Visible/IR Lamps for
NDIR Gas Sensors
Gilway offers a line of Visible/IR lamps for use in
applications such as nondispersive infrared gas
sensors, analyzers, and monitors.
Nondispersive Infrared (NDIR) sensors are simple
spectroscopic devices often used for gas analysis.
The key components are an infrared source (lamp),
a sample chamber or light tube, a wavelength filter,
and an infrared detector. The gas is pumped or
diffuses into the sample chamber, and gas
concentration is measured electro-optically by its
absorption of a specific wavelength in the infrared
The intensity of IR light that reaches the detector is
inversely related to the concentration of target gas
in the sample chamber. When the concentration in
the chamber is zero, the detector will receive the full
light intensity. As the concentration increases, the
intensity of IR light striking the detector decreases.
Beer’s Law describes the exact relationship
between IR light intensity and gas concentration:
Beer’s Law:
I = I0e
I = the intensity of light striking the detector
I0 = the measured intensity of an empty sample
k = a system dependent constant
P = the concentration of the gas to be measured
The IR light is directed through the sample chamber
towards the detector. The detector has an optical
filter in front of it that eliminates all light except the
wavelength that the selected gas molecules can
absorb. Other gas molecules do not absorb light at
this wavelength, and do not affect the amount of
light reaching the detector. The IR signal from the
source is usually chopped or modulated so that
thermal background signals can be offset from the
desired signal.
For greater optical efficiency, a reflector assembly
can surround the lamp used for the NDIR sensor.
The reflector is usually parabolic in shape to
collimate the IR light through the sample chamber
towards the detector. The use of a reflector can
increase available light intensity by two to five
times. The reflector surface can also be goldcoated to further enhance its efficiency in the
NDIR sensors can be used to measure practically
all inorganic and organic gases, but are most often
used for measuring carbon dioxide because no
other sensing method works as simply and reliably
for this gas. Calibration gases of specific
concentration are available for determining the
system constant k for any particular sensor design.
Applications for NDIR Gas Sensors
indoor air quality
cycle regulation in self-cleaning ovens
automotive and flue gas emissions
greenhouse farming
hazardous area warning signals
gas leak detection
landfill gas monitoring
alcohol breathalyzers
patient monitoring for anesthesiology
Gilway Technical Lamp
55 Commerce Way
Woburn, MA 01801
Tel: 781-935-4442
Fax: 781-938-5867
The most desirable lamp characteristics are:
§ high IR output
§ accurate filament position
§ small size
§ long lifetime
§ low thermal time constant
The last characteristic is important if the lamp
power supply is to be modulated during operation to
offset thermal background signals.
The NDIR gas sensor needs an infrared source for
the excitation of the gas molecules. Thermal
radiators such as Gilway’s Visible/IR lamps are
often employed for this task. Their operating
temperature should be as high as possible to obtain
a large output intensity and detector signal. Glass
envelope lamps operate at higher filament
temperatures when compared to other filament or
ceramic heating elements. The envelope can be a
gas-filled or a vacuum. However, the transmission
of the glass envelope limits the useful spectral
range, and constrains the types of gas molecules
that can be measured by NDIR.
Gilway Visible/IR lamps feature thin glass
envelopes that reduce infrared absorption and
provide more output in the infrared. Double-coiled
filaments operate at high temperatures, and are
rugged and geometrically precise for applications
requiring broad spectral emission and superior
optical performance.
The transmission characteristics of a typical lamp
glass are illustrated below together with the center
wavelength of some common gas absorption
bands. The intensity of the IR light decreases
significantly above 4 µm with a cutoff wavelength
located at 5 µm.
Gilway Visible/IR lamps are offered in T-1 and T-3/4
sizes with wire leads or bi-pin bases and operate at
5 volts. Several versions are available that operate
from 45 mA to 150 mA with rated lifetimes from
5,000 to 100,000 hours. Gilway also offers a large
line of reflector lamp assemblies with both fixed and
adjustable focus options. Please contact the sales
department at Gilway Technical Lamp to request a
product catalog.
A Visible/IR lamp is a very cost-effective component
for an NDIR sensor, but it has a limited IR range.
For carbon dioxide (CO2) and hydrocarbon (HC)
detection, it is an ideal technique.
Spectral Transmission of the Glass Envelope for Visible/IR Lamps
and Absorption Wavelengths for Specific Gases
Wavelength (µ
Gilway Technical Lamp
55 Commerce Way
Woburn, MA 01801
Tel: 781-935-4442
Fax: 781-938-5867