# Help me figure out the lighting "ability" of bulbs and combinations of please

This may sound slightly idiotic, but help a novice if you may

Let’s say we have a 60 watt bulb and a 100 watt bulb. The 60 watt is obviously dimmer than a 100 watt. However, if we have a fixture that uses two 60 watt bulbs, it will help “brighten” the room over a single 60 watt bulb but note more than a 100 watt… or will it?

Maybe look at it this way: Which will brighten a room more effectively - Two 60 watt bulbs (or to make it interesting, lets say two 50 watt bulbs) or a single 100 watt bulb?

Two 60-watt bulbs would give the same amount of light as a 120-watt bulb, so yes, more than a 100-watt bulb. Look on the bulb package, it will tell you the average lumens, or light output.

Oh, I should mention that a 60-watt bulb gives light that is slighter redder than the light a 100-watt bulb gives. Higher wattage bulbs tend to emit whiter light, so that might be a factor to consider as well.

Here’s a nice listing of watts vs lumens for many common bulbs.
60 watters typically put out ~850 lumens, while 100 watt bulbs emit ~1600 lumens.

Here’s a nice listing of watts vs lumens for many common bulbs.
60 watters typically put out ~850 lumens, while 100 watt bulbs emit ~1600 lumens.

Also, depending on your definition of effective, you may get less shadow with 2 x 60w because you have 2 point sources, rather than one. (This depends somewhat on where the two sources are placed, obviously).

Duh. Maybe I should’ve actually read the OP before I chimed in. Sorry.

Even though a single high-wattage bulb (e.g. 100 W) may be slightly more efficient than two or more cooler bulbs with the same combined wattage, I still prefer using “multi-bulb fixtures” for the following reasons:

1. Single high-wattage bulbs are, well, hot. Why subject a lamp socket, globe, etc. to all this heat? It can’t be good on it.

2. If your fixture has one high wattage bulb, you will be fumbling around in the dark when it burns out. At least you’ll still be able to see when one bulb burns out in a multi-bulb fixture.

I had no idea that you could (more or less) simply “add” the lumens from each source. I thought it was more complex than that.

Yeah, I know the heat factor is an issue. I am in the process of replacing the incadescent lights in our home with those new-fandangled flourescents that screw in a standard socket. They’re not cheap (about \$4.50 each CDN versus about .50) but they supposidly last 10 times as long and only use a fraction (1/5) the power… so in the long run they pay off. I find they give off a slightly “pinkish” hue that is only really noticable if you have a new one and old one side by side in the same fixture.

I’ve also installed a few fluorescents bulbs in our house. I have mixed feelings about them. On the one hand they are more efficient. But on the other hand,

1. I don’t like the color of light they give off
2. They’re expensive
3. They can cause EMI
4. They’re big and bulky

Besides, the amount of power most homes use for lighting is relatively small. If you want to decrease your electric bill you should focus on improving the efficiency of the big boys (refrigerator, electric water heater, electric furnace, etc.)

We have lots of those energy saver bulbs around. They last a long time, gives off nice light (we have a variety of choices), they aren’t big and bulky, and I don’t think they emit EMI.

Good stuff.

Agreed. We have a brand new home though and have all energy effecient appliances right from the get-go. Our dishwasher, clothes washer and fridge are each highly energy effecient. Our stove, waterheater, dryer and furnace are all effecient and and also natural gas… although that has also gone up tremendously.

Well, it is, really. But if those two bulbs are in one place, then it’s a good approximation. Obviously, if the bulbs are widely separated the lighting at any one point depends upon how far away the bulbs are, and the lighting pattern from two bulbs is different from that given by one bulb.

This is the wonderful and annoying science of photometry, which has the most confusing units of any discipline (lumens, candelas, stilbs, lux, phots, foot-candles, etc.). For practical home applications, there are books on illumination and lighting engineering that can help you out. There’s even a society of lighting engineers. Heck, there are trade journals for this stuff, and they give academy awards for lighting design. It’s a big topic. You’d do best to find a few books on it.

That could turn bernse into a microeinstein of lighting theory !