# How to properly read Watt of a bulb power?

I'm confused about reading the terms Watt, Wh, and Ws of bulbs. Here is the quoted text taken from an electrical book that I'm currently reading on : Now I'm take out some points from the remarks that confuses me:

1. 60 W-bulb consumes 60 Wh in 1 hour.
2. 100 W-bulb consumes 1 Wh in 1/100 hour.

My questions are :

1. Why does a 100-w bulb consume 1 Wh in 1/100 hour, instead of 100 Wh in 1 hour? (Like that one in the case of 60-W bulb)
2. Is 60-Wh equivalent to 60*3600 Watt in a second?
• 1. 1 Wh in 1/100 hour and 100 Wh in 1 hour are the same thing ............ 2. think about what you are asking ... 60Wh = 216000W in a second .... i don't think so ....... if you fill 60 buckets with water in 1 hour, then how many buckets will you fill in 1 second? – jsotola Aug 1 '18 at 7:21
• Hi your #2 makes sense. I'm sorry it is my confusion, like saying 1 km = 1000 m. Anyway could you answer that so I can mark it on. Sorry for such retarded question. – Plain_Dude_Sleeping_Alone Aug 1 '18 at 7:29

Why does a 100-w bulb consume 1 Wh in 1/100 hour, instead of 100 Wh in 1 hour?

You are correct that 100 W for 1 hour is 100 Wh. If you divide by 100 you find that 1 Wh will be consumed in 1/100 h. If your energy meter LED blinks once per watt-hour then it should blink every 36 s if your 100 W lamp is the only load.

Is 60-Wh equivalent to 60 * 3600 watt in a second?

We don't say "watts in a second" as the watt is power which doesn't have a time factor. Energy does, however, and energy is power by time so we can have Ws (joules / J) or Wh or kWh (common for energy billing).

Your maths is correct but your units are wrong. 60 Wh is equal to 60 * 3600 Ws (watt-seconds).

Note that SI units named after a person have their symbols capitalised but are lowercase when spelled out. 'A' for ampere, 'V' for volt, 'W' for watt, 'K' for kelvin (as opposed to 'k' for kilo), etc.

• +1 for the info about capitalisation – Alexander von Wernherr Aug 1 '18 at 8:24
• You might point out that "equivalent to 60*3600 watt in a second" is not actually meaningful. 60*3600 Ws (216,000 joules) can be dissipated "in" a second, but this says little about the average power, only requiring that the peak power be greater then 216,000 watts. However, 60*3600 watts FOR one second does specify 216,000 J, which is equal (not equivalent) to 1 Wh. – WhatRoughBeast Aug 1 '18 at 13:42
• @What: I've changed "equivelant" to "equal", thanks. – Transistor Aug 1 '18 at 13:50