving head light comprises three main systems: optical, mechanical, and electrical with program control. These systems are interconnected and work together to meet requirements for light, color, speed, direction, effects, heat dissipation, noise, and positioning.

Optical System

       The primary goal of designing the optical system is to maximize the utilization of the luminous flux from the light source. Key indicators include light intensity, uniformity, saturation, and spot size. Two main factors affect these indicators: the light source and the structure and material selection of the optical system. Currently, OSRAM or PHILIPS 350W short-arc double-ended metal halide lamps are recommended by manufacturers and users worldwide. These lamps are compact, bright, have high color temperature and good color rendering, and can maintain relatively stable color temperature during dimming. However, they may have issues with the layering of fillers, creating color bands in the arc image or shadows in the arc tube, which need to be minimized through optical design. Parabolic mirrors can be used for uniform mixed light beams, while mirrors with scales or surface textures are suitable for divergent or narrow beams. Reflector systems made from mirror materials are preferred over refractor systems. When multiple beams are needed from a single light source, prism or lens combinations can be used. Currently, 350W moving head lights use lens combinations in their optical designs, consisting of aspherical (parabolic) quartz lenses.

Mechanical System

        The mechanical system encompasses a wide range of aspects, including materials, structure, mechanical performance, housing requirements, and heat dissipation. The main considerations for selecting lamp materials are functionality, manufacturability, and cost-effectiveness. Internationally and domestically, 350W moving head lights primarily use steel, plastic, and aluminum alloy. The structure model is designed with different materials used for different parts, such as plastic for the lamp housing, and aluminum alloy castings, stampings, or turned parts for the support frame, base, side panels, and end plates.

        The structure of the lamp determines its mechanical performance, heat dissipation, strength, noise, and weight. Both international and domestic 350W moving head lights use dual-arm support structures, with the lamp body rotating horizontally up to 540° and vertically up to 255°. The base must be reinforced to support the requirements for hanging and inverted installation. The mechanical performance of the lamp body mainly depends on the mechanical strength of its components, ensuring no deformation, wear, corrosion, vibration, or compression issues during continuous operation. The housing must meet strict waterproof, dustproof, anti-static, and moisture-proof requirements, with different protection levels for indoor (typically IP20) and outdoor (typically IP44) use.

Electrical and Program Control

1. Electrical Characteristics and Circuit Design

       Currently, most professional 350W moving head lights use rare gas discharge lamps. Their startup and stable operation depend on circuit design, power supply, and components like ballasts. Rare gas discharge lamps do not require stabilization time after startup. To ensure stability, the difference between the circuit's maintenance voltage and the lamp's instantaneous voltage must be sufficiently large throughout the AC cycle.

        The startup, stability, shutdown, and restart of the light source should be designed according to its characteristics. The startup voltage of rare gas discharge lamps is very high, requiring transformers, starters, or half-resonant circuits to increase the instantaneous startup voltage. The stability of the light source after startup depends on the matching of ballast and circuit parameters. Ballasts prevent current runaway and ensure the light source operates within its normal electrical characteristics. Two types of ballasts are commonly used: inductive and electronic. Inductive ballasts are stable but heavy, requiring higher strength for the lamp body and handling. Electronic ballasts are lighter and easier to handle, but have higher design and maintenance costs.

       For re-ignition, conventional circuit designs make it difficult to immediately restart the light source due to high temperatures forming vapor pressure resistance within the lamp. The gas pressure must be reduced to cold state values before re-ignition can occur. Currently, both international and domestic manufacturers use conventional circuit designs for this purpose.

2. Program Control

         Currently, both international and domestic moving head lights commonly use DMX data format for programming. DMX512 data flow speed is 250K, with each BIT being 4 microseconds. DMX data format includes: IDLE or no DMX situation, BREAK (88 microseconds low level signal), MARK AFTER BREAK (8 microseconds high level or 2 pulses), START CODE (11 pulses or 44 microseconds), MARK TIME BETWEEN FRAMES (0-1 second high level), CHANNEL DATA (1-512 or less), and MARK TIME BETWEEN PACKETS (high level after data transmission).

       The effects of moving head lights are achieved through different gobo patterns, color changes, viewing angles, horizontal and vertical beam angles, speed variations, strobe effects, aperture size changes, and focus adjustments. These attributes are controlled by stepper motors, with their electrical operating parameters defined and programmed to control the moving head light.

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