Practical Introduction To Light

This chapter covers all the concepts at a practical level for the light emitting diode (LED) lighting engineer. Light source is measured by radiant flux. Photometric quantities are measured in 'lumens'. Photometric quantities are weighed by photopic vision, or bright light vision, as opposed to night vision, or scotopic vision. For every radiometric measure, there is an equivalent photometric measure. The chapter explains difference between luminous flux, luminous intensity, illuminance, and luminance. It compares radiated power of each light to the number of lumens. Light from an LED source depends on the particular phosphor used, and varies by manufacturer. But in general LED sources have a broader spectrum than fluorescents and will have better color rendition. The Commission Internationale de l'Eclairage (CIE) measure for color rendition is the Color Rendition Index (CRI). To find the CRI, a calculated comparison between the test light source and the reference is done with eight Munsell pastel color.