EL Panel spectral content

Forums Spectroscopy Flats EL Panel spectral content

Robin Leadbeater

Hi Kate,

I found my Gert Neumann panel and put it in front of the ALPY 600 spectrograph with an ATIK 428 camera. Here is the comparison between the EL panel and the internal ALPY lamp.

 (This is effectively the output from the light source x the response of the grating and CCD camera)

As claimed by the supplier, the spectrum of the EL panel  is smooth with no obvious lines (The small scale ripples in both spectra are from the camera QE and demonstrates one of  the reasons why flat correction is important).

The EL panel could potentially be used as a flat light source for spectroscopy, even though the spectrum shape is very different from the Incandescent Halogen lamp black body curve but unfortunately there is no light from it below 4000A. (The internal Halogen lamp in the ALPY also struggles in this region but in practise it still gives enough output down to ~3600A provided a large number of flat exposures are combined to reduce the noise)

A key difference between imaging and spectroscopic flats is that it is much less important that the field is evenly illuminated since you are only sampling a small slice of the field. Even some variation in illumination along the slit is not important if you are measuring at one position eg as for a star. This means even a crude flat illumination setup can be used. I bought my ALPY before the calibration module came out and used the same flat lamp setup as I used for my LHIRES – A halogen lamp waved a couple of metres in front of the telescope aperture which was covered by a diffuser (actually a pillow case!), similar to Christian Buil’s setup here


This worked well and I saw no difference when I eventually got the calibration module



EDITED: to mention the grating response