Photography itself is built on photochemistry, because it relies on chemical changes caused by light exposure.
Role of Photochemistry in Photography
- Light Absorption
- In traditional (film-based) photography, the film is coated with light-sensitive compounds, mainly silver halides (like AgBr or AgCl).
- When light falls on these compounds, photochemical reactions start.
- Formation of a Latent Image
- Photons from light strike the silver halide crystals, freeing electrons.
- These electrons reduce Ag⁺ ions to metallic silver (Ag⁰).
- This creates a tiny, invisible pattern on the film called the latent image.
- Development Process
- During chemical development, special reducing agents convert the exposed silver halides into visible metallic silver.
- Unexposed crystals remain unchanged.
- Fixing the Image
- The film is treated with a “fixer” (like sodium thiosulfate), which removes the unexposed silver halides.
- This prevents further reaction with light, making the image permanent.
- Color Photography
- Uses layers of different light-sensitive dyes along with silver halides.
- Photochemical reactions in each layer respond to red, green, and blue light separately, producing a full-color image after processing.
- Digital Photography (Modern Context)
- Even though digital cameras don’t use silver halides, photochemistry inspired sensor design.
- Light is still absorbed and converted — not into chemical changes, but into electrical signals in photodiodes.
Example in Action:
- In black-and-white film:
- Bright areas expose more silver halide → more metallic silver forms → darker regions in the final photo.
- Dark areas expose less silver halide → remain lighter.
In short: Photochemistry is the science that makes photography possible — turning light into chemical changes that form and preserve images.