The nox (nx) is a non-SI unit of illuminance equal to 0.001 lux (one millilux). It was introduced to express very dim light levels — such as starlight — without writing inconveniently small decimal fractions of lux. It is rarely used outside specialist photometry.

The phot (ph) is the CGS (centimeter-gram-second) unit of illuminance. It equals one lumen per square centimeter, which is 10,000 lux. The phot was common in scientific literature before the SI system standardized on lux.

How do you convert nox to phot?

Divide the nox value by 10,000,000. For example, 10,000,000 nox = 1 phot. The two-step path is: nox ÷ 1,000 = lux, then lux ÷ 10,000 = phot.

How many nox is 1 phot?

1 phot equals exactly 10,000,000 nox. This comes from 1 phot = 10,000 lux and 1 lux = 1,000 nox, so 1 phot = 10,000 × 1,000 = 10,000,000 nox.

Why would anyone need this conversion?

Nox describes extremely dim conditions (sub-lux) while phot is an older CGS unit for potentially bright settings. Comparing values across these two systems appears in historical photometry research, night-vision optics, and academic papers that combine CGS and non-SI units from different eras.

Are nox and phot still in common use?

Neither unit is part of the modern SI system. Lux is the current standard. The nox appears in older astronomical and environmental studies; the phot appears in pre-SI CGS scientific literature. You may encounter both when reading vintage photometry references.

Nox to Phot Converter

Enter a nox value and instantly get the equivalent in phot, plus the two-step formula and a dim-light reference table.

Nox to Phot

Illuminance in nox (nx)

Enter a nox value above to see the result.

Formula: ph = nx ÷ 10,000,000 | 1 nox = 0.001 lx | 1 ph = 10,000 lx

Reference Levels

Environment	Nox (nx)	Phot (ph)

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

Summary

This converter turns any nox value into phot in real time using the exact factor: 1 phot = 10,000,000 nox. The nox equals 0.001 lux, while the phot (CGS) equals 10,000 lux, so bridging these two units requires dividing by 10 million. All math runs in your browser with no server call. A reference table of typical dim-light environments lets you put results in practical context.

How it works

Enter the illuminance value in nox in the input field.
The converter first converts nox to lux by dividing by 1,000.
It then converts lux to phot by dividing by 10,000.
The combined factor is 10,000,000 — the result updates instantly as you type.
Copy the result with one click.
Use the reference table to compare your result against common dim-light environments.

Use cases

Compare starlight or moonlight readings expressed in nox with CGS photometric data in phot.
Bridge historical dim-light photometry (nox) with older CGS-system references (phot).
Convert night-sky quality survey data for use in CGS-based optical engineering documents.
Validate illuminance chain calculations that pass through both nox and phot values.
Cross-check academic references that mix the nox and phot units in the same dataset.
Translate very low-light sensor readings into phot for legacy CGS instrument calibration sheets.

Frequently Asked Questions

Last updated: 2026-07-14 · Reviewed by Nham Vu