above is for Hawking's surface gravity modes - low energy.
This is ~ 10^-28 Watts per solar mass isotropic over 4pi solid angle
i.e. P ~ 1/A
A is area-entropy of the black hole horizon
For the new quantum thickness radiation we are now predicting.
P' ~ 1/(LA^1/2)
P'/P = [1/(LA^1/2)]/[1/A] = A/(LA^1/2) = A^1/2/L
P' ~ (A^1/2/L)10^-28 Watts per solar mass
Let r = distance of black hole from Earth (neglecting intervening curvature for simplicity)
The power flux density at Earth is then
P'/4pir^2 ~ (A^1/2/4pir^2L)10^-28 Watts per solar mass per unit area
There is a spectrum of L's.
If L = Lp that is from virtual Planck scale black holes of Wheeler's quantum foam getting energy from the gravity near field emitting spin 2 gravitons. For example, I get ~ 10^-6 gravitons of ~ 10^21 Hz per square meter per second hitting Earth from the 4 million solar mass black hole at the center of our Milky Way. Too small to measure most likely even though it's much larger than the flux from Hawking's surface modes.
On the other hand if L = h/mc ~ 10^-11 cm these are virtual electron positron pairs getting energy from the gravity near field and the charges that escape the horizon accelerate emitting photons.
Similarly L ~ 10^-13 cm will be radiation from virtual nucleon pairs etc.
However, clearly the HFGW mechanism at L = Lp dominates.