Dear Mahnoud,

I am not sure if I understand the question.However, people who are blind (cannot distinguish between light and dark) with no sight experience, simply do not understand how the light looks like and it is not necessary for their lives to function normally.  I would say that all you can do is to describe them benefits of the light for sighted people, taking into account ethical considerations. Please note that most of the students who are "blind" have some vision. 

Dear Mahnoud,

Through heat. If I remember my science is it not true that all light gives of heat? Hence, it is through heat the sightless can in-fact be taught the concept of light. For example, place the hand of a blind student flat on a table, shine a light on the hand close enough to the light they can feel some heat. Ask questions such as do you feel the heat, what about anything else such as weight, an object, ask them to explain what they feel.

Repeat this process with something cold to demonstrate the difference. This can be connected to what the person already experiences in daily life thus making the connection between darkness and cold heat and light. From this basic connection a concept of light can be formed by the sightless in comparison to as the sighted does in the dialectic between light and darkness.  From this the sky is the limit as to where you as a teacher and the blind can go if both let go of traditional structured education and let the imagination run wild.

Douglas

yes Douglas is right.First ,classify  their  levels of sight or vision impairment or challenge found in that class.:low,medium high.teach them by their experiences,You can use Douglas method to  put the pupils in different categories.then with their experience explain the concept of light. Dont forget that we teach internal organs without seeing them,something,we teach internal respiration.For the total or high level,use their imaginations rely more on their feelings.For the low and medium ,make them  understand that if light rays hit their optical nerves/retina in a more intense way,they would see better.then use their imaginations.As for HEAT,all living things are sensitive and respond negatively or positively to levels of heat in respect to their environmental conditions.So all of them can feel heat.

I hope this can help.