Contemporary-styled, general purpose 600-watt quartz halogen light for photographic and video applications. Features vented and baffled construction for cool operation. Supplied with permanently attached 2-leaf barndoors for optimal light control and glass shield for safe operation. 80° beam angle. Heavy-duty swivel yoke lets you mount this light in any position on any 3/8 in. to 5/8 in. stand or mount. Switch is unit-mounted and the 10 ft. cord is 3-wire grounded. Finish is photographic black, baked-on enamel. Includes 600 watt DYS/DYV lamp.
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Are you sure your umbrellas aren't too close? I have two constant lights that have NO venting, and 600w, and the only part of my umbrellas that get hot is the metal. The fabric doesn't absorb that much heat.
I started with "studio lighting" using a pair of simple Smith & Victor lights. In my experience they are not as useful as the strobes to which I have since moved, but they absolutely were worth using to learn lighting. One advantage of using continuous lighting is that you can see the effects as you move the lights around, playing with lighting positions and ratios. I don't believe mine were as bright as yours, but it sounds like yours are simply on/off as were mine. I grabbed a couple rotary dimmer switches at Home Depot and spliced them into the power cable (something like these Rotary Eco-Dim 600-Watt Dimmer, White-D-603PG-WH at The Home Depot). These dimmer switches made it easy to adjust the total light and, more importantly, the ratio between my lights without having to move the whole light & stand (because not only is moving back not always an option, depending on how much space you have to work in, but moving the light has secondary effects such as spillage to be concerned with). If you do choose to splice in dimmers, make sure you get ones rated high enough. I'd also recommend splicing the dimmer in closer to the plug than to the light - in my case this kept the dimmer on the ground no matter how high I mounted the light, so the dimmer's weight wasn't free hanging, and I could actuate it with my foot.