Goldilocks and Color Temperature: Getting It “Just Right:
Remember the story of Goldilocks and the Three Bears? In particular the part where Goldilocks tries each bear’s porridge, finding the first too hot, the second too cold, with the third being just right. The same thing can happen when using your microscope.
We have all captured an image that is either too blue (too cold) or one that is too yellow (too hot). Whether you are looking down the eyepieces, capturing an image, or printing one out, there is an easy way to find the “just right” image, but first you need to know a little bit about achieving the right color temperature in your microscope.
We frequently see microscope users making adjustments to the rheostat (voltage control) to either increase or reduce light intensity. While intensity is affected by changing the rheostat, making adjustments to the voltage also changes the color temperature emitted from your light source. Color temperature, measured in degrees Kelvin, is a characteristic of light and is used to specify the color of a light source. Setting the microscope voltage too high results in a higher color temperature (bluish overall, too cool) [Figure 1] or a lower color temperature (reddish-yellow overall, too hot) [Figure 2] when the voltage is too low. For microscopical observations, a standardized color temperature has been established to ensure everyone looking at and working with a sample is seeing an identically illuminated image. Industry specialists determined that 5500K is the universally standardized color temperature, and maintaining 5500K (by keeping your ‘paws’ off of the rheostat) will prevent different interpretations of absorption colors, pleochroic colors, dispersion staining colors, retardation colors, and reflection colors [Figure 3].
Microscopists appreciate that to achieve analytical results that are repeatable and universally recognized, the light source must be kept at a standard daylight color temperature (5500K).
Making it “just right”
To help get a color temperature that is “just right” consider these points. Maintain a constant 5500K by operating your microscope at the voltage prescribed by the bulb manufacturer. This will help ensure that your observations are accurate and reproducible. Insert the appropriate blue filter to convert your tungsten or halogen lamp from its 3200K or 3400K to 5500K, and the appropriate neutral density filter to establish a comfortable level of light intensity. With these simple steps your analyses will be repeatable and the light intensity and color temperature will be “just right”.