Best Light Blocking Color

Thomas E. Johnson · Post by **Thomas E. Johnson** » Sun Dec 17, 2006 11:59 pm

I've been told that silver paint is a better light blocking color than black. Is this true? What is the best color if neither silver or black?

rpauly · Post by **rpauly** » Mon Dec 18, 2006 1:02 am

I use both. A coat of flat black to block, then silver to help reflect the light. I've heard white is better for distributing the reflected light - gonna try that my next lighted build...

Zen-Builder · Post by **Zen-Builder** » Mon Dec 18, 2006 1:09 am

I usually got with a coat of black and then white.

That is for projects that require a LOT of coverage, otherwise I use a double sided silver sticky tape.

FYI, the Z Gundam PG Kit also uses the white side of a silver backed tape to defuse the light, confused the hell out of me initially.

Kylwell · Post by **Kylwell** » Mon Dec 18, 2006 10:31 am

Black then white.

Why white instead of silver? Less hot spots and seemingly more opaque.

DX-SFX · Post by **DX-SFX** » Mon Dec 18, 2006 3:13 pm

The reason silver blocks the light so well is because it has totally opaque particles of metal in it. It makes a very efficient light baffle. It also has the benefit of bouncing light around the interior of a model making the lighting more even and brighter. White is actually one of the least opaque as anyone who 's tried to spray it over a bright colour will testify. It is good for keeping light levels high internally though. Black baffles quite well (depending on brand) but kills brightness levels.

Kylwell · Post by **Kylwell** » Mon Dec 18, 2006 3:24 pm

Acutally most silver paint has a lower albedo than white make the light less bright. People tend to think silver paint is the same a mirror polished metal or chrome at it is not.

ignatz · Post by **ignatz** » Mon Dec 18, 2006 3:37 pm

Reflectivity aside, silver paint seems to be more opaque than any other paint. I've done some test a couple of years back and almost all other paint colors have some level of light bleed. The metallics were either opaque or nearly opaque--at least to the point where I couldn't discern any light bleed.

DX-SFX · Post by **DX-SFX** » Mon Dec 18, 2006 5:19 pm

Silver has a slightly brighter reflectancy than it's grey tone equivalent in a diffused situation. White is definitely the best in that respect but silver and it's metallic relatives, wins hands down in the paint opacity stakes.

In reflective terms, photographic reflectors tend to be white or silver or gold if you want to add warmth to portraits.

Kylwell · Post by **Kylwell** » Mon Dec 18, 2006 5:28 pm

but they are not painted with silver paint (from any of the popular hobby paint suppliers).

The thing that makes silver paint such an efective light block (micro small plates of metal or metal substitute) act as a light trap, which also means that the paint will absorb light as well as reflect it.

Even in photography you use a silver or gold bounce board for diffuse light, white for a brighter bounce light.

DX-SFX · Post by **DX-SFX** » Mon Dec 18, 2006 8:28 pm

If you go back and read what I posted, that's exactly what I said.

The thing that makes silver paint such an effective light block (micro small plates of metal or metal substitute) act as a light trap, which also means that the paint will absorb light as well as reflect it.

Yes, see my first post.

Let's not muddle the two. First, opacity: The metal particles are an opaque barrier in the same way that a brick wall won't allow light to pass through. This refers to the context that the original poster asked about which was, presumably, about painting something to make it light tight so that internal illumination doesn't show through. Any paint with opaque overlapping material in the carrier film will stop light penetrating. Silver is very good at it. It doesn't matter if subsequent coats are opaque or not because the metal particles will do the job.

Reflectance: In the context of reflection, silver paint or silver fabric will reflect a proportion of the light falling on it.

Even in photography you use a silver or gold bounce board for diffuse light, white for a brighter bounce light.

Yes the white is better in that context if you want a diffused light source but reflectance and diffusion is based on the smoothness of the surface. The smoother the surface, the more directional the reflection will be. That is also true for silver. A mirror is a near perfect directional reflector. Silver paint or fabric absorbs some of the light, i.e reflects less of it and scatters what it does reflect. White appears brighter that silver paint because it reflects more of light that falls on it. Silver, being darker in tonal value, as posted, does not reflect the same proportion of the light falling on it, in the same way that black reflects almost none of the light that falls on it.

A. Point a light at a mirror and take a light reading with a meter in the reflected beam of light and you will get a higher reading than doing it with a white board or silver at the same distance. You will get a light reading virtually the same as if you stood the same optical distance from the light without a mirror in the path.

B. Point a light at a painted silver board and take a light reading at the same point and the reading will be vastly reduced compared with the mirror. This is due to some of the light being absorbed and some of it being scattered.

C. Point a light at a white board and take a meter reading and you will get a brighter reading than the silver board because almost of the light that makes up white light is getting reflected although it is still being scattered rather than all of it going in the same direction.

D Point a light at a mirror that you've lightly sprayed with matt varnish (theoretically a clear film that roughens the surface so that the light is scattered in all directions). A light spraying will scatter some of the reflected light but a lot will reflect as per the clean mirror. If you keep adding matt spray, the mirror effectively turnes into silver paint in that the same quantity of light gets reflected and the same degree of scattering occurs as happens with silver paint.

If you could gather all the light coming off the mirror and the piece of white board, the total would be roughly equal because neither surface has absorbed any of the light. The difference is the mirror sent it all back in one direction and the white board scattered it in all directions. The mirror reflects all the light hitting it effectively 100%. The white board does the same but not directionally (actually the total light reflectance of white is still lower).

The silver paint appears darker because although it scatters the light in exactly the same way the white board does, it absorbs some of the spectrum so less total light is reflected regardless of which direction it is reflected.

The gold board absorbs more of the cool colours of the spectrum and reflects more of the warm hues which is why gold looks like gold. Like the silver, it reflects only a part of the spectrum and what it does reflect it scatters in the same way. Photograph both the silver and the gold on black and white film, which doesn't record hue but does record light intensity and you'll see that silver and gold look the same because the reflectance is similar. The white board also scatters light in exactly the same way (I'm assuming the board is matt so as not to complicate the example) but it reflects a larger proportion of the light spetrum falling on it than the silver or gold so it appears brighter on black and white film.

If you want a paint that is opaque to light, that stops light penetrating through, silver is generally the best. If you want a paint that reflects light in a diffuse fashion the most intensely, white is the best. If you want something that reflects light directionally with the most inensity, then you want chrome or a mirror.

Where exactly are we disagreeing?

Rio · Post by **Rio** » Mon Jan 08, 2007 3:17 pm

Thanks guys for all the tips/help. While musing about reflectance/blocking, it occurred to me that if I lay pieces of Reynolds aluminum paper, attaching them with that spray adhesive available at stores, it might solve both light transmission/blocking problems.
I gotta try that!

RiÃ¶<*>
Semper Sci Fi!

dekesdragon · Post by **dekesdragon** » Thu Jan 11, 2007 7:09 pm

in my experience
black for light blocking.
I keep jars of old black paint for such purposes.
I will paint any interior of a slightly opaque model with black before assembly.
Now if your are looking at lighting and light blocking, slightly different story
I would go with black
and then do what Rio said, foil (scaping where needed to apply glue)
or if you are rich, bare metal foil
depending on how much is needed.
FSM has had lighting a model articles in the past that give a goog nuts and
bolts basics
see also the kalmbach sci-fi ship book for ideas