What is the difference between a Shuttered light source and an Instant Start light source?

Lamps in "instant start" units turn off between exposures, saving energy and reducing heat buildup. These units are typical in shops with low-to-medium production requirements. Lamps in "shuttered" units stay on all the time, but they return to standby (low output) mode between exposures. Since the lamp remains on, shutters close when the screen frame is opened in order to protect the screen from unwanted light exposure. These units are typical for high volume shops.