Hi Irena Fryc, thank a lot for your kind answer.

So I have tried with different "Scan time", from 1 second to 20 second in each point, but the image is very similar to that images I showed before.

The noise of the signals between 700-570 nm diminute considerably when the scan time is increased from 1 to 20 seconds. The profile of the spectra below 570 nm is quite similar. I made the scan between 400 to 700 nm.

 What happens with no cells and with cells containing pure water?  

- Scan time will not really influence this problem.

- it is not "saturation". At zero absorbance, the full light intensity reaches the detector, and it copes well with that. After all, the baseline portion of the spectrum from 600nm to larger wavelengths is the only part that seems to be OK.

- In contrary, a very weak light source should give spectra with large noise.

=> Please: show us a scan from measuring only air, and another from measuring something black (blocking light completely)

Hi dear Friends

I really appreciate all your suggestions.

follows the spectra of the Rhodamine B (10mg.L-1), blue line;

            the spectra of the blanck sample (distilled water)  orange line;

          the spectra of the air ; red line

I took the massage from the equipament that says " wavelength calibration error".

what should i do to recalibrate?

Thank you

In case the software gives an error message saying " wavelength calibration error", then of course you should follow the respective guidance from the instrument manual. Either there is something described you can do yourself, or it tells you to call the service hotline/ manufacturer.... Ether way you should do it so.