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Logarithmic Dimming


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Hi,

I'd love any insight or links to articles explaining the benefits to an LED fixture offering a logarithmic dimming curve and how this can help? I understand generally that light behaves logarithmically (inverse square law etc) and that logarithmic dimming would therefore help adjust lights closer to how our eyes perceive light differences in theory, but I'd love insight into how people use this tool on set in a real-world environment. 

 

Thanks in advance,

Leo

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I'm sure you've already seen this paper from eldoled.

What we perceive isn't always accurate to actual intensity. Sound may work the same way. Guitar volume pots can be linear or logarithmic as well. I had a log one installed when mine was rebuilt because the original pot was quiet until half-way up.

I don't know how the connection to inverse square relates to human perception.

I think the log dimmers are more for human comfort or ease, like the new pot on my guitar. For film gear, while we make or buy dimmers from off the shelf, it would technically be better to have an accurate change than a perceptually pleasant one. I'm sure some exist but we (I at least) end up dialing it in on the monitor with the DIY dimmer boxes anyway.

Hope that helps.

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Human vision is something like logarithmic. That's why we have gamma curves in displays and cameras.

Probably the best example is f-stops, which look roughly like an even series of steps, but actually represent doubling the light every time.

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I realized I totally mispoke previously.

On your question. Halfing of light is logarithmic, and thats what you meant. And to have dimmers that do the same, yes, I think that would be great. I think some exist, but I'm unsure of their technical accuracy.

What I meant was the same, to have accurate halfing of light in a dimmer (even marked) as opposed to something formulated for a consumer's comfort.

Edited by Stephen Sanchez
Phone typos!!!
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Personally I prefer linear. 50% is 1 stop down, 25% is 2 stops down, 12.5% is 3 stops down etc.

Log curves allow for greater dimming resolution at the lower end of a lamps output.

With a linear curve, the difference between 3% and 6% is 1 stop, and the difference between 50% and 100% is also 1 stop.

Say your dimming resolution is 8 bit. For that one stop difference between 3 and 6 percent you only have about 7 steps of intensity in between, but between 50% and 100% you have 128 steps.

The log dimming curve gives you more resolution to play with at the bottom end of your dimmer, and less resolution at the top end, where you really don’t need 0.4% incremental steps between 50% and 100%.

Ultimately if you are running lamps in 16 bit mode, the argument for log control becomes moot because you have 655 or so increments between each percentage point. 

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