science

Phot

Phot is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Phot rather than just read about it. In short: A phot (ph) is a photometric unit of illuminance, or luminous flux through an area. It is not an SI unit but rather is associated with the older centimetre–gram–second system of units.

Key takeaways

Phot belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Phot to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Phot from memory before moving on to harder problems.

Reference excerpt

A phot (ph) is a photometric unit of illuminance, or luminous flux through an area. It is not an SI unit but rather is associated with the older centimetre–gram–second system of units. The name was coined by André Blondel in 1921. Metric equivalence:

1 p h o t = 1 l u m e n c e n t i m e t r e 2 = 10 , 000 l u m e n s m e t r e 2 = 10 , 000 l u x = 10 k i l o l u x {\displaystyle 1\ \mathrm {phot} =1\ {\frac {\mathrm {lumen} }{\mathrm {centimetre} ^{2}}}=10,000\ {\frac {\mathrm {lumens} }{\mathrm {metre} ^{2}}}=10,000\ \mathrm {lux} =10\ \mathrm {kilolux} }

Metric dimensions:

Illuminance = luminous intensity × solid angle / length2

See also Illuminance Lumen (unit) Lux Photometry (optics) Light

References

External links Knowledgedoor, LLC (2005). Library of Units and Constants: Illuminance Quantity. Retrieved 2006-07-21. Illuminance Converter. Retrieved 2006-07-21.

Worked examples

Example 1 — a first encounter with Phot

Start with the simplest possible case. Write down what Phot claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Phot before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Phot ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Phot

In research: Phot appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Phot in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Phot is common in secondary-school and first-year university syllabi. It links to neighbouring topics Centimetre–gram–second system of units, Units of illuminance, so understanding it makes those chapters shorter.
In everyday life: Look for Phot outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Phot in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Phot means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Phot out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Phot in simple terms?

A phot (ph) is a photometric unit of illuminance, or luminous flux through an area. It is not an SI unit but rather is associated with the older centimetre–gram–second system of units.

Why does Phot matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Phot?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Phot.