I'm assuming these are to go into
R40 strips, such as these?
http://mail.altmanltg.com/publicsynergy/docs/BLItemDossier.asp?Item=520-6&PLID=&Country=US
The spread or
stipple variety help to alleviate "
scalloping" aka "color fringing" clearly shown in this picture:
http://www.controlbooth.com/forums/lighting/9831-cyc-light-recommendations.html#post111001
As Icewolf said, rondels come in three flavors:
clear (smooth on both sides),
stipple (texture similar to R100 on the inside), and spread ([I believe it's usually 40°] heavy parallel lines meant to spread the light along one axis, an
effect similar to R104).
If your striplights are in fact
R40 strips, they probably take a two part metal "combination" frame. Putting the two pieces together one way leaves a 1/4" gap for the
rondel. Reversing the inner piece allows for
gel to be sandwiched between the two pieces. If yours are like this, I would not be buying rondels, which are expensive, heavy, breakable, and come in limited colors. I'd use plastic colr media (
gel), in either R120,121,122 or R124,125,126; and still maintain the possibility to put in any of the approx. 800 colors available accross the four major manufacturers.
The
clear or plain rondels will pass the most light The spread will pass the least. Actually the light loss through the glass is insignificant--the loss of
intensity comes as to how the light is distributed. Before ordering an entire set, see if your vendor can supply you with one of each type with which to experiment. As you're looking at approx. $25/each for all types, this is a significant expenditure.
This
page shows
Altman 5 5/5" rondels and the combo color frame for
R40 strips.
edit:
...I have six 8" strips 4
circuit. ...
Okay, ignore what I said about
R40 strips. Do you have PAR56, PAR64, or older style strips using 200W/300W A-lamps?
These?
http://www.controlbooth.com/forums/glossary/11139-blinder.html
All the more reason to buy
gel instead of glass if at all possible. Rondels in 8" variety are freakin' expensive! If the fixtures cannot take
gel, you may want to look at a product from
http://www.fxlight.com/ez-ht.html.