Maintaining a surgical lamp
o Principles of operation
function
use
scientific principles
o construction
components
system diagram
inputs/outputs
o troubleshooting
identifying common faults
replacing components
rectifying faults
o safety considerations 13.6.3 Maintaining a surgical lamp
user and patient safety
Unit B 13.6 Maintaining theatre and surgery equipment
electrical safety
Module 279 18 B Medical Instrumentation I
dr. Chris R. Mol, BME, NORTEC, 2015
Surgical lamp: Lighting function
Operating rooms can have several lighting sources.
• General room lighting in the ceiling. Used during the set up of the rooms,
cleaning and as lighting for the staff who are not working in the sterile field.
• The overhead operating room lights. These can be large reflectors with
one or more bulbs in them, mounted on a counter-balanced arm that
can be positioned over the site of the operation. These units have a
sterile positioning handle that is often adjusted over the period of the
• operation.
Sometimes: a mobile operating room light. These are large reflector lights that roll
from room to room. They simply plug in to a 220 volt outlet and are positioned as
needed by the surgeons.
• Sometimes: a personal head light that a surgeon wears. This
is a lens that focuses light transmitted to it by a fiber optic
cable from a remote light source. This light source may have
a multitude of bulbs in it that can be switched into use via a
knob on the top of the unit.
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
Surgical lamp: Scientific principles
Illumination level is measured in foot-candles or lux (1 foot-candle equals 10.764 lux).
• At 1 or 2 foot-candles, a room is considered darkened, but large objects can be
seen.
• 20 to 200 foot-candles are required for reading and other common visual activities.
• The Illuminating Engineering Society of North America (IESNA) recommends a
minimum illumination level of 2,500 foot-candles at the surgical site when the light
is positioned one meter above the site.
• Some surgeons prefer 3,500 foot-candles or more for certain procedures.
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
Surgical lamp: Scientific principles
Colour quality is a measure of the spectral content of the light, expressed by colour temperature in
kelvin (K)
• The noon sun yields a colour temperature of 5,000 to 6,000 K
• low colour temperatures cause objects to take on a reddish tint, and high colour
temperatures cause a bluish tint.
• Under most common lighting conditions, exact colour temperature control is not crucial
because of the adaptability of human visual perception; however, because lights in the OR
are often illuminating dark red tissues, they must deliver visible red light to accentuate
contrast and tissue differentiation.
• A colour temperature of 4,000 K will provide adequate brightness and allow the surgeon to
distinguish true tissue colours with minimal eyestrain. While IESNA states that an acceptable
range for surgical lights is in the 3,500 to 6,700 K range, most surgical lights operate in the
4,000 to 4,500 K range.
• Distracting differences in appearance can occur if adjacent objects are illuminated by light
sources with significantly different color temperatures.
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
Surgical lamp: Construction
Most operating lamps work directly from the
outlet power through a switch.
Some lights have dimming circuits. Older
dimmers often work with a rectifier or a
variable transformer (variac) gradually varying
the voltage applied to the lamp and therefore
the intensity of the light delivered.
The overhead operating lights have control boxes on the wall where the
intensity control is located along with the on/of controls.
This control box usually contains an SCR (silicon controlled rectifier) control
board, or transformer that powers the lights at some voltage under 115 volts.
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
Surgical lamp: Construction
Some operating room lights use fluorescent bulbs (low-pressure mercury-vapor gas-discharge lamp that
uses fluorescence to produce visible light).
Fluorescent bulbs generally operate through a transformer
and use a starting circuit. In some cases, the bulb is
heated before the starter is engaged. The heat causes
both a change in the internal tube pressure and an
increased electronic flow between the electrodes. A high
voltage (25,000 V) spike from the starter establishes an
arc in the atmosphere between the electrodes. After the
initial spike, the bulb will operate at a low current and
temperature.
The operation light must be connected to
an emergency power system …
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
Surgical lamp: Trouble shooting
Many of the surgical lamp problems associated are mechanical: they do not
stay in the position selected and the counter weights have to be adjusted.
A secondary problem is that one or more of the lights will burn out giving dark
spots in the surgical field.
Preventive Maintenance:
• cleaning
• lubricating
• visual inspection for damage or abnormalities
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
Surgical lamp: Trouble shooting
Conventionally, surgical lamps can be xenon, quartz-halogen, mercury-vapor or metal halide. These
bulb types are not interchangeable because of the voltage supplying the bulb, the connector for the bulb
and the heat generated by the bulb. The bulbs have a life expectancy of about 250 hours and need to be
monitored for replacement.
When replacing bulbs care must be taken to avoid touching the reflector part of the bulb as that can
affect the brightness at the surgical site. Also, avoid touching the bulb itself. Your fingerprints can cause
excessive heating of the glass, dramatically shortening the life of the bulb. If the glass of the bulb has
been touched, clean the fingerprints off with alcohol.
It can be very difficult to find and/or import replacement light bulbs. While it may be possible to wire a
replacement socket for a more readily available bulb, the engineer must be sure to consider size, voltage,
temperature and materials. It maybe more prudent to start with a readily available bulb and socket and
design a completely new fixture.
Although more expensive than conventional surgical lights, LED lights have several practical advantages.
They generate less heat and have much longer life cycles than traditional lights.
LED surgical lights now represent the majority of new installations.
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
Surgical lamp: Safety considerations
The highest intensity lights can cause blindness if you look directly into the light. The light should not
be used if the cover glass or filter system is damage or destroyed.
In placing the light to begin work, your eyes should be more than sixty centimeters away from the source.
Make sure that the cable carrying the main supply is well insulated and of good quality to prevent
electrocution, thereby applying safety.
Make sure that the wheels of a mobile lamp are always in good condition for stable standing.
Because if the wheels are not in good condition the equipment can fall causing instant injuries.
dr. Chris R. Mol, BME, NORTEC, 2015 Maintaining a surgical lamp
END
The creation of this presentation was supported by a grant from THET:
see https://www.thet.org/
