I need a software or an apparatus (avaiable in school conditions) to measure wavelengths of visible light. In my lab I use coloured filters to get different colours of light, but I have to measure exact wavelenths.
Before answering, please see our policy on resource recommendation questions. Please write substantial answers that detail the style, content, and prerequisites of the book, paper or other resource. Explain the nature of the resource so that readers can decide which one is best suited for them rather than relying on the opinions of others. Answers containing only a reference to a book or paper will be removed!
This depends largely on what apparatus your school already has. But every school should have a good diffraction grating and a large white screen. You can then do a diffraction experiment and take measurements on the screen. Then using the formula $d \ sin \theta =n \lambda$, you can get wavelengths. See http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/gratcal.html for more information on measuring wavelengths using a diffraction grating.
This method will probably not give you extremely precise results but should work fairly well. Do ask your school if they have any useful software for this purpose.