How to convert the intensity of light of a star

[Padrepapp]

If you take the spectra of a star you usually have a big primary mirror (lets say 1m) to get a lot of light, and use an exposure time usually several tens of minutes.

Can one use an astronomical spectrograph for a led/arclamp light source? How does the light intensity of a star compares to conventional light sources? Will you need lower exposure times?

 

[Drakkith]

Can one use an astronomical spectrograph for a led/arclamp light source?

I don't see why not.

How does the light intensity of a star compares to conventional light sources? Will you need lower exposure times?

Probably. Most light sources are MUCH brighter than a star.

 

[SteamKing]

If you take the spectra of a star you usually have a big primary mirror (lets say 1m) to get a lot of light, and use an exposure time usually several tens of minutes.

Can one use an astronomical spectrograph for a led/arclamp light source? How does the light intensity of a star compares to conventional light sources? Will you need lower exposure times?

You use a big mirror and long exposure times to collect enough photons traveling from the distant star to make a noticeable change in the photographic plate, CCD, or whatever device or medium you are using to make a photograph or a spectrograph or whatever. One or two or a handful of photons don't make a noticeable enough difference to these media, so you must collect bunches of them from the star being observed, and that takes time.

If you use the same equipment on a nearby light source, like a candle or LED light, there are many more photons to capture; thus exposure times can be greatly reduced, lest the image become totally washed out, like an overexposed photograph.

 

[Padrepapp]

Thanks for the replies Drakkith and SteamKing,

I don't see why not.
Probably. Most light sources are MUCH brighter than a star.

If you use the same equipment on a nearby light source, like a candle or LED light, there are many more photons to capture; thus exposure times can be greatly reduced, lest the image become totally washed out, like an overexposed photograph.

So if this is true, I just wondered why don't they use echelle spectrographs in optical sciences, where you have 2 dimensional spectrum (orders on top of each others). When astronomers need high resolution they use these kind of instruments.

They use an echelle grating, and a cross disperser element like this:
http://www2.keck.hawaii.edu/inst/hires/lightpath.jpg

and the result is a spectrum with orders on top of each others:
http://www.obs-hp.fr/guide/sophie/spec_echelle_labo.jpg