Reflectivity of white paint vs. mylar

>From: Petemohan at aol_com
>Date: Fri, 21 Feb 1997 19:29:58 -0500 (EST)
>Subject: Re: Aquatic Plants Digest V2 #530
>In a message dated 97-02-19 21:51:45 EST, you write:
><< From: "Justin P. Healy" <jphealy at sysconn_com>
> Date: Wed, 19 Feb 1997 08:11:52 -0500
> Subject: Reflectivity of white paint vs. mylar
> A recent post said that white paint is nearly as reflective as mylar. I
> sell a variety of radiant barrier materials for a living. The plain fact is
> that the absolute BEST reflector is a mirror finish. Mylar will be
> significantly better as a reflector than white paint.
> Justin in Savannah where Spring is springing.
>  >>
>For the sake of clarity let me point out I was comparing mirror GLASS with
>white paint.  Silvered glass reflects only 88 - 93 of incident light
>according to my trusty, if outdated, copy of the CRC Handbook.  Certain white
>paints reflect 85 - 98 percent of incident light.   Do you have reflection
>coifficients for your mylars? 
>Pete Mohan  

You don't want to compare silver glass (glass mirrors) to white paint for
use in an aquarium. People typically don't use glass mirrors in light
(You lose about 10% of the light in a glass mirror due to light going
through glass bouncing off the silver and then back out through the glass.)

You want to use the polished aluminum or coated silver reflectance numbers
for comparisons. There you can see reflectance values in the 85 - 95 percent

It seems like we are having yet another white paint vs. silver/aluminum 
flame war!!!!!

As an experiment I used an off the shelf KMART Liteway brand shop light.
These shop lights cost about $11 US for a dual bulb 40 Watt T12 fixture.
I used the same two Philips F40T50U (Daylight) bulbs in this experiment.

I measured the light levels at various points around the light 
using a Sub-Lux Light meter.  I measured several points around the bulbs,
since one measurement directly underneath the bulbs may not tell the 
whole story.

One of my comparisons was between the standard white reflector that
comes with the shop light and regular aluminum foil.  For the aluminum foil
case, I just lined the inside of the reflector.  I did not bother to
get all the wrinkles out.


What I found is the the aluminum foil covered light fixture had a consistent
10% IMPROVEMENT in measured light levels compared to the off the KMART shelf
white reflector at all the various points measured!!!!


I also looked at other variables using this set up.  I looked at several
types of T12 bulbs (Cool White, Vitalite, Agro Lux, etc).  I also looked at 
a half dozen different T8 electronic ballasts and also compare them to
a 2x55 Watt Compact fluorescent lamp setup.

If anyone is interested, I'll try and "publish" these results somehow on
either on the NET or maybe the (if they let me) AGA magazine.

Ron Wozniak  Allentown PA, USA
rjwozniak at lucent_com