What is a Spectrophotometer?
A spectrophotometer is an instrument that measures the changes in light passing through a transparent solution. What happens when light passes through a solution? All solutions and compounds absorb light to a specific wavelength. For example, haemoglobin absorbs blue and green light so appears red. But why does this happen?
Looking at the electromagnetic spectrum, visible light ranges from violet at a wavelength of 400 nm to red at a wavelength of 700 nm. Colours that we see are the colours reflected by objects and not those that are absorbed. Therefore leaves on trees appear green because they reflect green light. Haemoglobin appears red because it reflects red light.
But the spec measures the light that is absorbed, or the colours that we do not see. So to do an assay on haemoglobin, we would set our spec to around 500 -600 nm in wavelength. Most specs use light sources within the visible spectrum, but UV and IR specs are also available.