Help Please - Calculate "Over Time Rate" for LED Emergency Lighting

Not sure what you are asking. Are you asking how long emergency lighting will last running off battery power? If so you need to know the current draw of the LEDs and the rating of the battery in terms of amp-hours.

Go back to calculus I: the integral of current over time is charge. Charge has units of coulombs, Faradays, or millamp-hours, amp-hours, kiloamp-hours, etc.

Example: Your backup power (for emergency lighting example) has a charge rating Qr of 1 amp-hour. After level draw of current on this battery for 1 amp-hour, the potential of the supply will drop off (semi-sharply, but is not a step function). Suppose that after the rated charge is dissipated, the decline is such that supplied current has a time slope of -1. This means that δ²Q/δ²t=0; t<t(Qr), δ²Q/δ²t = -1 ; t>t(Qr), and δ²Q/δ²t = 0 ; t>t(Q=0). This is not likely to be a "real" battery. We also know that δQ/δt =I(t), current, and is constant early on, proportional to (t(Qr)-t) during roll off of potential, and at total discharge I->0 in the limit.

Suppose now that your lighting fixture has a nominal current draw of 100 mA. This means that (1) you better have good night vision because this is a weak light source, and (2) 1 amp-hour will be reached (Qr) in precisely 10 hours. With a slope factor of -1, this means that the area under the current triangle is somewhere around 1/2Qr (W.A.G.), and the time to cut out depends on two things: (a) the time until forward bias of the LED lighting fixture is no longer supplied, and (b) the time until current available is less than the critical current for minimum acceptable lumens is reached.

If the critical current is more important (and I think it is), say that is half the nominal current draw. This time increment is precisely the time required to reach Qr plus half that time, thus the time over current is time and half a time, or 15 hours.

Thanks, I could use a bonus!

Irreverence is my middle name.

Or, is it irrelevance?

I thought you were with the Redundancy Division of the Department of Redundancy?

Now here's a prideful man who will take irrelevancy to a whole new level..

Yeah but the VA is probably using Chinese knockoffs...

Yeah, we (the taxpayer) are being screwed. This is the problem when 'insurance' pays for it. If it were your 'own' money, you'd shop around and demand the best price. The other problem is that when 'insurance' pays for it, you are much less likely to even ask if you 'need' it.

Is this with or with out O'bammer care cost??

Regards Lyn. Nice one

Now,,, that all depends on what it says in your collective agreement.

You haven't also been tasked with sourcing a left-handed screwdriver have you?