The traditional light source for studying lenses and mirrors is either a bare white light bulb,1 or one encased inside a lamphouse.2, 3 A simple pattern like an arrow, mounted on an optical bench or printed on the window of a lamphouse, serves as the object. Ironically, the image captured on a translucent screen is often the shadow of the pattern with no light falling on it. Although LEDs have been used in commercial display boards for decades, the advantage of using LEDs as a multipurpose light source in the physics laboratory has been overlooked by many physics teachers. In this paper, we remind readers of a few examples of how LEDs can be used to replace the incandescent lamp for geometrical optics, physical optics, and fiber optics experiments.

1.
Carolina Science and Math Catalogue, Item code ER-75-5074 (USA, 2003), p. 840.
2.
PHYWE 2000 Catalogue, Item code 11601 (Germany), p. 282.
3.
Philip Harris International 2001 Cataogue, Item code A45913 (U.K.), p. 368.
4.
At this setting, the operating voltage and current of each LED is v = 1.75 ± 0.05 V and i = 12.5 ± 2.5 mA, respectively. The variation is mainly due to the change in internal resistance of the battery.
5.
Se-yuen
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Using infrared emitting diodes
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