The LED should turn green after the spectrometer has time to warm up. If it does not turn green, first turn off the instrument, then unplug the USB cable and the AC power. Plug back in the AC power, turn on the instrument, and wait for it to warm up. Plug in the USB cable and open Logger Pro or LabQuest App. If it continues to stay red, you should try to check the performance by seeing if it will collect data.
The red LED is not necessarily an indicator that the bulb needs to be replaced. If the light source (deuterium or tungsten) goes out, it will be noticeable in the absorbance spectrum and in uncalibrated mode. The spectrometer may also not be able to complete a calibration if the light source is out.
If you are unable to take data or if the data is irregular, contact chemistry technical support at firstname.lastname@example.org