Lumen Outputs from Lamps

Light measurement figures are mostly bunkum and difficult to measure or comprehend.
Del

Placing a luminosity measuring-device near the source will give more than double the reading than if it was placed a meter or two away.

Light intensity decays with distance.

Besides, light for application purposes is given as ambient measurement of reflected or diffused. measuring directly at the source will give an unrealistic result of measurement.

You can buy an old CDS light-meter from olf photo equipment shops, and measure and compare measurements with other lamps, in various conditions. Set the meter to the widest apperture and keep the scale at the same point - to have a steady reference point.

CDS meters require no batteries, their energy is drawn by the light you measure.

400W refers to the input power.

As regards the lumens, why not go for 90?

<....is the input power to the lamp or is it the output power from the lamp....>

It is the electrical load, the input power, for supply sizing purposes. The output power will be the same, though it will be distributed between light and heat.

<...lumens per watt...>

This is the effectiveness of the light source, i.e. the amount of light produced for each unit of electrical power consumed. In general terms, tungsten incandescent lamps have a lower effectiveness than, say, LED lighting, though there are a number of factors to consider before carrying out design selection or installation substitution. Among them are the light's "colour temperature" and its beam angle.

First of all in reply to Yuval: lumens is a measure of the total light output; lux is the measure or light intensity which decreases the further you are from the light source.

Second I don't know anything about this so I'm just guessing: look at this Wikipedia article on Luminous efficacy. I suspect that the "missing" ~20 lumens is radiated outside the visible spectrum.

By "Luminosity measuring device" I didn't specifically refer to "Lumen Meter", but instead to any light intensity measuring device.

My point was that

1. light has a source with given intensity

2. light intensity decays with distance

3. reflected light keep bouncing from one surface to another, which is why photographers measure ambient light with an opal (diffused) meter - to get an average all-round intensity.

So, measuring light intensity requires a definition of what exactly do you intend to measure - it is complicated, and it has wide range of specific results, according to your intended measurement.

OK.

The point is that the OP is trying to figure out how the lamp manufacturer can specify two different values for lumens/Watt.

If it is a straight forward manufacturer (and let's face it: some are not), they should specify the conditions in which they took their resulted measurement, so that such a question would not arise in the first place

I recommend you look into IEEE Spectrum Magazine August 2009 edition. I am sure its on line somewhere. Anyway its lead story is "The LED's Dark Side" it should give you some answers and insight.

I suspect the two different lumen for watt values (source & application) refer to the power entering the fixture (source) and the power entering the LED lamp (application). Unlike a filament lamp, LED light sources cannot handle line voltages directly. The added losses are whatever conditioning circuitry the manufacturer has selected. But this is only a guess on my part. To find out the real answer you'll have to contact the manufacturer.

What exactly are you trying to do?

I deal with LED Lighting every day of my life, build new lights, test others, etc.

I come from a more practical point of view, that is, if it works, fine, if it doesn't, do something different..

I normally use a light meter to test the lux, or foot candles of a light source, at the point where it will be used.

Many times I find that what I learned while visiting Germany, many years ago work well. That is, move your light source closer the the area needing the light.

This way you can avoid lighting unecessary areas..

Another I have learned about LED Lighting is: The warmer the color temperature, the less lumen output you have.. which seems strange to me, because with fluorescent, it's just the opposite..

just some thoughts..

Donald

"...warmer the color temperature, the less lumen output you have..." - It only makes sense: the shorter the wavelenght, the higher the enregy, or "penetrability"

I'm not sure on their exact usage of source and application, but I assume that source is the total light energy output. This is generally measured by placing the light into an integrating sphere (a sphere painted with a diffuse white coating, usually TiO2) with a light meter. The application is the light that makes it to the area where the light is pointed. The rest of the light is either absorbed by the optics, or sent out of the illuminated area. Take a look at a halogen bulb and you will see a lot of light that gets out to the side, LED's are similar. The diode emits in a cone, and the optic afterward can not send all the light to the desired area.

The watts reading as other entries have stated, is the input power. This changes depending on the input type; i.e. 120V AC will have a lower efficiency as 5V DC because electronics are needed to convert the AC to DC and drop the voltage.

hope this helps.

oh, and some terminology

The source has an intensity a given distance away, and the receiver has an irradiance. Both measured in W/cm^2, or lux and is the amount of light energy over an area; 1 Lux=0.001496 W/m^2. Where the total energy emitted is measured in Watts or lumens; 1 lumen=0.001496 W.