Simultaneous Brightness Contrast, explained.
Simultaneous brightness contrast is a context effect in which identical patches can appear different in brightness against different surrounds.
Why it happens
The reference patch has RGB channels 128. The comparison patch is adjustable from 64 to 192. Equalising surrounds leaves patch values unchanged so appearance and drawing values can be compared.
Simultaneous brightness contrast is a context effect in which identical patches can appear different in brightness against different surrounds.
Read the result
Compare RGB channels only as drawing specifications. Their difference is not a measured luminance difference.
A worked example
Two patches on different surrounds
Adjust the right patch until it appears to match the left patch on your display.
Equalise the backgrounds without changing either inner square’s channel values.
Compare the recorded values with the appearance and keep the uncontrolled screen conditions in mind.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
The reference patch has RGB channels 128. The comparison patch is adjustable from 64 to 192. Equalising surrounds leaves patch values unchanged so appearance and drawing values can be compared.
Where this idea is useful
A practical use
Choose readable interface colours by testing them against their actual backgrounds, rather than viewing isolated swatches.
A common misconception
“Equal RGB guarantees equal appearance in every context.”
RGB specifies input values. Perceived brightness depends on context and display conditions as well as those values.
What this explanation leaves out
- RGB channels are not calibrated luminance; display settings and ambient illumination are uncontrolled.
Does this calibrate my monitor?
No. There is no physical luminance measurement, standard viewing environment or validated calibration procedure in this activity.
Have you tested a colour against every background where it will be used?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.