dadiOH wrote:

Don Wiss wrote:

I have a skylight shaft that I've like to maximize the light coming down...

Remember the foil reflecting material used over car dashes? Use that or
similar for max reflectance. However, max reflectance may not give you the
max output at the bottom because they are so directional.

Not according to the usual lightwell calculations.

Think of a mirror...you have to angle it around to reflect the source light
where you want it to go. For your purpose, a non specular (not glossy)
white or aluminum paint would probably be best due to the usual shape of
a skylight shaft.

I doubt that. Can you find a specific example that makes your claim true?

Nick

10 RHO=.9'lightwell wall reflectance
20 W=4'lightwell width (feet)
30 L=8'lightwell length (feet)
40 C=4'concentration factor
50 EC=.8'concentrator efficiency
60 TFLUX=8000*W*L*C*EC'total flux entering well (FC)
70 FOR F = 1 TO 8'floor number
80 H=8*(8-F)'lightwell depth (feet)
90 R=5*H*(W+L)/(W*L)'well cavity ratio
100 E=EXP(-.0443*R/RHO)'transmission
105 PRINT F,E
110 ATTN=ATTN+1/E'cumulative attenuation
120 NEXT
130 ATA=ATTN/8'average attenuation
140 PRINT ATA'average attenuation
150 AREA=32^2*8'floor area (ft^2)
160 ER=.9'secondary reflector efficiency
170 PRINT ER*TFLUX/ATTN/AREA
180 ER=.6'eg 2 wall bounces, and a bottom reflection...
190 PRINT ER*TFLUX/AREA

Floor Lightwell
number Transmittance

1 .0056940
2 .0119144
3 .0249304
4 .0521655
5 .1091535
6 .2283978
7 .4779098
8 1

Average diffuse well attenuation: 41.9

Illumination from diffuse well: .268 footcandles

Illumination from mirror well: 60.0 footcandles(?)

Nick