How to roughly infer the luminous flux of a lamp by point illuminance?

How to roughly infer the luminous flux of a lamp by point illuminance?

Yesterday, Liu asked me a question: a 6 watt lamp, a meter of illumination 1900Lx, then the luminous flux is less lumens per watt? this It was hard, but I did give him an answer, and it wasn’t necessarily the right answer, but the derivation was kind of interesting.

Now let’s talk about how to derive it.

As we all know, the simplified formula for calculating point illumination is:

E — point illumination

I — Maximum light intensity

h – The distance between the luminaire and the calculation point

With the above formula, we can obtain the maximum light intensity of the lamp under the assumption that the lamp is illuminated vertically at the calculation point. As said in the above conditions, the illuminance at 1 meter is 1900lx, then the maximum light intensity can be calculated to be 1900cd.

With the maximum light intensity, we still lack one of the most important conditions, that is, the light distribution curve, so I asked the beam Angle of the light distribution curve, and used other ways to find a light distribution curve with the same beam Angle. Of course, there are many kinds of 24° light distribution curves, and it is possible for the curves to be tall, thin and fat, and I am looking for the most perfect 24° curve.

Figure: Light distribution curve at a beam Angle of 24°

Once found, we open the light distribution curve with notepad and find the part of the light intensity value.

Figure: The light intensity value of the light distribution curve

The light intensity value is copied into EXCEL, and then the formula is used to calculate other light intensity values when the maximum light intensity value is 1900.

Figure: Using EXCEL to calculate other light intensity values when the maximum light intensity is 1900cd

In this way, we get all the adjusted light intensity values, and then replace the adjusted light intensity values back to Notepad.

Figure: Replace the original light intensity value in notepad with the adjusted light intensity value

Done, we have a new light distribution file, we will import this light distribution file into DIALux, we can get the light flux of the whole lamp.

Figure: The whole light flux of 369lm

With this result, let’s verify that the illumination of this lamp at 1 meter is not 1900lx.

Figure: The point illumination at 1 meter is 1900lx according to the cone diagram

OK, the above is the whole derivation process, not very rigorous, just provide an idea, can not be very accurate, because in the middle, whether it is the acquisition of illuminance or the derivation of light distribution, can not be 100% accurate. Just to give everyone a Estimation skill.

from Shao Wentao – Bottle sir Light