What should an Intensity Spectrum look like for a brand new FLD?

There are no limits for the Intensity Test on an FLD, but two things need to be checked: Firstly, the absolute maximum (close to 15000 at ~310nm in the manual, about 4800 at ~490nm with your FLD). Again, there are no limits and we don't specify where the maximum should be, so your results might still be okay, if you e.g. excite at 420nm and get the emission at 490nm. Secondly, there should be a steep increase in the baseline in the low UV area, where yours is a bit shallow. If the intensity is too low (anything below 3000 or 4000 counts I consider to be poor), it might be difficult to carry out the Wavelength Calibration with Glycogen.

Different to UV detectors the lamp is not to be replaced as a first step. An Agilent engineer might need to check the parts in the optical unit, such as EX condenser, lamp house window, mirror and EX monochromator. Cleaning hardly ever helps, as those parts suffer from degradation over time (being constantly bombarded by powerful UV light). Certain parts, like mirror and monochromator must not be cleaned at all; they will get damaged if this is tried.

I believe what you see is really degradation of the optics.

Make sure to treat your flow cell right. Always use fresh, best quality water and never leave the cell in water or buffer. If not in use, store it in IPA.

Thank you so much! You have been very helpful :)