What does the prefix photo- mean?
Photo- comes from the Greek phos (photos), which means "light". It shows a relation to light or to images captured with it. When you see photo-, light is always the central element.
ESEN
Prefix · light / photography
photo-
Signals relation to light or photography: photograph, photosynthesis, photon, photovoltaic.
Scientific
Written by Bryan López, English teacher · Updated
Photo- in science and technology
Beyond cameras, photo- appears in physics and biology: in the basic unit of light, in solar cells that turn light into electricity and in materials that react when exposed to it. It also forms everyday technology words. If you see photo- in a word, think of light first, not photos.
How it is used
Attaches to scientific and technical nouns and adjectives:
- photo- + process/objectgraph → photographsynthesis → photosynthesiscopy → photocopyelectric → photoelectric
- photo- + particle/energyn → photonvoltaic → photovoltaicsensitive → photosensitivetherapy → phototherapy
Pronunciation: /ˈfəʊtəʊ/.
How it is pronounced
photo-/ˈfəʊtəʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With photo-
In a phrase
- graphphotographHe took a photograph of the mountain at sunrise.
- synthesisphotosynthesisPhotosynthesis converts sunlight and water into glucose inside plants.
- nphotonA photon is the elementary particle of light with no mass.
- copyphotocopyShe made three photocopies of the signed contract.
- voltaicphotovoltaicPhotovoltaic panels on the roof generate thirty percent of their energy.
- sensitivephotosensitivePeople with lupus are often photosensitive to direct sunlight.
- therapyphototherapyPhototherapy with blue light treats jaundice in newborns safely.
Common mistakes
"photo" and "photograph" are identical in all contexts
"photo" is informal; "photograph" is the formal or technical term
In informal conversation, "photo" is the everyday short form. "Photograph" is the formal or technical form. "Photography" = the art or technique; "photographer" = the person who practises it.
photosynthesis only happens during the day
photosynthesis requires light, which can be artificial — not specifically sunlight
Plants carry out photosynthesis whenever light is available, whether solar or artificial (such as grow lamps). The absence of light stops the process, but it is the light energy itself that matters, not sunlight specifically.
A trick to remember it
Think of a camera capturing light: photo- = light. photograph, photosynthesis.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
"The solar panels use ___ cells to convert sunlight directly into electrical energy."
Exercise 3 · Pick the right one
What is the difference between "photo" and "photograph" in English?
Frequently asked questions
What does the prefix photo- mean in English?
The prefix photo- signals relation to light or photography: photograph, photosynthesis, photon, photovoltaic.
How do you pronounce photo-?
The prefix photo- is pronounced /ˈfəʊtəʊ/. For example, "photograph".
Can you give an example of a word with photo-?
"graph" becomes "photograph". It is a typical example of the photo- prefix.
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