If we go to a bright room after sitting in dark room there our eyes wont open properly because ciliary muscle should be adjusted it takes some time to adjust
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This phenomenon is called adaptation of eye.  Our eye senses a wide range of intensity of light.  The range is 1 billion times from faintest light rays from distant stars to the Sun light on the brightest day.

It can take about 5 minutes to adjust to darkness coming from full brightness. To fully adjust and to be able to see in darkness very well, it will take 20 minutes.

Our eye adjusts itself so that the intensity of light falling on the retina is with in an acceptable range.  The pupil in the front of the eye can change in diameter from 1mm to 8 mm in total darkness.   It takes the pupil to do so.  There are other reasons also.

The eye (retina) has light sensors - photo receptor cells, which are special neuron cells in the retina.  They convert light into biological neural signals. These are two types mainly:  Rods and cones.   Rods work at very faint light intensities.  Cones and rods both work in bright light.
   Rhodopsin is the biological pigment present in rods and cones. It photobleaches (destructively) on receving light (photons).  As light falls on retina they get photobleached and newer pigments are generated.   Rods take a longer time to regenerate the Rhodopsins to continue visualization and hence they take a lot of time to adjust to the intensity of light.

   The cones are relatively faster but still take 5 to 10 minutes to adjust to the light.
   These generate electrical signals of range 10s of millivolts on the reception of photons. They have to adjust to different light conditions to generate appropriate voltage pulses.

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aim : to show that the eye takes from 10 min up to 20 min for adjustment, when going from dark region to bright region. Also vice versa.
when man enters darkness coming from bright light, the 3-Dimensional perception is lost.. Also colour perception (recognition) is reduced. Because, only one photoreceptor cell Rods work in darkness. Because we do not have 3D perception, we cannot climbs steps without support. U have seen this occurring in cinema theatres, when u go inside after movie starts.
you can have a color chart or color ful book for testing. a person can be asked to climb steps. for example. we can measure change in perception after every 2 minutes or 1 min. if you have a small torch light, ou can see the pupil size, in darkness and in light. you can include that in the aim also.
thanx n u r welcom