How to Change Your Microscope’s Halogen Bulb

If you have a microscope that uses halogen bulbs you will eventually need to change the bulb. While it seems like an easy thing to do, I’ve seen more than my share of bulb-changing mistakes. Help eliminate down-time and microscope issues by following these easy steps:

  1. Make sure the bulb is actually bad
    • Sounds like an obvious step, right? Every now and then the bulb not lighting can be something as simple as the power cord getting accidentally unplugged. Or a power strip turned off. Or a blown breaker. Or… the possibilities are endless.
  2. Remove the bad bulb
    • The location of the bulb will depend upon which microscope model you have. Most bulbs are located at the rear of the microscope. Some are located on the bottom or side of the microscope. It’s usually obvious to see the lamp assembly. If in doubt, look at your microscope’s user manual.
    • Because the bulb can get extremely hot and bright, there will be a cover or shield that hides the bulb. Remove the cover/shield. You should now see the bulb. Pull the bulb straight out, being careful not to damage the socket.
  3. Install the new bulb
    • Make sure the new bulb is really new. Seriously. For some reason people save their old, burnt out bulbs. I regularly get calls for bulbs not working right after a “new” bulb was installed. Almost always (8 times out of 10) the bulbs are actually not new, but previously removed. Go figure…
    • Make sure the new bulb is the correct voltage and wattage. These are usually printed on your microscope’s label or lamp housing. If not, it is printed on the glass bulb just above the pins.
    • Always be careful NOT to touch the new bulb with your bare hands. The oils from your skin can damage the bulb and shorten it’s life. If you do accidentally touch the bulb with your bare hands, you can wipe it off using isopropyl alcohol (IPA).
    • Halogen bulbs will usually be in a sealed plastic enclosure. Gently tear the bottom edge of the enclosure closest to the bulb’s pins. Allow the pins to stick out of the enclosure.
    • Be sure that the bulb’s pins are aligned with the socket’s holes. Gently push the bulb into the socket assembly. Be sure to insert the bulb completely into the socket. Verify the bulb is straight up and down, not crooked.
    • Reinstall the cover/shield.
  4. Align the new bulb, if adjustable
    • Some microscopes give you the ability to center the bulb for maximum efficiency. If your microscope does, please follow the user guide to correctly align your bulb. It is critical to do this correctly as uneven lighting decreases your ability to accurately view samples on your microscope.
    • If your microscope isn’t adjustable, then you are finished with the bulb replacement.
  5. Power on microscope and verify proper operation.
    • If the lamp comes on and everything looks good, congratulations! You are finished.
    • If the lamp doesn’t come on, verify the bulb is actually new (remember Step 3a above?). If you still have no light after checking everything, you will want to call a qualified microscope maintenance professional. You could have a bad socket, fuse or power supply.

Hope this helps! If you have any questions or comments please contact us.

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How to Adjust Kohler Illumination

Having improperly adjusted Kohler Illumination can cause uneven illumination and poor resolution of your specimen. Adjusting the Kohler Illumination is quick and easy. Just follow the steps listed below.

  1. Focus the Condenser
    • Place a slide on the stage and focus on it using the 4x or 10x objective.
    • While looking through the eyepieces close the Field Diaphragm until you see the edges of the Diaphragm come into view.
    • Move the condenser up or down until the edges of the Field Diaphragm come into focus.
  2. Center the Condenser
    • Located on the condenser arm are two adjusting screws used for centering the condenser. Turn the screws to center the edges of the Field Diaphragm. Note: It is easier to do this if you adjust the Field Diaphragm so the edges of the circle are almost to the edge of your field of view.
    • Once the condenser has been focused and centered the Field Diaphragm should be opened so that it is just outside the field of view. The condenser will remain centered when different objectives are selected.
  3. Adjust the Aperture Diaphragm
    • The Aperture Diaphragm is located on the condenser assembly. With the condenser focused and centered the Aperture Diaphragm should be adjusted so that your specimen isn’t bleached out with too much light or so dark that the resolution is too low to see the finer details. To adjust the Aperture Diaphragm, slide the lever protruding from the from of the condenser to the desired position.
    • The most accurate way of adjusting the Aperture Diaphragm is to note the numerical aperture (or NA) on the objective, then set the NA on the condenser to 20% less. Although some specimens may need variation on the 20%, beware of closing the iris too much as resolution will be drastically reduced.
    • Another method is the “fly by the seat of your pants” method. Adjust the Aperture Diaphragm so your specimen looks best for your needs. Your lighting, slides, specimen samples and the quality of your microscope’s optics will differ from everybody else. All microscopes are different. Settings that work best on one microscope may not work well on another. You will quickly learn where to set everything once you’ve done the adjustments a few times.

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