1. (a) A 60 m × 50 m cargo handling area (Figure Q1.1) requires an average maintained illuminance of 50 lux. The floodlight with data given in Figure Q1.2 is selected for the illumination of this area. Six 15 m poles are built on both 60 m sides offset by 5 m from the edge of the area (Figure Q1.1). The peak intensity of the luminaires is aimed at a point 2/3 across the width of the area. Calculate the number of luminaires required on each lamp pole (all lamp poles have the same number of luminaires). Given the following data: Initial flux output of the 400W high pressure sodium lamp = 48,000 lm Lamp lumen maintenance factor LLMF = 0.85 Luminaire maintenance factor LMF = 0.8 Atmospheric loss factor = 1.0 Assume lamp is replaced immediately when it fails (b) With the number of luminaires calculated in (a), calculate: (i) the average maintained illuminance on the area (ii) the maintained illuminance at the centre of the area (iii) the maintained illuminance at the corners of the area
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Sheet - Illumination 1. A room of size 10 x 4 m is to be illuminated by ten 150-W lamps. The MSCP of each lamp is 300. Assuming a depreciation factor of 0.8 and a utilization factor of 0.5. Find the average illumination produced on the floor. 2. The front of a building 25 x 12 m is illuminated by 20 1,200-W lamps arranged so that uniform illumination on the surface is obtained. Assuming a luminous efficiency of 30 lumens/W and a coefficient of utilization of 0.75. Determine the illumination on the surface. Assume DF = 1.3 and waste light factor 1.2. 3. The luminous intensity of a lamp is 600 CP. Find the flux given out. Also find the flux in the hemisphere containing the source of light and zero above the horizontal. 4. A room with an area of 6 x 9 m is illustrated by ten 80-W lamps. The luminous efficiency of the lamp is 80 lumens/W and the coefficient of utilization is 0.65. Find the average illumination. 5. A factory space of 33 m x 13 m is to be illuminated with an average illumination of 72 lm/m2 by 200 W lamps. The coefficient of utilization is 0.4 and the depreciation factor is 1.4. Calculate the number of lamps required. The lumen output of a 200-W lamp is 2,730 lm. 6. The front of a building 35 x 18 m is illuminated by 15 lamps; the wattage of each lamp is 80 W. The lamps are arranged so that uniform illumination on the surface is obtained. Assuming a luminous efficiency of 20 lumens/W, the coefficient of utilization is 0.8, the waste light factor is 1.25, DF = 0.9. Determine the illumination on the surface.
Adi S.
1. A high-pressure mercury-vapour lamp is mounted at a height of 6 m in the middle of a large road crossing. A special reflector directs 100 C.P. maximum in a cone of 70° to the vertical line. Calculate the intensity of illumination on the road surface due to this beam of 100 C.P. (Electrical Engineering, Bombay Univ.) 2. A room 6m × 4 m is illuminated by a single lamp of 100 C.P. in all directions suspended at the centre 3 m above the floor level. Calculate the illumination (i) below the lamp and (ii) at the corner of the room. (Mech. & Elect. Engg. : Gujarat Univ.) 3. A lamp of 100 candle-power is placed at the centre of a room 10 m × 6m × 4 m high. Calculate the illumination in each corner of the floor and at a point in the middle of a 6 m wall at a height of 2 m from the floor. (Utilization of Elect. Power A.M.I.E.) 4. A source of 5000 lumen is suspended 6.1 m. above ground. Find out the illumination (i) at a point just below the lamp and (ii) at a point 12.2 m away from the first, assuming uniform distribution of light from the source. [(i) 10.7 lux (ii) 0.96 lux] (A.M.I.E. Sec. B) 5. Determine the average illumination of a room measuring 9.15 m by 12.2 m illuminated by a dozen 150 W lamps. The luminous efficiency of lamps may be taken as 14 lm/W and the co-efficient of utilisation as 0.35. [79 lux] (A.M.I.E. Sec. B) 6. Two lamps are hung at a height of 9 m from the floor level. The distance between the lamps is one metre. Lamp one is of 500 candela. If the illumination on the floor vertically below this lamp is 20 lux, find the candle power of the lamp number two. [1140 candela] (Utili. of Elect. Power A.M.I.E.)
Sri K.
Analyze We begin by determining the magnitude of the beam's Poynting vector. Divide the time-averaged power delivered via the electromagnetic wave by the cross-sectional area of the beam: Savg = Pavg / A = Pavg / (πr^2) = (2.7 × 10^-3 W) / (π((1.9 × 10^-3 m)/2)^2) = 952 W/m^2 Analyze Now let's determine the radiation pressure from the laser beam. The equation for radiation pressure exerted on a perfectly reflecting surface indicates that a completely reflected beam would apply an average pressure of Pavg = 2Savg/c. We can model the actual reflection as follows. Imagine that the surface absorbs the beam, resulting in pressure Pavg = Savg/c. Then the surface emits the beam, resulting in additional pressure Pavg = Savg/c. If the surface emits only a fraction f of the beam (so that f is the amount of the incident beam reflected), the pressure due to the emitted beam is Pavg = fSavg/c. Use this model to find the total pressure on the surface due to absorption and re-emission (reflection): Pavg = Savg/c + fSavg/c = (1 + f)Savg/c Evaluate this pressure for a beam that is 70% reflected: Pavg = (1 + 0.70) (952 W/m^2) / (3.0 × 10^8 m/s) Pavg = .00000539 N/m^2 Finalize Consider the magnitude of the Poynting vector, Savg = 952 W/m^2. It is about the same as the intensity of sunlight at the Earth's surface. For this reason, it is not safe to shine the beam of a laser pointer into a person's eyes, which may be more dangerous than looking directly at the Sun. The pressure has an extremely small value, as expected. (Recall from a previous chapter that atmospheric pressure is approximately 10^5 N/m^2.) A 10.0 mW helium-neon laser (λ = 632.8 nm) emits a beam of circular cross section with a diameter of 2.00 mm. (a) Find the maximum electric field in the beam. Emax = V/m (b) What total energy is contained in a 7.50 m length of the beam? U = J (c) Find the momentum carried by a 7.50 m length of the beam. p = kg·m/s
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