Photometer and gas lamp: what they have in common

1. Step 1. Photometer — uses — Reflection of light. Brightness is judged from reflected light.
2. Step 2. Reflection of light — is used in — Otoscope. A small mirror directs the light.
3. Step 3. Otoscope — has part — LED. Illumination.
4. Step 4. LED — is part of — Street light. LEDs.
5. Step 5. Street light — evolved from — Gas lamp. Gas lamps.

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