The higher that wattage the brighter the light - pretty simple. Light 'quality' is a little more complex since it is based on spectral output. The visible light spectrum is made up of different wavelengths or colours of light as can be seen in a rainbow. For best plant growth, the goal is to mimic sunlight as accurately as possible. The colour temperature number is used to indicate the colour of light produced by the bulb, and is based on a physics phenomena known as 'black body radiation'.
White light is composed of all colours, with each colour being of equal brightness.
The CRI indicates who well this equal balance of all colours is matched by your light source. A CRI of 100 is perfect, any number less than this and the light will still appear white, but it may make objects look bluish or reddish for example. A CRI of 70 or more is probably fine for most aquariums. The lights should be on for about 10 to 12 hours per day, and you'll need about 2 - 4 watts per gallon with a colour temperature of approximately 5000K and a CRI of 70 or better. Unfortunately, sometimes it's difficult getting a light with this kind of colour spec.