Light is crucial to accurate diagnosis

Medical examination lights are used to create the ideal visual conditions for a doctor to identify any possible medical signs or symptoms of a medical condition. These task lights produce controlled beams of high color rendering, uniformly distributed light that allows the physician to make an accurate diagnosis. The design and constructional principle of an exam light have been optimized for ergonomics, maneuverability, sterilizability, easy positioning and minimum space consumption.

A medical examination light typical has a lightweight lighthead supported by a gooseneck or articulated arm. It may be attached to a ceiling, a wall, or medical equipment such as a patient table or chair. However, mobile, flood standing lights are a more common design. The flood stands are available with fixed or adjustable height and receive stability through a weighted base. The exam light may be given mobility by four wheels which are attached to the bottom of the base. The wheel is a swivel caster that can rotate 360 degrees. The rolling stand has a braking mechanism that can lock the wheels for still positioning.

Lighting technology

As LED technology brings a whole new world of design possibilities as well as performance advantages across all aspects of lighting, LEDs have become a logical choice of light source for exam lights over halogen and xenon lamps. Gone are the days when exam lights had to be huge and power-hungry.

  • LEDs produce high intensity directional light from a small light emitting surface whereas traditional light sources produce omni-directional light distribution that requires larger reflectors to collimate the beam.
  • High source efficacy, solid state durability and long operation life are not the most prominent advantages of LED lighting when it comes to medical lighting applications.
  • Lighting attributes, such as color quality, optical distribution and intensity effectiveness can be prioritized to provide the best lighting for both the physician and patient.
  • A huge advantage of LED lighting over conventional incandescent and HID lighting is that LEDs do not emit infrared (IR) energy. Cold, IR-free radiation minimizes the risk of drying out exposed tissue and contributes to patient comfort.
  • LED technology offers the new capability of precise control of the light spectrum, which allows the spectral characteristics of the light to be flexibly adapted to the specific diagnostic procedures.

System design

Depending on the task size, the visual age of the physician, the time to perform the task and other interdependent variants, the required illuminance on the task plane varies from 500 to 2,000 lux. An LED exam light typically incorporates an integrated light engine that produces an illuminance in the range of 15,000 to 40,000 lux at 39.37” (1 m). The light engine is comprised of an array of high power LED packages that are mounted on a metal core printed circuit board (MCPCB).

A task light designed to illuminate larger objects may incorporate multiple LED modules or light engines. The LED assembly is attached to a heat sink which allows the waste heat generated at the LED junction to be transferred to the ambient air. To maximize optical delivery efficiency and ensure minimum glare the light distribution of each LED is controlled directly at the package-level using a lens, reflector, or a combination of them.

Medical examination lights are frequently required to provide illumination over a relatively small area. Individually molded compound lenses such as total internal reflection (TIR) optics have gained an enormous popularity for their ability to produce a collimated beam with little spill light. The beam spread of the task light ranges from spot to flood distributions. The emitted light should be distributed uniformly in order to support speed and accuracy of tasks. A sealed housing with smooth exterior finish facilitates surface wipe-down cleaning to prevent hospital-acquired infections.

Color reproduction

For patient examination, color has long been used as a diagnostic indicator. Quick and accurate identification of subtle differences in color to a great extent can mean the difference between life and death. Colors should be rendered accurately such that subtle changes in skin tone or tissue colors that can affect the detection of changes in health can be observed. The ability of a light source to reproduce the colors of various objects faithfully is determined by the relative amount of radiation at each wavelength across the visible spectrum.

Medical diagnosis dictates the use of LEDs with a minimum color rendering index (CRI), also denoted by Ra, of 90. The special index R9, which is not used in the calculation of the general CRI, should scale with the Ra to provide the optimum visualization of red tissues. In some markets, medical examination lights are required to report the Cyanosis Observation Index (COI). In Australia and New Zealand, for a light to be qualified for visual detection of cyanosis its COI should not exceed 3.3.

LEDs that produce white light adopts the phosphor-converted LED (PC-LED) architecture. Most phosphor-converted LEDs use a blue LED to pump phosphor downconverter within the device package. The LEDs can be designed to emit with a high efficacy. However, they produce a blue spectral peak centered somewhere in the range of about 445 to 465 nm. To achieve superior color rendering, some products use violet pump LEDs which deliver radiant power fairly broadly across the visible spectrum.

Color temperature

The spectral power distribution (SPD) also determines the correlated color temperature (CCT) of a light source. Medical examination lights typically have CCTs in the range of 4000K to 5000K. Tunable white LED products use a combination of warm white and cool white LEDs to provide a continuously adjustable range of color temperatures.

Drive current regulation

LED exam lights can be line-powered or battery-operated. An integral LED driver regulates the power to the LED array while suppressing ripples to enable flicker-free lighting. The driver circuitry may incorporate multi-level or continuous dimming capability which allows lighting to be adapted to various applications. On/off switching and dimming can be made a membrane keypad. Some products are equipped with a wave-activated IR sensor switch for touch-free operation.