continuous lighting - to multi bulb or bump up the power?

Is there an equation or chart for brightness and multiple bulbs of the same or differing brightness. If I had say 1 bulb with 1700 lumens on an umbrella what effect would adding an additional bulb of the same make have?

I've been going from CFLs to LEDs and now have some 150W and 200W incandescents on order. So far LEDs are my bulb of choice just not quite bright enough in single bulb setups.

Maybe there's someone knowing more about it but if you want to calculate the required brightness for an area, you have to use lux to find out how much lumen you need.

1lx = 1 lm/m2

The problem had me puzzled a while ago when shooting smoke. I was first using a 400 lm LED and then got one of those magnesium work lights that had more than 8k lm. Strangely, it didn't seem to do more in regards to lighting the smoke. The reason was simple: because I had to move the lamp further from the subject, now those 8k are divided by the increase in square meters resulting in roughly the same output on my subject. To up the required subject output, I'd have to up the total lumen a whole lot more.

ideacipher said:

Is there an equation or chart for brightness and multiple bulbs of the same or differing brightness. If I had say 1 bulb with 1700 lumens on an umbrella what effect would adding an additional bulb of the same make have?

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Two equal bulbs are twice as bright as one, which is one stop.
Four bulbs are 4x, which is 2 stops.
Doubling the number of bulbs is one stop (eight is 3 stops more than one).

I've been going from CFLs to LEDs and now have some 150W and 200W incandescents on order. So far LEDs are my bulb of choice just not quite bright enough in single bulb setups.

Click to expand...

That is the problem with continuous light (dim). It never does the camera any good unless the shutter is actually open.

So... 500 watts and a 1/100 second shutter is 500 x 1/100 = 5 watt seconds of energy converted to light (all that is usable).

Speedlights are 60 to 75 watt seconds. Vastly more efficient. And they are fast, can deliver it all into any shutter speed (up to 1/200 second sync speed).


Incandescents have much less efficiency than CFL or LED. Hotter too, since the power mostly goes into heat. This is the conversion when 26 watts CFL is called 100 watts, because it is equivalent light to a 100 watt incandescent -but only draws 26 watts power (and heat).