Can you help me with my experiments into the effect of different colourerd lights on the germination and growth of cress seeds?
This is really a very open-ended investigation. In order to compare your results with anyone else's, we would need to know a huge amount of information - like the details of the exact filters you are using to produce your coloured lights.
However, far more important is the fact that this is a genuine investigation on your part and the results you get will be the answer to the question with relation to YOUR seeds and YOUR filters in YOUR laboratory.
So long as you collect numerical data (lengths of roots, number of seeds germinated, lengths of shoots etc) you will have data which you can tabulate, plot on graphs, carry out statistical analysis and generally show that you know HOW to carry out a scientific investigation, which is what the exercise is all about at A level.
Two things are changing in your experiments. First, the QUANTITY of light getting to each treatment - each filter will let through a different amount of light. Secondly, the colour of the light - filters do not let through light of only ONE wavelength, but a spread of wavelengths centred around the colour they appear to be. Then you have to consider whether the seed/seedling is able to ABSORB the colour of light you are exposing it to eg. leaves are green because they do not absorb much green light.
Student Sheet 8 on our site may offer a suitable protocol for this investigation.