Visual Spectrophotometry

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Because our students are most familiar with the visible region of light, it is to our advantage to use this region when building on their understanding of light spectroscopy (or spectrophotometry).   MicroLab’s handheld visual spectrometer integrates components of a bench top spectrophotometer but in a portable format allows your student to actually look at the spectra in full color.

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Spec03The sample compartment is raised slightly above the level of the reference beam, allowing your students to simultaneously view both reference and the sample spectrum as seen here.

Generally speaking, we can say that the color of the wavelengths absorbed are the compliment of the color exhibited by the object, e.g., potassium permanganate is purple because it absorbs wavelengths in the green range, as shown in the spectrum below, purple being the compliment of green. See graph and spectra below.

Spec04Any object that is a source of visible light, i.e. it emits visible light, e.g., light bulbs, light emitting diodes,  (LEDs), gas discharge tubes, the sun, etc. can be examined for the visible wavelengths of light they emit. The diffractive grating housed within the visual spectrophotometer disperses and separates the light for students to view atomic line spectra, shown at left for a helium gas discharge tube, or the continuous black body spectrum of an incandescent light (bottom spectrum below).  Again, both spectra can be viewed simultaneously using a fiber optic cable to direct the light from one source and aligning the other source through the slit opening.  Application of the powerful NIH image analysis software allows students to convert photos to graphs.  For more information, check out our series of videos or brochure on visual spectrophotometry.

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