Source 4 Beam Spread Question

No. For a given technology, less power results in less light.
- Compare domestic 60W and 100W bulbs!

Long-life lamps also have a slightly lower output than the normal-life ones at the same wattage.

The datasheets for the Source Four include tables showing the variation in output between the different lamps one might fit.

For example, the 115V, 300 hour average life lamps have the following initial lumens*

• HPL 750/115 (750W) - 21,900lm
• HPL 575/115 (575W) - 16,520lm
• HPL 375/115 (375W) - 10,540lm

* Initial lumens is the output of the raw lamp. Some light is lost as heat inside the fixture.

No. For a given technology, less power results in less light.
- Compare domestic 60W and 100W bulbs!

Long-life lamps also have a slightly lower output than the normal-life ones at the same wattage.

The datasheets for the Source Four include tables showing the variation in output between the different lamps one might fit.

For example, the 115V, 300 hour average life lamps have the following initial lumens*

• HPL 750/115 (750W) - 21,900lm
• HPL 575/115 (575W) - 16,520lm
• HPL 375/115 (375W) - 10,540lm

* Initial lumens is the output of the raw lamp. Some light is lost as heat inside the fixture.

Thanks for the reply Richard. I appreciate your help. I wonder what wattage the knowledge base article was based upon. Additionally, what is an acceptable range of foot candles for proper illumination of the stage for most productions? I realize that some scenes call for dimmer light than others but how many foot candles of light should one shoot for under most circumstances? I'm sure you've figured out by now that I'm in the beginning of the learning process of stage lighting but I'm trying to learn as much as I can. I'm a volunteer at a community theater and their lighting person moved on and I'm the only one who is willing to try and light the shows properly. I really appreciate your help. 

Bill,

The data sheet for each fixture gives some examples of beam spread and brightness at given distances, as well as the multiplying factors for any distance.  The 36deg one is here :  http://www.etcconnect.com/docs/docs_downloads/datashts/7060L1009_Source_Four_36_Spec_Sht_vG.pdf and they are all available from the Downloads tab of the Source Four Product Page.

As to your "acceptable range" question, I was taught that 100fc is the minimum useful level; anything less than that won't be bright enough to make a difference.  Your mileage may vary, of course.

Good luck!

-Matt Pumplin

Matt Pumplin said:

As to your "acceptable range" question, I was taught that 100fc is the minimum useful level; anything less than that won't be bright enough to make a difference.

For TV purposes, one LD who does major awards shows balances his key lights (followspots) to provide 65fc at the talent, after color correction and such. Of course the gain (iris) on cameras can be adjusted up or down.  The human eye is even more forgiving.