[Radiance-general] low lighting? is this normal?

[Shakespeare, Robert A.]

            While other can remark on pcond and how it represents
scotopic/photopic adaptation, I would like to comment on the lighting
design issue. The close-up of the manuscript indicates a dominant
grazing highlight from the right and less contribution from the left. I
also note the shadows cast by the candle configuration.. front candles
blocking rear candles... at least that is my guess.  Consider
reorganizing the candles so that each has a full "sightline" to the
manuscript. Additionally increase the luminance of the page by moving
the candles closer and by reducing the cosine effect by repositioning.
To reduce the masking shadow cast by a reader, consider elevating the
light sources.
            Radiance provides fairly accurate representations of
lighting choices. Though there have been a few occasions where I gasped
with disbelief at a rendering of a lighting scheme I was testing, I must
acknowledge that Radiance typically illustrates the flaws and strengths
of the design choices.  
 
-Rob Shakespeare
 
-----Original Message-----
From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of John
Sutherland
Sent: Sunday, April 18, 2004 7:42 AM
To: Radiance-general at radiance-online.org
Subject: [Radiance-general] low lighting? is this normal?
 
After setting up some candles in my reconstruction using georg's advice
with the candle RGB values. I used spheres with radius 0.0075 which
worked out RGB values of
 
R=16.575
G=5.240
B=0
 
For the flames light material.( The base weightings of rgb for tallow
candle flame were R 0.759 G 0.240 B 0)
 
For a tallow candle, emitting 1 candela of light. When using these
values my night renders look like this:
 
http://homepage.ntlworld.com/mark.sutherland/internaltallow-h.jpg
 
Which is not quite what I was expecting using pcond... I get the
impression my lighting values are too low? But the results aren't too
bad, so I thought I'd try to illuminating of a manuscript.
 
In this next render I moved the candle right up close to the manuscript
(its just off the bottom), but the illumination is not really enough to
shift the book out of scotopic levels.
 
http://homepage.ntlworld.com/mark.sutherland/outputbook22hrtallow-h.jpg
 
A false colour image shows they levels barely get above 1.5 lux
 
http://homepage.ntlworld.com/mark.sutherland/outputbook22hrtallow-hfalse
color.jpg
 
I thought id try a home experiment, I lit a candle in a pitch black room
and moved a book varing distances away from the candle, and there was
very little scotopic vision even at a distance of about a metre away.
When I do a render without the candles at night the falsecolour images
show very little increase in lux. Is lux a very sensitive scale? A small
tiny increase in lux real life increases the visability a lot? But pcond
's filter is not sensitive enough, and also the limitation of the
monitors contrast and lighting abilities not enough to show any
difference? So many questions!
 
The problem is that using the RGB lighting values suggested, they don't
appear to be able to illuminate the manuscript to a reasonable looking
level, even though in real life a candle could. Wheres my problem?
 
John
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