The adjective cumulative describes the total amount of something when it's all added together. Eating a single chocolate doughnut is fine, but the cumulative effect of eating them all day is that you'll probably feel sick. If something is cumulative, it is heaped together so it can be counted up to get a total number. The cumulative snowfall for the whole winter isn't just the amount of snow that fell in one month, but rather the number of inches that fell every month that winter to get the total, cumulative, amount.
Light has a constant speed through a given substance. For example, it always travels at a speed of approximately 3 x 10 8 metres per second in a vacuum. This is actually the speed that all electromagnetic radiation travels-not just visible light.
Radiation originating in a varying electromagnetic field, such as visible light, radio waves, x-rays, and gamma rays. electromagnetic radiation. Energy in the form of transverse magnetic and electric waves. In a vacuum, these waves travel at the speed of light (which is itself a form of electromagnetic radiation). The acceleration of electric charges (such as alternating current in a radio transmitter) gives rise to electromagnetic radiation.