How many nox is 1 phot?

1 phot equals exactly 10,000,000 nox. The phot equals 10,000 lux, and one lux equals 1,000 nox, so 10,000 × 1,000 = 10,000,000 nox.

The nox (symbol nx) is a unit of illuminance equal to 0.001 lux (one milli-lux). It was introduced for measuring very low light levels such as moonless nights or twilight conditions. It is not part of the SI system but is used in some photometric and visibility standards.

The phot (symbol ph) is the CGS unit of illuminance. It equals one lumen per square centimeter, which is 10,000 lux. It was widely used before the SI system adopted lux as the standard illuminance unit.

What is the formula to convert phot to nox?

nox = phot × 10,000,000. This comes from the two-step conversion: phot → lux (multiply by 10,000) then lux → nox (multiply by 1,000).

How do phot, lux, and nox relate?

1 ph = 10,000 lx = 10,000,000 nx. All three measure illuminance (lumens per unit area) but use different scales. Lux is the SI standard; phot is CGS (very bright scale); nox is a low-light milli-lux scale.

Phot to Nox Converter

Enter a phot value and instantly get the equivalent in nox, plus the step-by-step formula and common lighting reference points.

Phot to Nox

Illuminance in phot (ph)

Enter a phot value above to see the result.

Formula: nx = ph × 10,000,000 (1 ph = 10,000 lx; 1 lx = 1,000 nx)

Common Lighting Levels

Environment	Phot (ph)	Nox (nx)

Click any row to load that phot value into the converter.

Summary

This converter turns any phot value into nox in real time. The phot (ph) is the CGS unit of illuminance equal to one lumen per square centimeter, or 10,000 lux. The nox (nx) is a low-light illuminance unit equal to 0.001 lux, used for measuring very dim environments. Because 1 ph = 10,000 lux and 1 nx = 0.001 lux, the conversion factor is exactly 10,000,000 nox per phot. All math runs in your browser with no server call needed.

How it works

Enter the illuminance value in phot in the input field.
The converter first converts phot to lux by multiplying by 10,000.
It then converts lux to nox by multiplying by 1,000 (since 1 lux = 1,000 nox).
The combined factor is 10,000,000: nox = ph × 10,000,000.
The result updates instantly as you type.
Click Copy to copy the nox result to your clipboard.

Use cases

Convert CGS phot measurements to nox for low-light photometric analysis.
Interpret historical illuminance data from CGS-based scientific papers in nox.
Cross-check illuminance unit conversions between CGS and low-light standards.
Translate legacy optical engineering values for modern photometric work.
Verify conversion factors when working across multiple illuminance unit systems.
Compare phot-scale lighting values against nox-scale night-time measurements.

Frequently Asked Questions

Last updated: 2026-09-09 · Reviewed by Nham Vu