EET

LETTERS TO EE&T

Potential sites for solar power

The column on myths in a recent issue, ("The good news on solar power," Sept. - Oct.), mentions rooftops and vacant land and abandoned industrial sites as potential sites for placing solar panels. Other areas often overlooked are the miles and miles of land bordering highways and roads. I once calculated that 10% of peak power consumed in Missouri could be sourced from the interstate highway's right-of-ways not used for transportation. With primary and secondary roads being almost 30 times longer, significant amounts of land are available there as well. Some of the advantages of roadside panels would include: nearby electric distribution lines and electricity-using consumers, and savings due to lower right-of-way maintenance costs.
Emmett R. Redd

Clear now?

The article on CNC in the recent issue ("The energy efficient machine tool," Sept. - Oct.) was difficult to follow. I get the energy proposition, but the discussion was unclear. It seemed to be emphasizing the role of feedback, which relates to the company's core product. If that is the central issue, it's only helpful for the motion, which they make clear is not the dominant part of the energy. The spindle axis, which is always over-spec'd for peak power, needs a current-regulation loop to limit the amount of current to the amount needed to meet the actual load.

I had this done for a customer with a polishing application and it worked well. But we weren't looking for energy savings. I did it so they had some way to control the actual polishing behavior. Without that control, the buffer wheel would get buried in the part and rip it off the mounting. Not a pretty sight.

But I think the same principle would hold true. Closed-loop current control implemented against an error signal from the speed sensor on the spindle would be a simple approach and would get the biggest “bang for the buck” in energy saving.

What do you think?
Steve Meyer

The right color temperature

I have some problems with the recent article on color temperature ("The basics of Color Temperature," Sept.-Oct.). Color temperature is a bit of a contentious issue in the lighting business these days. It seems that less-than-reputable vendors are pushing high-color-temperature lamps using "scotopic" lumens rather than "photopic" lumens as a way to reduce illumination levels (and increase energy savings) in buildings. While I applaud energy savings, I don't want to create harsh lighting environments for people to work or study in day-to-day, which will result from following this article's advice. Our company recommends 4,100K lamps as the highest color temperature for general use.

If you would like, I can put you in touch with a researcher at Penn State who has performed studies in this area.

The skeptic in me wants to know the author's qualifications when it comes to lighting. And does he or she have a vested interest in pushing high-color-temperature lighting?
W. Blair Malcom

The author relies: Let me first address your concerns about my background. I earned a B.S. in Electrical Engineering from Auburn University in 1965. I worked for two years for U.S. Air Force Civil Engineering at Kadena Air Base, Okinawa, Japan, and for seven years as staff Electrical Engineer for U.S. Army Facilities Engineer Activity Korea. Both of these tours included illumination engineering. I currently work for the U.S. Navy at the Naval Air Warfare Center Weapons Div. at Point Mugu, Calif.

And I have no vested interest in pushing high-color-temperature lighting. My recent article is not based on efficacy or scotopic vision. It is concerned only with obtaining neutral white light based on the photopic peak at 555 nm.

Your recommendation of 4,100K as the highest color temp for general use may be valid. However, I have not seen any justification for this. (I've already corresponded with the Penn State researcher, but he has not provided me any of his studies.) Let me just say that anyone who wants to use 4,100K lamps should just be aware that they will not be getting neutral white light, but a cream-colored light.
Charles A. Wilson

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