Convert 7.8 watts into lumens

Answer 1

You cant convert directly between Watts and Lumens. They are measuring completely different things.

Lumens measure the flux of a light being produced by a light source or received by a surface, while Watts measure the amount of power used.

You could have a higher power device, but with less light then a low power one. It just depends on the light.

Unless the flashlight manufacturer already has the Lumens and Watts listed, you won't be able to find out.

Answer

The watt is the radiometric unit for power, whereas the lumen is the photometric unit for power. In the case of a lamp, the watt is the product of the supply voltage and load current drawn by the lamp and describes the power input to the lamp. The lamp's power output is termed 'luminous flux' and the amount of luminous flux produced by a lamp depends upon it efficacy (NOT 'efficiency'), which is the ratio of input power expressed in watts to the luminous flux (i.e. output power) expressed in lumens -i.e. watts per lumen.

The efficacy of a lamp depends upon the type of lamp -i.e. its principle of operation. Generally, incandescent lamps have relatively low values of efficacy, whereas fluorescent or other 'energy efficient' (e.g. LED) lamps have relatively high values of efficacy.

To answer your question, it is necessary to know the typeof lamp to which you refer. In the absence of that information, I suggest that you search for 'efficacy of lamps' on the internet, in order to determine the efficacy of your particular lamp. Once you know that, you simply then multiply that efficacy by the number of watts (7.8) in order to determine the number of corresponding lumens.