In the spectral images here the wavelength of light decreases from left to right. Long wavelength red is shown on the left progressing to short wavelength blue on the right.

Atomic spectral lines are generated from specific electron transitions which take place inside the gas atoms within the lamp arc. The emission (light) is generated every time an atom transitions between an ionised to stable state. These are unique 'finger prints' of the gasses which can be used to identify the light source.  

'Clicking' on the spectrum image takes you to the lamp that emits it.

Discharge Lamp Spectrum

The images shown below were taken with a diffraction grating and a digital camera.  Positioning, focusing and preventing light saturation in the camera were difficult to control. As a result the images have limitations.

Neon sign                                                                           NEON                                             Image 1

Image 1 is of Neon. This is one of the more difficult spectrums to capture as the light intensity is a fraction of the output generated by the rest of the HID (High Intensity Discharge) lamps. The source used was the neon sign question-mark on the main page.                   

MBU/F Lamp                               MERCURY Blended FLUORESCENT Image 2

Image 2 is the output from a 250W MBF/U lamp. The red lines are due to the fluorescent coating on the outer bulb converting UV to a visible red.  This red emission attempts to improve the light output to a more white appearance. 

MB/U Lamp                                        MERCURY VAPOUR                 Image 3

Image 3 is a  250W MB/U lamp. This is a high pressure mercury lamp without the fluorescent coating. The line emissions are purely from the mercury vapour and the light has a greenish-blue appearance.

MBI/U Lamp                                     MERCURY HALIDE (Green) Image 4

The lamp shown here has some other elements added to the arc. By adding halides different colours are made possible. 

MIT 70W Blue Lamp                           MERCURY HALIDE (BLUE) Image 4a

Similar to the above this lamp emits mostly blue light.             

HPI-T Plus Lamp                                MERCURY HALIDE (White)  Image 5

Figure 5 is from a white mercury halide source. This produces a cool white light with good colour rendering qualities. It can be seen from the spectrum that there is a good balance of Red/Orange, Green and Blue outputs. This is fundamental for a white light to be produced.

SOX Lamp                                          SODIUM VAPOUR        Image 6

Figure 6 is of sodium vapour. Almost all of the light output from a sodium lamp is contained in just two yellow lines. These are so close together that my diffraction grating set-up could not resolve them and just one fat line is shown here.

SON/T lamp                                      HIGH PRESSURE SODIUM Image 7

Figure 7 is of the light output from a high pressure sodium lamp. Right away, you know there is more than just sodium in the arc tube due to the extra visible lines. Mercury is the additional element.  Vapours operating at high pressures only create line broadening due to Doppler-shift as the atoms speed up in the higher temperatures. Blending the sodium and mercury improves the light output colour and still keeps the lamp reasonably efficient.

Cd Spectral Source Lamp                      CADMIUM VAPOUR               Image 8

Figure 8 is of a Cadmium spectral source. This lamp is designed for laboratory use and the electrodes are shielded to prevent light emission from the glowing electrodes being observed.

H1 Xenon car head Lamp                      XENON HID                  Image 9

Figure 9 is from a Xenon car driving lamp. Like the mercury halide, these lamps are not just xenon gas. There are additives to improve the light colour and intensity.  This lamp has a colour temperature of  4300K.

Hydrogen Spectral Source                     Hydrogen                                   Image 10

The simplest atom's spectrum