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Can two equally bright lights deliver different energy per photon?
Wavelength and brightness describe different parts of a light beam.
Sources for this view
For light in vacuum, each photon carries E = hc/λ. Shorter wavelength means greater energy per photon; increasing the number of photons increases the total energy without changing the energy of each one.
Sources for this view
Explore the model (optional)
EXPLORE THE MODEL
Photon energy and an ideal threshold
E = hc/λ; λthreshold = hc/Eg
Read sampled numerical values
| Vacuum wavelength (nm) | Photon energy | Assumed band gap |
|---|---|---|
| 350 | 3.542 | 1.12 |
| 480 | 2.583 | 1.12 |
| 610 | 2.033 | 1.12 |
| 740 | 1.675 | 1.12 |
| 870 | 1.425 | 1.12 |
| 1,000 | 1.24 | 1.12 |
| 1,130 | 1.097 | 1.12 |
| 1,260 | 0.984 | 1.12 |
| 1,390 | 0.892 | 1.12 |
| 1,520 | 0.816 | 1.12 |
| 1,650 | 0.751 | 1.12 |
| 1,700 | 0.729 | 1.12 |
A photon at or above the chosen band gap satisfies the simple energy comparison. That does not mean every such photon is absorbed or collected as a useful electrical signal.
What this model can establish
An assumed band gap is a threshold, not a complete absorption or detection model. Silicon has an indirect gap; phonons, thickness, reflection, carrier collection and noise matter.
Optional: check your understanding
MAKE THE CONNECTION
A beam keeps its wavelength but doubles its photon rate. What doubles?