Why do some softboxes have flaps?

[MikeWilkinson]

I understand the usefulness of the velcro back near the fixture, but what about velcro flap openings on the sides of certain softboxes? Do they have a purpose?

 

[thekreative]

Heat vent.

 

[slondon]

Heat vent.

Right. Until recently the lamp in most of these boxes has been an inefficient tungsten globe of 500 or 1000W. Most of the energy consumed produces heat, not light, making the interior of the softbox quite warm.

Today there are more and more florescents used in softboxes. Since they produce 3-4 times the light per watt compared to tungsten a lot less heat is produced for a similar output.

 

[filmat11]

Heat vent , true enough. Also to prevent light from spilling out the back of the softbox enclosure. Flaps are necessary for both purposes, and to allow access for several different sizes of speed rings.