Multiple weak light bulbs vs one strong light bulb

Question

I currently have a small room with a single CFL bulb at the center of its ceiling. The bulb lights up the whole room well enough. I encounter the problem though that when standing in front of the mirror mounted on the wall of the room, I block the light, keeping it from reflecting light onto myself.

Because of this, I plan on installing multiple light bulbs in the room so that theoretically, there's at least one or so light sources directly lighting any point of the room where ever I stand. Of course, to conserve energy and to keep the room from getting too bright and hot, I intend on installing weaker light bulbs.

I also plan on buying LED bulbs so my solution above should solve the "non-omni-directional"nature of the bulbs.

Do you see any problem that might arise with my solution? The problems I see are the cost of the LED bulbs and the effort to install more sockets in the room for the bulbs. These are trivial in my case though since I'm willing to spend the time and money to install them.

PS: My current CFL bulb is rated with 820 lumens. Would buying multiple bulbs whose lumens ratings sum up to 820 light up the room just as well? I plan on installing them on the edges or corners of the ceiling, each pointing to the center, so I'm guessing that the lumens WILL add up based on what I've read after googling. Correct me if I'm wrong though.

Answer 1

Minimum Code Requirement and the Problem with Uneven Lighting

It seems like you're trying to correct for what is likely minimum code requirement wiring. Usually that means a single electrical box for a light fixture in the middle of a room, or a switched outlet ostensibly for floor lamps. The problem with this minimal number of fixtures is twofold:

1. As you identified, there are entire parts of the room that will be in a shadow because light travels in a straight line. You'll get some reflections off of the walls and other objects in the room, but that will generally be at a loss on the order of 10x.

2. The intensity of light from a fixture that falls on an object is roughly proportionate to the inverse cube of the distance from the light. This means that an object 9 feet from the fixture has approximately 1/27 the light falling on it as does an object 3 feet from the fixture.

The above two problems can be summarized as uneven lighting. The trouble with uneven lighting is that your eye will adjust to some sort of average of the brightness. The single bright light in the middle of the room is probably way brighter than that average, so it becomes uncomfortably bright to have in your field of vision. At the other extreme, the shadows are likely much dimmer than average, so your eyes will likely just see dark.

Both of the above problems are lessened by increasing the number of light fixtures.

How Many Fixtures Do You Really Need? Experiment!

To achieve even lighting, you need way more fixtures than minimum code requirement. My last renovation included one light fixture for every 25 square feet on average which represents about 5 times the number of fixtures that were originally installed. That's just about what is minimally necessary if you want to avoid both shadows and having bright bulbs within your line of vision.

Of course, the ideal number of fixtures depends on your room shape, light fixture design, wall, ceiling, and floor colors and material, and a bunch of other things. Accordingly, I found that it is best to experiment with your space before electrical rough-in by mocking up the fixtures and trying them out in the location to make sure you're happy with the result. For the experiments to be meaningful, you really need to have multiple fixtures so that you can evaluate how their lighting adds in the room. During renovations, I usually just screw a bunch of fixtures on cords to the original walls and ceiling drywall and see what happens. If you're trying to preserve your finishes, you'll need to get more creative -- I've used tripods and photography light stands before too.

Answer 2

You have a number of issues affecting the poor lighting in the mirror. When light hits you when facing the mirror it's reflected light coming off the ceilings, walls and other items in the room.

The intensity of light falls off exponentially following the inverse square rule. When you double the distance the intensity of light is 1/4th. Triple the distance it's 1/9th as strong.

The closer you are to the light source the more intense the light will be. Reflected light not only loses intensity because your walls aren't mirrors but because it also has a greater distance until it reaches you.

More lights provide more even illumination and you can theoretically get away with much lower total lumens than if you used a single bulb.

Edit: Here are some more details to illustrate the point. Assume you have a 10'x10' room currently illuminated with 1 light source in the center of the room. You want to replace that single fixture with 4 lights instead. Each at 1/4 the power of the first light.

We start with 1 light with a power of 1 unit that is 60" away from the mirror and delivers a light intensity of 1 at the mirror.

We replace it with 4 lights that are each 1/4 the power of the first unit. Two lights are about 42.426407" away from the mirror and two lights are 94.875" away.

The intensity of the closer lights are: (60/42.426407)^2 * 0.25 (for reduced wattage) = ~0.5 Half of the original intensity

The intensity of the 2 lights furthest away is (60/94.875)^2 * 0.25 = ~0.1 of the original intensity.

Add up the 4 lights: 0.5 + 0.5 + 0.01 + 0.01 = 1.2

So you're getting roughtly 20% more direct light than you were with the one bulb. With the given placement you're also not blocking the light by standing between the light and the mirror.

Answer 3

You basically have the right idea.

LEDs don't throw much heat (they do throw some, but not all that much) so overheating the room with the lights is probably not much of a concern.

I'd encourage you to look at LED fixtures rather than LED bulbs to go into sockets, especially since you are putting on new fixtures anyway. A series of compromises are made to create an LED bulb that goes into a socket like an incandescent bulb. An entire fixture deigned as an LED fixture can avoid some of those compromises.

Answer 4

Multiple bulbs will give you a perceived increase in brightness, for the same amount of lumen.

When choosing LED, pay attention to the beam angle.