View Full Version : Linear Lights

08-10-2004, 10:19 PM
When using linear lights (I am doing a cove light in a drywall bulkhead see attached sketch) the ends of the lights seem to produce hot spots. Is this a bug in lightwave? I tried it in LW7.5 as well as LW8 and got the same results. I could use multiple point lights I guess but it would probably run into a hundred or more lights for all the recessed lighting I have. I also don't know how (it's probably easy) to change the lighting parameters for all 100 lights if I go that way. i.e. changing all the intensites or fall-off so they are the same if they need changing without having to change each one individualy.
has anyone experienced this problem and found any soloutions.
The cove lighting actually runs around the room in the actual rendering but my pitiful sketch illustrates the problem I am having.
I had big problems with speckling of linear lights on my last project and now linear lights seem to still be a thorn in my side. Unfortunately I don't have the years of experience some of you have with lightwave since I have been using Imagine and lightscape for the past 10 years. I keep hoping that things like Linear lights will work for me and I will not have to find work arounds for everthing that Lightwave should do. If that is the case I will stick with old programs. I don't feel like putting hundred of lights in my scenes when about 12 should do the job.

Any help would be appreciated
Thanks in advance

Rob k

08-11-2004, 12:30 AM
Well, that's normal. LW interprets linear lights as arrays of point lights, but unfortunately does not take care of spreading the "energy" evenly. A better way would be using area lights which are also just arrays, but in general work a bit better. If that fails entirely, you should try Spotlights with a projection map - this is perhaps the best way to have some control ofer intensity in areas where lights supposedly overlap. Lastly, if you can afford it and only want a still, use radiosity. Simply model luminous tubes and let the math do its magic. You can change parameters for multiple lights in the Spreadsheet or in LW8 in the new Scene Editor/ Spreadsheet.


08-11-2004, 06:24 AM
Alternatively, place the ends of the linear light inside of some geometry. Create boxes at both ends and see if that helps.

08-11-2004, 06:58 AM
Make sure you have Inverse-Squared falloff on the lights, they will behave more correctly that way.

Remember though, the 'falloff circle' around the light (visible when viewed in a non-perspective view) means something different for Inverse-Squared falloff than Linear fall off.

Linear falloff - edge of circle = when light REACHES 0% intensity

Inverse-Squared falloff - edge of circle = when light STARTS to fade away to 0% intensity

Linear lights are also the worst offenders for grain, and they're very slow! They really need an overhaul IMO.

This is why I don't ever use them! :(

08-11-2004, 07:42 AM

Thanks for the comments since I will be using radiosity I think I will try the luminous tubes and see how that works. I never thought about that. If that Works I will never use linear lights again. I will try it out and post results.

Thanks Mattclary and Matt for your suggestions. I learn more evey day with help of fellow lightwavers and only hope to pass on my knowledge when I am more proficient. I also think that the linear lights should be overhauled. I always thought the linear lights were supposed to simulate flourescent tube type lighting.


08-11-2004, 10:44 AM

I modelled up some polylines with width in Autocad (where I do my modelling for Architectural models) A polyline being a contiuous line with a width I have Assigned (100mm in this case)
I seems to work just great. I may make it more 3 dimensional by giving it a thickness because I presume light from luminous objects will radiate in the direction od the polygon normal. Right now i only have a horizontal line in space and if I give it a thickness I should also get light coming of the sides. I have included a quick fprime render (please diregard the garish colours, I have not changed them yet from the base Autocad colours I used)

08-11-2004, 01:20 PM
Man! I almost suggested using a luminous poly, but assumed you weren't using radiosity.

Radiosity kicks *** when used with F-Prime, FYI.