[dstructor]

I made a light box, basically a box with some bulbs & a front screen, and painted the interior flat white

But I could only go as low as 1/50, ISO 400 with f8 for 22 CFL bulbs (~3000w Incandescent, 12 in 2 strips & 10 in a box)
(I originally aimed for 1/100, f8 ISO 100 or 200; that's 2-3 f-stops below)

I feel like there's a point of inefficiency (technical, besides the construction & design)
and i think it's in the interior's reflection
Even reflection of light is not much of an issue since the front screen evens out the light eventually

So, should I keep the interior as it is, flat white or glue some alu. foil inside?

[Nass]

alu reflects more than white. But with a softbox it's quite nice to use white poly fabric and shoot light through and onto that for the whitest whites.

[dstructor]

alu reflects more than white. But with a softbox it's quite nice to use white poly fabric and shoot light through and onto that for the whitest whites.

Didn't get that 2nd part, sorry, plz elaborate

[BrianR]

Here's a comparison of foil and matte white (and mylar and black) lining a homemade softbox. Foil and matte came out the same with regards to brightness:

Even Better Softbox Part Two - The Test Results | DIYPhotography.net

I've made a few small softboxes like the one in the link and had similar results, but the white interior did a better job of making the resulting light source uniform.

Your results might be different since your light box isn't the same. Would it be hard to line yours with foil in a non permanent way to try it out? Even a non-perfect job of lining it might give you an idea if it's worth it.

[jatrax]

Based on my experience with reflectors the aluminum will definitely reflect more light than the white. However, in this situation will it be noticeable?

Most of the light is already heading forward so how much of the total is going to be reflected? 30%? and how much more will aluminum reflect than white, maybe 30%? So using those numbers you get a total increase of maybe 10%. Plug in different numbers and you get a different result.

The only real way to test it on your particular box would be to take a light meter reading with the white and then line with foil and take another reading.

I think in this case it will make a difference but probably not as much as you hope.

Another thought: you used flat white, so you might get some increase by repainting with gloss. But again I think the difference will not be dramatic.

[dstructor]

Based on my experience with reflectors the aluminum will definitely reflect more light than the white. However, in this situation will it be noticeable?

Most of the light is already heading forward so how much of the total is going to be reflected? 30%? and how much more will aluminum reflect than white, maybe 30%? So using those numbers you get a total increase of maybe 10%. Plug in different numbers and you get a different result.

The only real way to test it on your particular box would be to take a light meter reading with the white and then line with foil and take another reading.

I think in this case it will make a difference but probably not as much as you hope.

Another thought: you used flat white, so you might get some increase by repainting with gloss. But again I think the difference will not be dramatic.

between flat & glossy, you're right; not so dramatic

I'm not sure about foil vs. white and in the link to the experiment BrianR linked to it's noted that some light escapes through the material; not my case since i'm using 10mm thick MDF boards

With that into account; how many stops more do you think the foil will put out, compared to the white interior?
1/3rd, 2/3?

[jatrax]

Ok, so you got me thinking and I did some research to satisfy my curiosity. And I got quite an education, using google to search for reflectivity of aluminum foil leads you to all sorts of websites with information on various forms of 'indoor gardening'.

Anyway, the numbers do vary considerably depending on source but these seem to be common:
Reflectivity:
Mylar 95%
Aluminum foil Shiny side 88%
Aluminum foil Dull side 80%
White paint 80 - 85% depending on gloss and brand

So based on that, I would think you would see marginal at best improvement going to household foil but that mylar might make a difference.

It is interesting to note that light wave lengths enter into this and the figures noted above are for visible light. When you discuss thermal reflectivity then foil is far superior with white paint being quoted as only 50% reflective but foil being 85% or more. This is not pertinent to photography but if you are trying to build a 'grow spot' inside of a wooden speaker cabinet then thermal reflectivity is apparently of significant interest.

Who would have thought you could grow tomatoes inside a speaker?

[jatrax]

Another thought, is your box square sided or angled? If the sides are square then you will not see any improvement from the sides, though covering the back in foil might help. One of the ways a purchased softbox increases light is by having the sides angled by design to reflect the light to the front. If the sides face each other it will just bounce back & forth losing even more.

Using black MDF is immaterial as far as 'escaping light', it will not escape but it will be absorbed by the black mdf so no practical difference.

A source of mylar cheap enough to try would be one of those aluminum survival blankets sold most everywhere. Our local grocery store has them for $4.99 I think.

[dstructor]

Another thought, is your box square sided or angled? If the sides are square then you will not see any improvement from the sides, though covering the back in foil might help. One of the ways a purchased softbox increases light is by having the sides angled by design to reflect the light to the front. If the sides face each other it will just bounce back & forth losing even more.

Using black MDF is immaterial as far as 'escaping light', it will not escape but it will be absorbed by the black mdf so no practical difference.

A source of mylar cheap enough to try would be one of those aluminum survival blankets sold most everywhere. Our local grocery store has them for $4.99 I think.

Good point; it's not angled so that makes the only point of improvement is lining the back with foil, right?

I don't think i'll find mylar here

[jatrax]

Good point; it's not angled so that makes the only point of improvement is lining the back with foil, right? I don't think i'll find mylar here

For all practical purposes, yes.

Not sure where 'here' is but I would think those mylar survival blankets to be pretty much universal. And if not available locally then the internet has lots of folks eager to sell you something. It was just a thought in case you wanted to try it. Here is the first link that came up in my search: Mylar Foil Blanket | ColonialMedical.com

[dstructor]

For all practical purposes, yes.

Not sure where 'here' is but I would think those mylar survival blankets to be pretty much universal. And if not available locally then the internet has lots of folks eager to sell you something. It was just a thought in case you wanted to try it. Here is the first link that came up in my search: Mylar Foil Blanket | ColonialMedical.com

Here = Egypt

And if i were to choose between ordering Mylar, waiting >1 week, paying customs & shipping and... vs. going to the kitchen & opening a cupboard, then it's a no-brainer

Will try it and let you know what's up; thanks a ton for all the help, everyone

& jatrax: LOOOOOL

'indoor gardening'

Yea, I've been there, know how you feel man

[magkelly]

A silver or gold metallic reflector or umbrella will generally reflect more light than plain white but it can also cause unwanted warmth or uneven skin tones where you don't want them. I like to use both because sometimes that is what I want a warmer skin tone but using a metallic reflector can be problematic sometimes when it comes to photographing people with very light or very dark skin. Metallic reflectors can cast reflective tones I actually don't want as well as ones I might. I'd rather use more white, than gold or silver most of the time because it's more neutral even though it means using more of it. I've started using my own home done version of a V-flat a lot and white reflectors in the front et all because I think it's a bit nicer on the skin.

I have studio lights and flashes and I use them sometimes but I really prefer a more natural looking light and I think the V-flats and a window or other source of light with diffusion gives me that. V-flats, a window, some sheers doubled up, maybe a white reflector, that's near perfect portrait lighting for me unless I want to go dark and moody. I actually like the foil reflectors used more outside where it's hard to set up a V-flat and where you'd actually expect more of a sun kissed skin tone. Inside I think they can make some skin look a bit sallow and who wants that?

For general use in other words I prefer white but there are certain situations where gold and silver can work.

[dstructor]

By the way: my next project will be making a spiderlite-like fixture that would hopefully support about 8 CFL bulbs and could be fitted with a regular commercial soft-box

[Ponosby Britt]

These are sold as emergency blankets for a few dollars. You'll get a lot of Mylar.

Amazon.com: Emergency Blanket: Sports & Outdoors

[jatrax]

By the way: my next project will be making a spiderlite-like fixture that would hopefully support about 8 CFL bulbs and could be fitted with a regular commercial soft-box

Electrical boxes plus adjustable light fixtures like used for outdoor floodlights. Sounds like fun!

But unless you can scrounge the materials I think it would be cheaper to buy it ready made with the softbox. Like this: Six Head Light Socket

I know I could not buy the parts locally for that.