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Just what exactly should users be looking for when it comes to choosing medical lighting? The criteria will be different if specifying a major Operating Theatre Lamp from a Minor Surgical Lamp - but there are some similarities.

Many specifiers of surgical lamps choose products just on their light intensity. Although this is an important parameter, it is only one of several important criteria. A little bit like choosing a car without knowing the maximum speed and acceleration!

An operating lamp must provide the following key features:  
 

Area of Illumination Colour of Light
An adequate area of illumination -large or medium sized depending on types of surgery).   
The colour of light is extremely important. Correct colour makes it much easier to visualise human tissue and minimise eye fatigue amongst surgeons.
  
Cold Light Shadowless Light
Cold light is important for both patient and surgeon. The "heating" effect of radiation from the operating lamp dries patient tissue and can cause discomfort to surgeons, especially during prolonged procedures.
  
An object placed between the surgical light and the patient should not throw distracting shadows or severely reduce the available light intensity.

All operating theatre lamps use projection techniques to throw light around obstructions. A good system will minimise cast shadows, but a reduction in light intensity is inevitable as light only travels in straight lines (in earth bound physics).
  
Uniformity Deep Cavity Penetration
 
Uniformity of the illuminated light field is rarely used as a parameter in specifying lamps, but it is crucial to performance. A high light intensity is easy to achieve if all the visible light energy is concentrated into a small area! Good surgical lamps must produce an intense illuminated area with high uniformity from the centre to the edge. This is a major contributor to reducing eye strain
  .		 Whilst shadow reduction requires light to be projected from as wide a range of angles as possible, good deep cavity illumination is achieved by projecting light from the centre of the lamp directly into the cavity. A good opererating lamp must achieve both these requirements.
Depth of Focus Focus Control


Depth of focus refers to the focused column of light a lamp produces, similar to depth of field in photography. Lamps with low "depth" have to be moved more frequently during surgery to keep the surgical zone within the field of focused light.

 
  
Focus control allows the user to move the column of focused light closer or further away from the lamp without having to move the lamp head. This can usually be done by the surgeon using a sterile handle. The same facility can be used to spread the light beam to cover a larger area, or to adjust the light intensity to concentrate or diffuse the light beams.
  
Manoeuvrability Aerodynamic Performance
As many operating theatres are multi-functional, all relevant procedures should be taken into account. Lamps for orthopaedic procedures are moved extensively in contrast with others where a stationary lamp is required. Six rotating joints provide optimum manoeuvrability.
  
Laminar flow canopies are being increasingly used in operating theatres to reduce the incidence of infection. Most operating lamps (made from solid mono-bloc constructions) severley disrupt laminar airflow by either blocking its path or deflecting the air like an aerofoil.

There are no commonly accepted measurements of aerodynamic performance but empirical tests show that reticulated (space frame style) designs provide excellent performance.
  

 
Although these 10 factors should always be considered, there are at least as many smaller considerations. If you would like to know more details, I shall be pleased to answer questions
e-mailed to me.
 
Nigel Davil is the leading British expert on operating theatre lamps. He is the advisor to the British Standards Institute on Surgical Lamps and represents BSI on the International Standards Committee. He is currently engaged with IEC draft 60621-2-41d.

As Technical Director of Brandon Medical, Nigel is responsible for the successful development of Galaxy Ultra and for ensuring compliance with forthcoming regulatory standards.

Above Right: Technical Director - Nigel Davil

 


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