Final answer:
The need for brightness refers to 'apparent brightness,' which is the measure of light intensity received by Earth from a celestial object. It is distinct from luminosity, which is a star's total energy output. In practical terms, for light bulbs, brightness is rated in lumens and measured in candelas.
Step-by-step explanation:
The need for brightness refers to the intensity of light that an observer perceives, which is known as the apparent brightness. This is a measure of the amount of light received by Earth from a star or other celestial object. The concept of apparent brightness is important in astronomy when comparing the brightness of stars as observed from Earth. The term differs from luminosity, which is the total energy output of a star irrespective of its distance from the observer.
When comparing the brightness of light bulbs in a store, for instance, one should check the ratings in terms of lumens on the labels to determine their intensity, or brightness. The wave amplitude of light is perceived as luminous intensity, and the standard unit of intensity of light is the candela.
In summary, to understand the brightness of stars or light bulbs, it's necessary to consider apparent brightness, which is based on the energy reaching the observer, and compare this with measurements like luminosity or light bulb ratings in lumens.