Then one might try to estimate it from the apparent reflector surface, because CP directly depend on this value.
Everything else might be sufficiently similar, carbon arc, rhodium plated mirror, glass lens.
Edit:
except that it' doesn't seem to be a carbon arc! Why did I take this for granted without thinking twice? I admit I love carbon arcs...
This book reads as if it had an incandescent light?
I leave my original post unchanged below. I just insert here my idea about an 18" incandescent light:
AFAIK, these sources have 20-30cd/mm². So it looks rather like 20 or 30 multiplied with (14"/2)²*pi*0.85*0.92 = 1.56...2.33 Mcd
And if it was even less than 20cd/mm² then it's more than difficult.
The original question, wondering about 1 Mcd in particular, seems to have some more vague knowledge?
Original continued:
The GE 60" seems to have an effective mirror diameter of about 53" (7" less).
Let's assume the 18" M46 has an actual diameter of 14" (4" less).
Let's ignore the central shadowing, it's a small area in relation.
The relation of CandlePowers then would be that of the mirror surfaces, that is, 14² / 53² = 7%.
The GE 60" is said to have 800 MCd, so the M4 might have had 56 Mcd (rough estimation only).
The carbon arc certainly might be different, but if you bother to build an 18" light, you will manage not be way too far off...
I think it's safe to assume at least this magnitude of CP, i.e., 40-60 Mcd.
By the way, this also asks for calculating the luminance of such a 60" carbon arc.
- rhodium reflectance is about 80%
- the front glass lens transmission is about 92%
- the central shading by the baffle near the arc seems to be almost 8" diameter (estimated from pictures)
That's an actual apparent mirror area of about 1,390,000 mm² (sorry for switching metrics
.
Thus, the light has an apparent luminance of 575 cd/mm².
For the very carbon arc: add the transmission losses, so it's 575/0.92/0.80 = 780 cd/mm²
I searched for literature values and found "Handbook Of Optics, Artificial Sources, A.LaRocca" which mentions 650cd/mm² for search lights (no specific model given, 16mm electrode, 150A, 78V) and 960cd/mm² (for movie theatre projectors, 13.6mm electrode, 160A, 66V).
That's hell of a lot, given that the carbon arc has a diameter of roughly an inch.
Xenon lamps range from about 400 to 3000 cd/mm², but only at a few mm² at best, and just fractions of mm² for the maximum values.
Automotive HIDs have about 60-90 cd/mm² (average value, the electrode hot spots are higher but usually not of concern).
