SAE Class for Vehicle Safety Warning Lights

What is the difference between SAE Class 1, SAE Class 2 and SAE Class 3 Warning Lights?

SAE Class 1 Warning Lights
SAE Class 1 Warning Lights are most often used for emergency response vehicles such as police, fire and ambulance. Lights in this class have a candela value greater than 8100, with some reaching close to 18,000 cd-s/m when used to clear traffic in emergencies. SAE Class 1 lights are 4 times more intense than SAE Class 2 lights and 10 times more intense than SAE Class 3 lights. 

SAE Class 2 Warning Lights
SAE Class 2 Warning Lights are commonly used on utility and service vehicles moving at or below the speed of traffic. Candela values in this class range from 1981 cd to 8099 cd-s/m. Vehicles that are slow-moving or blocking traffic typically have warning lights with a candela value close to 4,500. SAE Class 2 lights are approximately 2.5 times as bright as SAE Class 3 lights.

SAE Class 3 Warning Lights
Because SAE Class 3 Warning Lights have the lowest light intensity of the three SAE classes, they are typically used inside of buildings where there is little or no ambient sunlight. Class 3 warning lamps may be used on forklifts, specialized machinery, or for an attention-grabbing effect at trade shows and indoor events.