1. Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps. 

2. As street-lights, sodium lamps have longer life span than LED lamps. 

3. The spectrum of visible light from sodium lamps is almost monochromatic while LED  lamps offer significant colour advantages in street lighting. 

Select the correct answer using the code given below 

(a) 3 only 

(b) 2 only 

(c) 1 and 3 

(d) 1, 2 and 3 

Ans: c 

Explanation:

LEDs emit light in a specific direction, reducing the need for reflectors and diffusers that can trap light. The light of sodium vapor lights is omnidirectional, 360 degrees of light are produced using omnidirectional lighting. LED lights produce 180 degrees of light. Since light is frequently needed over a target region, this is usually advantageous (rather than all 360 degrees around the bulb).

Hence, statement 1 is correct.

Compared to all other lighting technologies, LEDs have a very long lifespan. New LEDs have a lifespan of at least 100,000 to 150,000 hours. So the lifespan of LED street lights is also very long. Sodium lamps fall well short of LEDs in lifespan, its life span is 18000 hours. 

Hence, statement 2 is incorrect.

A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce monochromatic light at a characteristic wavelength near 589 nm. Two varieties of such lamps exist: low-pressure and high-pressure. 

LEDs can emit light in a range of colours. A mix of red, green, and blue LEDs is sometimes used to make white light. 

Hence, statement 3 is correct.

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