Higher Resolution Cameras Need More Light?By: John Honovich, Published on Dec 13, 2012
One of the most misleading myths is that higher resolution cameras need more light than lower resolution ones to provide quality night time video. The underlying premise behind this claim, pixel size, is a factor but one of many that impacts image performance. In this note, we share an excerpt from a distributor's catalog and break down how to best evaluate low light vs resolution:
Here's what Tri-Ed recommends:
"Lower resolution cameras have large pixels and therefore capture more light. This means they require less light to generate a usable image. Higher resolution cameras have smaller pixels that will require increasing amounts of light to provide high quality video."
However, this is too reductionistic. Let's review the many factors that come into play for low light:
- Pixel size varies even within resolution: There are SD cameras with tiny 1/5" imagers (example) to very large ones, like 1/2" imagers (example). The range is extremely significant. Even if you are focused on the imager size, make sure you check what each camera's imager size is. Many SD cameras have 1/4" imagers while increasingly HD cameras have significantly larger 1/2.7" imagers.
- F stop impact: Regardless of resolution, the F stop of the lens will have a huge impact on low light performance. Even if you have a large pixel size, using a high F number (like f/2.8) will almost certainly result in far worse low light performance than a higher resolution one with a lower f number (e.g., f/1.2). To learn more, read our f stop tutorial.
- Image processing differences: Some camera have advanced gain control or low light image processing to increase low light image details, regardless of the sensor size. For instance, this is what Axis is doing with their Lightfinder series (see our SD and HD test results). The imager is 'normal' size (1/3") but the advancement is in image processing.
- Imager Advancements: Newer imagers, almost all HD, have improved low light imaging even for the same imager size as legacy SD cameras.
For HD cameras (720p and 1080p), you will likely find similar low light performance as for SD cameras of similar specifications (form factor, lens selection, etc.), due to more advanced imagers, slightly larger imager sizes and improved image processing.
Where pixel size concern is most significant is for 5MP and greater resolution cameras. These cameras typically use the same imager size as HD cameras and, as a result, have far smaller pixels that contribute to significantly reduced low light performance. (See our MP low light shootout). However, this will not likely be the case forever. Just like early generation HD cameras had great deficiencies that were resolved over the last few years, we expect a similar path for multi-megapixel.
While pixel size is worth being aware of, overdoing its importance and not appreciating other key drivers will likely result in poor decisions.
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