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Joined: Oct 2000
Posts: 2,723
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Broom Pusher and
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Mike (Trumpy):

Quote
The only down side to these fittings that I have experienced, is temperature changes can cause the light output of the tubes to vary slightly, but it is not a big variation.


This is a very valid statement, as when we use Fluorescent Lamps inside of Walk-In Freezers, where Temperatures are -10ºC / 14ºF and down, the light output is reduced by 10% to 20% - depending on the ambient.

The Ballasts are Program Start, and incorporate an additional heat generating circuit, to keep the Ballastry + Lamps somewhat warm, without becoming a large contributor to heat.

On the Walk-In Freezers, I typically will set a "Target" illumination (in Foot-Candles) for 120% the desired average Foot-Candle level.
For example, if the desired level in the Freezer is to be 30 FC, with highly reflective walls, and fixtures mounted in rows at +20 feet A.F.F., I will set my application's target average level at 40 FC.

If the reflectance is less (darker points, like what would result from brown cardboard boxes on shelving), and/or the mounting height is >30 feet, then I adjust the average FC target by as much as 160%
For example, if 30 FC is the desired target average in the Freezer, I set my application's target to 50 FC average.

No Manufacturer has photometrics for the expected reduction in sub zero environments.
They all say their fixtures work in those environments - which they do, just no one has taken the effort to give actual derated levels.

We have been kind of finding out as we go, to come up with the +20% - +60% figures. So far they have been rather accurate when applied to the typical fixtures we specify and install.

Scott


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Dec 2002
Posts: 337
S
Member
Scott,

Dealing with "cleaner light," sometimes a simple term like this helps others understand the more technical term. How many understand the proper term "Color Renditioning Index" or the more cryptic "CRI." This relates to the visual problems that you mention and what I tend to call harsh light because it hurts my eyes after a time.

CRI - is an approximation based on the complete light spectrum of daylight and that is because we have no official definition of full spectrum light (the sun puts off allot of light that we can not see and even window treatments change the color of sunlight). There is also allot of flawed research into this area and the benefits of full spectrum light effects. Suffice it to say that a definition of CRI=100 was given to the standard incandescent bulb and is the maximum possible value.

Typically lighting designs should not be less than a CRI of 70, and I personally like to light offices at a minimum CRI of 80. Once above 90, the lumens per watt output of the available sources drops off and should be reserved for special cases such as museums or locations where color is extremely important.

Now looking at standard light sources and typical CRI's:

Metal halide: 65-70

High Pressure Sodium (HPS): 20-25

Ceramic Metal Halide:80-92

Highend HPS: 60-85

Fluorescent: 70-95 Some as bad as 50.

Compact Fluorescent(T5): Typically greater than 82, but I had the misfortune of finding some that I bet were about 50 for my house good thing they had an average life of maybe 300 hours (what a waste of money).

LED: Varies to much, look at each individually. New technologies have impooved so much that I am not qualified to guess what they are reaching now for some white sources.

Mercury Vapor: 40-50 (some as low as 20)

Thus, with metal halide fixtures at CRI=65-70 versus T5's at 82 plus the perception is allot more pleasing to the end user.

Joined: Jul 2005
Posts: 183
J
Member
Re the metal halide retrofit, has anyone out there had any experience with induction lighting? I have heard figures of 100,000 hour lamp life, and one third the consumption of metal halide systems, and apparently they are well suited for retrofits, but this could just be sales talk.

Joined: Jul 2004
Posts: 625
S
Member
Originally Posted by sabrown

... we have no official definition of full spectrum light...


Actually we do--the black body radiation of a black body of the specified temperature. The sun is pretty close to a black body radiator. Incandescent filaments are good approximations to black body radiators, which is why they have a CRI of 100%.

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