Several modern printers will accept one of the gate photometers on the market mounted at the exposure gate.
This allows the light to be read in terms of intensity and colour and adjusted by changing filters or trim settings back to a pre-set level. These photometers are of great value when a lamp blows, and are very precise at measuring and restoring intensity levels when dealing with a replacement lamp of the same model.
None are very precise in recording colour balance and this is probably because the response of the photocells used in gate photometers is not similar in response to a colour print material's sensitivity. Nevertheless these are valuable if expensive instruments and shorten the trial and error testing of new lamps and equipment.