VS - Lighting Systems - Lighting - 998542

5. The lighting system: what is light?

5.3. Photometric basics Photometry is the science concerned with measuring human visual response to light, here are a few basics that are good to know prior to jumping into the lighting systems.

I (cd)

5.3.1. Light intensity

The intensity is the luminous energy from a lighting source in a specific direction:

Intensity versus angular viewing

180°

150°

l Symbol: I l Unit: Candela (cd)

120°

20 40 60 80 60 40 20 80

Light intensity varies depending on which direction the light source is being viewed from. This figure below illustrates a light source emission profile; it can be seen how intensity drops from 140 cd@20° (front viewing) to 70 cd@90° (side viewing).

cd

MIN.

90°

Some examples of Candela intensity on automotive lighting systems:

60°

l A candle: 1 cd (reference) l Parking lights: 2cd l Position lights: 4 cd l Direction lights: 50 cd l Stop lights: 60 cd l Reversing lights: 80 cd l Fog lights: 150 cd l Daytime Running Lights: 500 cd l Low/High beams >1000 cd

100 120 140

MAX.

0°

30°

12