
Gilway Technical Lamp
55 Commerce Way
Woburn, MA 01801
Tel: 781-935-4442
Fax: 781-938-5867
www.gilway.com
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.
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
μ
m with a cutoff wavelength
located at 5
μ
m.
A Visible/IR lamp is a very cost-effective component
for an NDIR sensor, but it has a limited IR range.
For carbon dioxide (CO
2
) and hydrocarbon (HC)
detection, it is an ideal technique.
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.
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.
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.
Spectral Transmission of the Glass Envelope for Visible/IR Lamps
and Absorption Wavelengths for Specific Gases
0%
10%
20%
30%
40%
50%
60%
70%
3.0
3.5
4.0
4.5
5.0
5.5
Wavelength (
m
m)
T
HC
CO
2
CO