Recreating street lights

[jim_johnston]

Hi all,

I'm making a scene that will involve soudium-vapor lamps (the typical street lights you see here in the UK). I've gathered some information but was wondering how I would transfer this information into Houdini?I assume you just punch in the colour temperature but I thought I'd come fishing for tips to get a realistic result.

I was especially interested in hinting at the 'stroboscopic' effect you see when in an environment only being lit by these lights (due i assume to the slow wavelength).

Cheers,

Jim

 

[Skybar]

Yes I suppose just punching in the color temperature gives you the right color. As for the "stroboscopic" effect you speak of I don't really know, but that doesn't have anything at all to do with the wavelength of the light - but rather the Hz (hertz) the electricity is working at. I don't know what you have in the UK but here in Sweden we have 50Hz. Edit: or if you mean when the light turns on? That's probably caused by the lamp warming up - there might be some measurements for that out there, if not just opting for some arbitrary flickering that looks artistically alright.

Edited May 24, 2015 by Skybar

[Guest tar]

(due i assume to the slow wavelength).

 

 

 

Most likely the 50Hz power supply than the light frequency of 508 trillion Hz.

lambda * nu = light speed.
5.9E-7 * a = 3.08E+8
 3.0E+8  / 5.9E-7   =  a  = 5.08E+14 /sec

The 50Hz power supply is most likely being noticed on the more sensitive part of the eye, outside the fovea . Lamps when filmed at higher speed should show this. You would want to recreate it by slighting dimming and back to full power in 1/50sec

 

The light pattern on the road might be able to use an ies profiles, some found in $HFS/houdini/ies/, or a Projection Map you could create.

The glow you would do in post.

[jim_johnston]

Hahaha yes, i meant the Hz, but that could be a good project though (to visualize the colours in a scene much slower, so you could see the separate frequencies oscillating). Thanks for the interesting posts Skybar and Marty.

Also cheers for the heads up about IES profiles, that would had been my next question!

[Skybar]

I found this:

 

A different, much higher frequency, normal electric-arc "flicker" might be what's in question: Once an arc lamp reaches proper operating temperature, the arc will go out then re-strike normally with each zero-crossing of the ballasted, alternating-current power supplying the lamp.  This flicker rate will be twice the power frequency (once for each half-cycle).   Unlike fluorescent lamps, there is no phosphor's persistence, nor a possible electronic high-frequency inverting ballast to moderate a sodium vapor lamp's line-frequency-based flicker.

 

And I think that makes sense. So it would be a 100Hz flicker on a 50Hz electrical grid