What is the difference between spectrometer and photometer?

 spectrophotometer have a wide spectrum of filters for measuring the absorbance of all light waves eg350 nm to75o nm or more so that it can measure the absorbance of coloured light waves + coulourless light infra red and ultra vilot + also it can read the absorbance of normal light waves which waves lies between infrared waves and ultravilot waves.
 photometer  read only by light filters which can measure only the normal light waves between the ultravilot and the infrared light waves and cannot read the apsorbance of ultravilot and infrared waves.
 

The photometer just measures the intensity of light.  Think of a solar cell hooked up to a voltmeter.  The higher the intensity of the light, the higher the reading on the voltmeter ( a simplification, but you get the idea).A spectrophotometer has a more sophisticated system of separating the light into the individual wavelengths and measuring the intensity at each individual wavelength.  Typically, a spectrophotometer has a monochromator (for separating the individual wavelengths of light) and is a scanning instrument.  As an example, it will scan from something like400 nm to200 nm at100 nm per minute.A spectrometer is a scaled down spectrophotometer.  It can use diffraction gratings to separate the individual wavelengths.  Commonly, this type of instrument is used in fourier transform  (FT) instruments.  These instruments can be for many ranges of light, including IR, UV, VIS, etc.Theoretically, a spectrophotometer is the best.  Don't always count on this.  Many of the spectrometers offer faster speed and similar resolution to spectrophotometers.  They are often cheaper, using computer power instead of optics to separate the wavelengths of light.