Advertisements
Advertisements
Question
A light source emits monochromatic light of 555 nwavelengthm. The source consumes 100 W of electric power and emits 35 W of radiant flux. Calculate the overall luminous efficiency.
Advertisements
Solution
Given:
Wavelength of light, λ = 555 nm
Radiant flux emitted = 35 W
Power input = 100 W
Overall luminous efficiency = `"Total luminous flux"/"Power input"=(35xx685)/100=239.75 "lm/W"`
So, the overall luminous efficiency will be 240 lm/W.
APPEARS IN
RELATED QUESTIONS
The luminous flux of a 1 W sodium vapour lamp is more than that of a 10 kW source of ultraviolet radiation. Comment.
A bulb is hanging over a table. At which portion of the table is the illuminance maximum? If a plane mirror is placed above the bulb facing the table, will the illuminance on the table increase?
The sun is less bright at morning and evening as compared to at noon although its distance from the observer is almost the same Why?
Why is the luminous efficiency small for a filament bulb as compared to a mercury vapour lamp?
The one parameter that determines the brightness of a light source sensed by an eye is ____________ .
As the wavelength is increased from violet to red, the luminosity ____________ .
The intensity produced by a long cylindrical light source at a small distance r from the source is proportional to _________ .
A point source of light moves in a straight line parallel to a plane table. Consider a small portion of the table directly below the line of movement of the source. The illuminance at this portion varies with its distance r from the source as ___________ .
Figure shows a glowing mercury tube. The intensities at point A, B and C are related as __________ .
A room is illuminated by an extended source. The illuminance at a particular portion of a wall can be increased by
(a) moving the source
(b) rotating the source
(c) bringing some mirrors in proper positions
(d) changing the colour of the source.
Using figure, find the relative luminosity of wavelength (a) 480 nm, (b) 520 nm (c) 580 nm and (d) 600 nm.
The relative luminosity of wavelength 600 nm is 0.6. Find the radiant flux of 600 nm needed to produce the same brightness sensation as produced by 120 W of radiant flux at 555 nm.
The luminous flux of a monochromatic source of 1 W is 450 lumen watt−1. Find the relative luminosity at the wavelength emitted.
A student is studying a book placed near the edge of a circular table of radius R. A point source of light is suspended directly above the centre of the table. What should be the height of the source above the table so as to produce maximum illuminance at the position of the book?
Two light sources of intensities 8 cd and 12 cd are placed on the same side of a photometer screen at a distance of 40 cm from it. Where should a 80 cd source be placed to balance the illuminance?
Photo diodes are used to detect ______.
