The effect of light on reaction time

Taylor Augustine and Ben Chandler

CU Boulder, Fall 2008


            Our experiment analyzed how varying intensity of artificial light affects visual reaction time.  Through basic evolutionary study, one learns that the human eye is not accustomed to crisp vision in darker atmospheres.  Since humansŐ eyes are not easily adjusted to the dark, we hypothesized that reaction times will be dependent on the intensity of artificial light in the setting.  Knowing that humans do not possess a nocturnal feature, we believed the reaction times in the dark would be slowest and progress proportionally as light intensity increased.     

            Subjects, one male and one female, were 19 years of age and healthy.  The female subject, however, wore soft contact lenses for myopia.  Each underwent ten trials under each light setting: bright artificial light, dim artificial light, and darkness.  Appropriate intensity of light to fit into these specified categories was qualitatively assessed.  Two to three minutes of adjustment time was allowed before testing began.  Reaction time was measured in seconds with a brain physiological reaction timer.  The tests were performed in response to different color lights flashing, randomly selected by reaction time operator.

            The data contradicted our prediction.  It showed mean reaction time as slowest in the bright artificial light, then the dark, and quickest in dim artificial light at 0.5388 sec, 0.4974 sec, and 0.4966 sec respectively (bright v dim P<0.402, bright v dark P<0.353, dim v dark P<0.984).  

            These results are thus inconsistent with the previously stated hypothesis.  Many factors may have affected the experiment, including the level of background noise occurring in each setting.  During the bright artificial light trials there were noticeably more distractions in the setting than for the dim artificial light and dark trials.  We could have resolved such a predicament by experimenting within the same room, either quiet or noisy, and modifying the lighting to said specifications.  The subjects were very different: opposite sexes, one with good eye health, and the other with a vision hindrance. 

            Rectifying these variances involves a wider pool of subjects fitting into a more specific set of criteria.  This would later allow us to compare between the categories of people.  Reinberg et al. (2002) addresses such differences within his study of reaction time to light signals stating that age and gender significantly affect reaction time.  Incorporating a similar light sensitivity aspect to our study, R.A. Patzner (1978) analyzed light sensitivity concluding that species accustomed to darker atmospheres experienced significantly quicker reactions to light than those inhabiting a well lit environment.  His subjects, however, were fish- which causes an indirect comparison of data, though the principle may still be applied.  The discrepancies discovered in our experiment raised new questions and curiosity for future study.  Because humans are accustomed to living in a bright, artificially-lit environment, their light sensitivity within such a setting is slower than when placed in a dim light atmosphere.  This could explain why our data shows the slowest reaction times when tested in a bright, artificially-lit setting and the quickest reaction times in a dim setting.   


Reinberg, Alain; Bicakova-Rocher, Alena; Mechkouri, Mohamed; Ashkenazi, Israel. Right- and left-brain hemisphere. Rhythm in reaction time to light signals is task-load-dependent: age, gender, and handgrip strength rhythm comparisons. Chronobiology international. 2002 Nov, 19(6):1087-106. 


Patzner, R.A. Experimental studies on the light sense in the hagfish. Helgoland Marine Research. 1978, April, Volume 31, Numbers 1-2: pg 180-190.