Why laser light is much more dangerous to your eyes than...

A 60 W lightbulb emits light in all directions, so that the light propagates as a sphere with an ever-increasing radius. A 600 mW laser emits light in only one direction, so that the light propagates as a cylindrical beam whose circular cross-section remains (relatively) constant with a diameter of 1 mm. Notice that the lightbulb outputs 600 times the power of the laser! But a device's output power is not what is hazardous to your vision. Instead, a vision hazard occurs when too much intensity hits your eye. A. Consider first the case where you place your eye very close to the lightbulb, say 10 cm away from the center of the bulb; what light intensity from the bulb hits your eye? B. Now consider the case where you stand back 5 m from a laser and allow its beam to shine directly into your eye; what intensity of light from the laser hits your eye? C. What is the ratio of laser intensity vs. bulb intensity that hits your eye?

Penny R.