Photodiode and greenhouse: what they have in common

1. Step 1. Photodiode — is part of — Pulse oximeter. A photodiode.
2. Step 2. Pulse oximeter — uses — Infrared radiation. Infrared absorption by haemoglobin.
3. Step 3. Infrared radiation — is used in — Greenhouse effect. Infrared radiation is trapped.
4. Step 4. Greenhouse effect — is used in — Greenhouse. Glass lets light in and holds heat.

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