How many LEDS would it take to replace a light?

[prisoner1572]

I am trying to get the same light output from LEDs that I can get out of a 100 watt fluorescent light. The problem is that its so confusing with all the different ways they rate lighting. How many candelas does a fluorescent light like this put out. Or how many LEDs would I need of a certain mcd rating?

 

[Doug Owen]

Typical fluorescent light outputs are on the order of 40 Lumens/Watt, for top end LEDs it's about 20 per.

So for the same light as a typical 100 Watt fluorescent Lamp, you'll need say 40 high bin 5 Watt LSs......

Doug Owen

 

[idleprocess]

Re: How many LEDS would it take to replace a light

It's not practical to replace high-power lamps of any flavor with LEDs. Generally, LEDs aren't as efficient as incadesent lamps at voltages greater than a typical flashlight.

Luxeons are expensive, and the other high-power LEDs don't seem to be substantially better - at least one is worse!

Occasionally, you'll see a 3/5mm LED that puts out almost 1 lumen. Go a bit more exotic, like a 80mA SMD LED or a multi-die 8/10mm LED, and you might get up to 6 lumens.

I work for a manufacturer, and we buy 20-watt, 18" floresent tubes for ~$1 each, rated at 750 lumens. Toss in a cheap ballast, cheap starter, and some expensive custom sheet metal to reflect the light, and you're at clost to $40 - still substantially less than the cost of 750 lumens worth of LEDS!. Toss in a PCB, driver circuitry, and thermal maganement issues of that many LEDs and suddenly there's no justification for going solid-state because the energy/labor savings don't save any money during the unit's operational lifespan.

I'm not trying to dissuade you from experimenting with LEDs to replace disposable floresent tubes - I just want to give you some perspective on what you're proposing.

 

[idleprocess]

Re: How many LEDS would it take to replace a light

Also, candelas are a deceptive measurement... they're a measure of intensity, not total output like lumens.

A candela value without beam angle is meaningless, since you don't know what area is being covered. For example, a 6400 mcd LED @ 20 degrees is about half as much light as 280 mcd over 140 degrees.

If you see a really high candella (or mcd) value without a beam angle, odds are it's a narrow beam angle since any relatively dim light source can be made intense at a narrow angle.

There are ways to approximate lumens from mcd x beam angle - several are discussed in this thread.

 

[Josey]

Re: How many LEDS would it take to replace a light

I use an LED (36 5mm bulbs) for a reading light. It's perfect for that because it's directional and it lights up only what I am reading, not the whole room.

It's using about 200 milliamps (as read on my wall mounted Trimetric, which has resolution only to 100 milliamps). My battery bank is reading 12.3 volts (it's a solar system), so my reading light is using 2.46 watts.

Above me is a 26 watt compact fluorscent light (.4 amps times 116 volts from my Trace inverter), which is equivalent to a 100 watt incandescent light.

I could put a light meter on it, but I can easily tell that the 26W CFL is not as bright as my 2+watt LED, at least on the surface of my desk. It may well have many more total lumens, but most of them are bouncing to other places in the room where I don't need them.

LED reading lights made my solar system practical in the rainforest, where in the winter the sun is mostly a memory.

 

[idleprocess]

Re: How many LEDS would it take to replace a light

Josey:

If your LED-array reading lamp were trying to light up an entire room, would it do as good a job as the compact floresent? I doubt it. I imagine you get more mileage from your CFL light than you're giving it credit (whenever you're not at your desk, anyway).

Having lived on the Oregon coast in my youth, I remember the near-constant rain in the winter. Seems that a wind turbine might be a bit more practical - or at least a good way to augment your solar array.

 

[Negeltu]

Re: How many LEDS would it take to replace a light

I think his point was that he gets more light in the spot that he reads from the leds than from the flourescent. I don't see where he was trying to say that the leds were better for room lighting.

 

[3rd_shift]

Re: How many LEDS would it take to replace a light

It would appear that higher output lighting should not be in any danger of getting replaced by leds any time soon.

But look how far leds have come in the last 5 years.
Remember when we used to marvel at $5-$10 t5 whitish ones then?
Those weren't even half as good as the t5s we have available today for way less.

 

[idleprocess]

Re: How many LEDS would it take to replace a light

Radio Shack still thinks that there's a market that marvels at $6 5mm white LEDs...

 

[Doug Owen]

Re: How many LEDS would it take to replace a light

[ QUOTE ]
idleprocess said:
Radio Shack still thinks that there's a market that marvels at $6 5mm white LEDs...

[/ QUOTE ]


Actually, they can *prove* there's such a market....they're catering to it.....

Doug Owen

 

[3rd_shift]

Re: How many LEDS would it take to replace a light

Most of that market hasn't yet seen www.lsdiodes.com or
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