user6398: I'm shooting in a small apartment and I have had a lot of trouble setting up a back light because the subject is directly against a wall.
I am looking at kits like this one, but I was surprised that what I assume is intended to be a back light is a softbox!
Is it normal to use a softbox for a back light? It seems like it would diffuse the light too much and it wouldn't work as a backlight. Additionally, wouldn't it leak light onto the wall behind the subject? (Maybe those concerns can be addressed with the use of grids?)
I thought for a back light you needed to get a spotlight to shine a narrow beam. Would a softbox like the one above work if hung directly above the subject who has their back one or two feet from the wall? Would it be better to get a reflector light like this one?
If a reflector light is better, why do most of the kits include light boxes on the booms instead of reflector lights? 

user2836: It may be a backlight, or it may be an overhead light for use in getting the noir look.  Either way, use of a softbox is fine.  It would actually have a narrowing impact on the category of the light rather than a widening influence.  The light itself in that kit radiates light in all directions, the inside edges of the soft box bounce that light forward, it then hits the diffuser and gets transmitted through the material, resulting in a kind of virtual light source that has a much larger surface area with light that is more directed than the original light was (but less so than if the diffuser panel had been left off or than if a grid was used.
Depending on how you use it, it shouldn't leak light on to the wall behind the subject as it is going to primarily throw light forward in a wide arc, but it will block light from going behind it.
You could use a grid to focus the light in a particular direction, but then using the soft box wouldn't make sense.  The entire point of a soft box is to diffuse the light so that each point in the scene is hit from multiple angles and makes shadows softer.  A grid is designed to do the opposite and ensure that each point in a scene is hit by the minimum amount of light sources.
As far as if it would work directly overhead, it could work directly overhead for some shots, though either slightly in front or, more ideally in most cases, slightly behind is preferable.  This is simply because a lot of your light is going to come from your key and fill for the front and directly down light will interact with the key and fill lights in a way that often isn't desired (making the tops of facial features brighter and recessed features like eyes darker.)
A backlight doesn't have to be focused, what is important is that the shadows that fall on the backs of people get light and that you have light reflecting off of slightly reflective surfaces like hair and such to give things more pop.  A highly direct light will make parts of this effect stronger, but you get different qualities with a softer light.  Neither is wrong, just depends on what you are looking for.
Reflector lights aren't better, they are just different.  A reflector is a lot like a softbox without the front panel and some nicer kits actually have a softbox where the diffusion panel can be removed.  This way you can get the best of both worlds in a single kit.

user6179: Is it normal to use a softbox for a back light? 
It can be sometimes. With two softbox lights, one can very nicely, evenly light a background show here. Note in the video that the subject is much farther than 2ft from the background. 
Wouldn't it leak light onto the wall behind the subject?
Yes, it would, but not because it's a softbox. Softboxes only cause less harsher shadows. The reason it would spill light all over your scene is because the light inside of the software box is not directional at all, but rather an open-face bulb. 
Maybe those concerns can be addressed with the use of grids?
The purpose of a grid is to shape light and contain it. So, with that in mid, a fabric grid would help reduce spill onto your subject and wherever else you don't want it.
Would a softbox like the one above work if hung directly above the subject who has their back one or two feet from the wall?
It really depends on what kind of look you're going for. What color are your walls? If they're white, the light will likely reflect off of the wall and bounce back onto your subject creating a rim light around them and illuminating the back wall. It won't illuminate it evenly (a single softbox light), however, and will likely have a gradient from light to dark, top to bottom. 
If a reflector light is better, why do most of the kits include light boxes on the booms instead of reflector lights?
Nothing is better, per say. Light is highly dependent upon the situation. You as the videographer need to figure out which lights are best for your situation. 
I would like to take a moment to say that when it comes to light, the whole motto "buy once, cry once" i.e. get good quality lights, rings true. The kit you linked, while I've never had experience with, will likely not last you very long and be a poor investment. You should consider purchasing used, well known name brands, or rent until you can afford real lights (if budget is a concern). Again, I don't know what kind of production you're running, but this is the advice that I've come across time and time again. A good starter set for interview style set ups, is this guy. Additionally, tungsten lights are cheap and render skin tones very nicely. Some brands to find used Tungsten lights are Arri and Mole-Richardson. Try to stay away from off-brand LED lights. 
This is only scratching the surface. 

6398: <p>I'm shooting in a small apartment and I have had a lot of trouble setting up a back light because the subject is directly against a wall.</p>

<p>I am looking at kits like <a href="http://www.cowboystudio.com/product_p/vl-9004s-b6.htm" rel="nofollow">this one</a>, but I was surprised that what I assume is intended to be a back light is a softbox!</p>

<p>Is it normal to use a softbox for a back light? It seems like it would diffuse the light too much and it wouldn't work as a backlight. Additionally, wouldn't it leak light onto the wall behind the subject? (Maybe those concerns can be addressed with the use of <a href="http://www.cowboyestudio.com/product_p/vl-9004s-b6-grid.htm" rel="nofollow">grids</a>?)</p>

<p>I thought for a back light you needed to get a spotlight to shine a narrow beam. Would a softbox like the one above work if hung directly above the subject who has their back one or two feet from the wall? Would it be better to get a reflector light like <a href="http://www.cowboystudio.com/product_p/803-sboom-26w-ps04.htm" rel="nofollow">this one</a>?</p>

<p>If a <code>reflector</code> light is better, why do most of the kits include light boxes on the booms instead of reflector lights? </p>
 2836: <p>It may be a backlight, or it may be an overhead light for use in getting the noir look.  Either way, use of a softbox is fine.  It would actually have a narrowing impact on the category of the light rather than a widening influence.  The light itself in that kit radiates light in all directions, the inside edges of the soft box bounce that light forward, it then hits the diffuser and gets transmitted through the material, resulting in a kind of virtual light source that has a much larger surface area with light that is more directed than the original light was (but less so than if the diffuser panel had been left off or than if a grid was used.</p>

<p>Depending on how you use it, it shouldn't leak light on to the wall behind the subject as it is going to primarily throw light forward in a wide arc, but it will block light from going behind it.</p>

<p>You could use a grid to focus the light in a particular direction, but then using the soft box wouldn't make sense.  The entire point of a soft box is to diffuse the light so that each point in the scene is hit from multiple angles and makes shadows softer.  A grid is designed to do the opposite and ensure that each point in a scene is hit by the minimum amount of light sources.</p>

<p>As far as if it would work directly overhead, it could work directly overhead for some shots, though either slightly in front or, more ideally in most cases, slightly behind is preferable.  This is simply because a lot of your light is going to come from your key and fill for the front and directly down light will interact with the key and fill lights in a way that often isn't desired (making the tops of facial features brighter and recessed features like eyes darker.)</p>

<p>A backlight doesn't have to be focused, what is important is that the shadows that fall on the backs of people get light and that you have light reflecting off of slightly reflective surfaces like hair and such to give things more pop.  A highly direct light will make parts of this effect stronger, but you get different qualities with a softer light.  Neither is wrong, just depends on what you are looking for.</p>

<p>Reflector lights aren't better, they are just different.  A reflector is a lot like a softbox without the front panel and some nicer kits actually have a softbox where the diffusion panel can be removed.  This way you can get the best of both worlds in a single kit.</p>
 6179: <p><strong>Is it normal to use a softbox for a back light?</strong> </p>

<p>It can be sometimes. With two softbox lights, one can very nicely, evenly light a background show <a href="https://www.youtube.com/watch?v=HeRQFFIgp24&amp;list=UU8Pksdbj37CdE00kmE7Z1dw" rel="nofollow">here</a>. Note in the video that the subject is much farther than 2ft from the background. </p>

<p><strong>Wouldn't it leak light onto the wall behind the subject?</strong></p>

<p>Yes, it would, but not because it's a softbox. Softboxes only cause less harsher shadows. The reason it would spill light all over your scene is because the light inside of the software box is not directional at all, but rather an open-face bulb. </p>

<p><strong>Maybe those concerns can be addressed with the use of grids?</strong></p>

<p>The purpose of a grid is to shape light and contain it. So, with that in mid, a fabric grid would help reduce spill onto your subject and wherever else you don't want it.</p>

<p><strong>Would a softbox like the one above work if hung directly above the subject who has their back one or two feet from the wall?</strong></p>

<p>It really depends on what kind of look you're going for. What color are your walls? If they're white, the light will likely reflect off of the wall and bounce back onto your subject creating a rim light around them and illuminating the back wall. It won't illuminate it evenly (a single softbox light), however, and will likely have a gradient from light to dark, top to bottom. </p>

<p><strong>If a reflector light is better, why do most of the kits include light boxes on the booms instead of reflector lights?</strong></p>

<p>Nothing is better, per say. Light is highly dependent upon the situation. You as the videographer need to figure out which lights are best for your situation. </p>

<p>I would like to take a moment to say that when it comes to light, the whole motto "buy once, cry once" i.e. get good quality lights, rings true. The kit you linked, while I've never had experience with, will likely not last you very long and be a poor investment. You should consider purchasing used, well known name brands, or rent until you can afford real lights (if budget is a concern). Again, I don't know what kind of production you're running, but this is the advice that I've come across time and time again. A good starter set for interview style set ups, is this <a href="http://www.bhphotovideo.com/c/product/285886-REG/Lowel_LCP_944LB_Rifa_eX_44_Pro.html" rel="nofollow">guy</a>. Additionally, tungsten lights are cheap and render skin tones very nicely. Some brands to find used Tungsten lights are Arri and Mole-Richardson. Try to stay away from off-brand LED lights. </p>

<p>This is only scratching the surface. </p>
