Simulating LED lighting...

Hi,

I've used sketchup to model my bathroom renovations. I then decided to check out iRender-ntx to know how many and what kind of LED lights to stick in it.

This has proven to be one difficult task. The help talks about conversion between watts and lumens, and it also states that I should be able to specify brightness in lumens, but that doesn't appear in the version I've been playing with (KI27, downloading KI30 now).

So moving on, I decided to just brute-force it, having a fair idea of how the lighting aught to work. So I stuch 3 spot lights on the plinth of my vanity each at 40 watts (all other setting their defaults). This was far to bright. So I modified this down to 20 watts, then 10, then 5, then 1watt. So my model was down to 3 x 1watt spot lights - what in reality woudl be just a dim night light at best. But all of these way over render the real light that would be in the room. One could say the spot light is more like a flood light :)

And yes I have Ambient light set to None but I cannot turn off the Artificial light checkbox because it causes Sketchup to crash.

So my question is - how can I simulate LED lighting (or more generally low lighting) and only the lighting coming from my light sources - no other artificial lights? Me thinks it isn't possible, at least not with this software.

I could dim the brightness on the rendering screen - but that is cheating... and defeats my purpose. Recall that my end-game goal is to know what sort of lights to purchase. If I hand modify the brightness so it is lite like I want it - well that doesn't help me at all in determining what I should go out and buy. That just aids in making a pretty picture.

cheers,

-randall

ps- attached is the 3x1watt image

Attachments:

Bathroom8 - spot floor light tinkering Scene1 1watt floor lights ONLY.jpg, 174 KB

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Permalink Reply by Roy Hirshkowitz on October 9, 2011 at 1:50pm

He could save the image out as an HDR and bring it into another application which offers a choice of tone mapping operators, particular ones which take into account human visual perception at low light levels.

If the lighting in the room is at the photopic level (> 1 cd/m^2), then it's likely that the only apps. he could find to display any differences would be "research" ones. The differences would be subtle here-- for example whether you could read text in that light level, etc..

If the lighting is dim, then there probably are some out there which take into account human visual perception at low light levels. I don't know what's available though.

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Permalink Reply by Mike Halls on October 9, 2011 at 3:24pm

I think this 'client' is missing the point !.

This is not a lighting design programme, it is a Visualisation programme, and he does not seem to think it worth his while to explore the many subtle features of Irender NXT before posting a, frankly, aggresive post.

When I decide on lighting for one of my interiors I have a pretty good idea of the effect I want to achieve and I have enough knowledge to know what fittings to specify to achieve the effect I desire, irenderNXT gives me the ability to visualise the end result. OK it takes a bit of work but me, and many other users, get great and realistic interiors using artificial light. Suggest this 'client' puts all his circuits on dimmer switches as he does not seem to know what effect his light fiting descisions will have on his interiors.

This is agreat peice of software, OK a bit of a learning curve on some of the more subtle features regarding lighting - BUT WORTH EVERY MINUTE !

Regards

Mike

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Permalink Reply by Roy Hirshkowitz on October 9, 2011 at 3:58pm

It's actually not a terrible comment. He is pointing out a legitimate "shortcoming" in the tone mapping operator used by nXt, albeit one we know about and have intentionally left in. While nXt is useful for many, many lighting simulations, it is not providing a useful answer to the question Randall is asking.

I'm glad you're enjoying the software and look forward to seeing your work.

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Permalink Reply by Render Plus on October 9, 2011 at 4:46pm

Mike has uploaded some nice image to the gallery, such as this one: Control Room

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Permalink Reply by Alain Bonnefoy on October 12, 2011 at 12:38am

Well, "Watt" is a unfortunately something which widely cause problems when choosing light technology. Manufacturer took this unit in the past, which doesn't mean anything, even if a unit was existing to measure illumination.

As "Watt" is also an unit used for energy (used to define candela) it's possible that "Watt" was not the Electrical "Watt" at the begining, but the Energy one. Maybe it's the reason of the mistake.

Ok, using lumen (a bit subjective), lux (widely used) or better, candela, was maybe considered not so obvious. But candela is well defined unit in the IS. IS, you know? the International System where the very convenient "meter" is defined. LOL. Sorry.

When fluorescent technology apppeared, it was time to supposed that "Watt" would cause problem. Anyway no decision was taken to eliminate "Watt". It was not a very big problem because fluorescent technology was a good lightning alternative but it became a nightmare for us when LED came on the market (I want to talk about power led), and a chance for manufacturers who successfully sold some products manifestly not able to enlight anything (Now it's a bit better but widely depend on manufacturers). At that time, they introduced Lumen (why not Candela???) but nobody have any idea on how many lumens an incandescent light gives. So no comparison possible. They bought LED which terminated in the trash.

Another problem is that incandescent or fuorescent lights are multidirective. A LED not.

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Permalink Reply by Roy Hirshkowitz on October 12, 2011 at 9:39am

Lumens and Candelas are both SI units. Candela has directionality and is defined as 1 lumen / 1 steradian. Lumens measure the total output of a source, candelas measure the intensity in a particular direction.

Most LEDs used for lighting are now specified in lumens and beam angles. Some, particularly indicator LEDs, are still specified using maximum or average candelas (millicandelas) and beam angle. The beam angle, BTW, is defined as the angle at which the luminous intensity is reduced to 1/2 the maximum, just as it is in our spotlight distribution. If you know the average candela and the beam angle you can convert to lumens using this site (it won't work for max candelas.)

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Individual LEDs are actually well modeled by nXt's spot light distribution. If you need to be more accurate use a spot light with the specified beam angle. (This degree of accuracy is rarely required.) Again, to convert from Watts to Lumens simply multiply by 17.