'Air pressure, humidity, radiation densities, atmosphere, chemistry, temperatures, cultural conditions - those things are all simple.

Thus the observed radiation density (the sky brightness of extragalactic background light) can be independent of finiteness of the Universe.

The rate at which stimulated emission occurs is proportional to the number of atoms N in the excited state, and the radiation density of the light.

A related constant is the radiation constant (or radiation density constant) a which is given by:

Measured radiation densities per kilogram reached 250 becquerels in eastern Hokkaido, and 25 becquerels in the mountains of western Japan.

The screens sputtered with ionization; if it weren't for the Drive field's shielding effect, Lisele knew, they d all be fried by now, from sheer radiation density.

Given an antenna's power density , radiation density is calculated by multiplying it with the square of the distance () from the antenna to the designated solid angle:

Therefore, when the numbers of atoms in the ground and excited states are equal, the rate of stimulated emission is equal to the rate of absorption for a given radiation density.

The radiation density had a major impact on various physical processes in the early Universe, leaving potentially detectable imprints on measurable quantities, thus allowing us to infer the value of N from observations.

Even though the matter energy density surpassed the radiation density at this point, the universe remained optically thick to radiation until a cosmological redshift of approximately 1100, when the universe was about 378,000 years old.

In these models, the quintessence field has a density which closely tracks (but is less than) the radiation density until matter-radiation equality, which triggers quintessence to start having characteristics similar to dark energy, eventually dominating the universe.

Here is the radiation density today (i.e. when ), is the matter (dark plus baryonic) density today, is the "spatial curvature density" today, and is the cosmological constant or vacuum density today.