Today’s Question: This may be very basic, but I’ve never understood why I need to see a flashing light on my camera indicating that photos are being written to the card. What benefit does that knowledge provide?
Tim’s Quick Answer: The light you’re referring to indicates that data is being written to the media card in the camera, which serves as a reminder not to eject the card or otherwise interrupt the process of writing data. Interrupting that process can cause files (photos and videos) to be corrupted or lost.
More Detail: When you capture a photo or video on a digital camera, the resulting file does not appear instantly on the media card in the camera. While the file can generally be written to the card very quickly, sometimes a little extra time is involved.
For example, when you capture a burst of photos, the image data is first stored in a memory buffer in the camera, and then written out to the media card. If you have captured a large burst of photos it can take considerable time to write all of the files to the media card, especially if the media card you’re using isn’t particularly fast.
During the time that data is being written to a media card, it is very important not to interrupt that process. If, for example, you capture a burst of ten photos and then immediately remove the media card from the camera, you would likely find that most of the image files never made it to the media card, and those that did may very well be corrupted.
So, the flashing light on your camera that indicates data is being written to the card is really a warning not to interrupt that process.
Many (if not most) digital cameras today will continue writing data to the media card even if you turn off the camera. You may have noticed, for example, that even after turning off the camera the flashing light continues to flash. However, if you remove the media card from the camera (or in most cases even open the battery door or the media card access door) you will interrupt the process of writing data to the card, and data may become corrupted or lost.