Thursday 8 November 2018

lighting - How do I compare a continuous light panel's brightness vs. flash through a softbox?


I've been following recent developments in light-emitting capacitor technology with interest. This new technology produces a complete-spectrum light (like sunlight or incandescents), instead of the spiky spectrum of even the best LEDs and fluorescent lights. And it comes in durable, flexible panels up to 3' x 6' (1m x 2m), in pretty much any color temperature. And, looks like products will be coming to market at the end of the year, for not-unreasonable prices. Looks like they're targeting advertising displays and commercial lighting initially, but given the properties it seems like this is even better for photography than the LED-array panels which are catching on these days.


The only catch is that the current models aren't very bright. They're planning to get more so, but right now engineering samples have a luminance of 200 cd/m², with 600-1000 cd/m² samples planned for the end of the year. That's not particularly bright in absolute terms, but here the whole surface is the light, so it's different from an LED or a single bulb. It seems like the most apt comparison would be a softbox (which, theoretically, such panels might replace). But I'm getting kind of twisted up trying to figure out the equivalent with formulas. Rather than trying to compare candelas and lumens and watts, how can I put this in straightforward camera exposure terms for a given situation?


Let's say I had a 1000cd/m² LEC panel which was half a square meter (roughly like a 28"×28" "traditional" hotshoe-flash softbox). With my subject a meter from the panel, what aperture and shutter speed would give me a correct exposure at ISO 100?


And, how would that compare with a, say, GN 36 flash through that 28"×28" softbox? What about incandescent light of 100W, again, with whatever is needed to diffuse nicely so the light source is effectively that area?




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