LED light strips - three questions

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geekIT

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#198448 9-Jul-2016 14:24

Question 1: How many lumens do the individual LEDs emit? Obviously, this will depend on the model of LED. I can describe mine if someone would tell me what designation to look for.

Question 2: How much heat per LED? Again, I guess this'll be dependent on the model.

Question 3: For various reasons I may have to use a longer strip of lights than I'd prefer. Would it be practical to dab the unwanted LEDs with a dollop of black paint?

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andrewNZ

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#1588850 9-Jul-2016 14:47

1) Don't know

2) Stuff all, cold enough to hang on to.

3) Are you sure you can't cut the strip shorter? Many strips come in 1m lengths, but can be cut down to the nearest 100mm

geekIT

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#1588887 9-Jul-2016 16:06

3) Nope, can't shorten the strip. I'm putting concealed lights into a 1400mm long cabinet and I want the whole space illuminated evenly. But I think the number of lights in a 1400mm piece will be too bright. Hence, eradicating some of them by painting them black.

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pipe60

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#1588924 9-Jul-2016 17:25

if its too bright use a dimmer to adjust.

Something like this

http://tasklighting.co.nz/Fullspec_LCDM_MAN_8A_12_24.php

geekIT

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#1589106 10-Jul-2016 11:08

P, thanks but the system is already built around an HPM trailing edge dimmer. This gizmo also has a built-in ON\OFF switch, which the linked dimmer doesn't have.

But the problem is that these LED strips don't turn off completely. By that I mean if a strip is ON but completely dimmed, the LEDs still emit light. So, if there are say, 40 or 50 LEDs in a 1400mm strip (I haven't counted them exactly), they still produce a fair bit of light when they're at minimal power.

Which isn't what I want.

I don't mind a very minor glow, but too much would defeat the purpose of this night-lit bedroom cabinet.

Hence my question about 'disabling' some of the lights.

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richms

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#1589131 10-Jul-2016 13:30

Assuming you got 5050 LEDs on the strip there are 3 LED dies in each of the square 5mm package, they are usually in series for 3 of them with a resistor per string of 3 (why you have cut marks every 3) so if you take one of the SMD resistors off per group, you will lose 1/3rd the light output, take 3 off, lose 2/3 of the light (close enough - LEDs become slightly more efficient when cool so you may lose less than the full 2/3)

Alternativly stick resistors inline with the whole string to drop the voltage furthur - you should have a watts per meter for the strip so you can figure out the current from that, which will let you know how much power the resistors will need to dissapate so you know if you should get 5w or 10w ones or more. They will get hot however when its turned up.

Light is not a linear response in your eye tho, so losing 2/3 may not make much difference, and that would also limit the max brightness. As would resisters.

Is there a minimum adjustment control on the side of the dimmer at all?

Richard rich.ms

geekIT

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#1589156 10-Jul-2016 15:42

Thanks, richms. No, there's no minimum adjustment (that I can see) on the HPM Legrand 400T Trailing Edge dimmer module.

But I've now painstakingly joined together six 3xLED clusters interspersed with 150mm cable connectors.

I was trying to avoid this because of the fiddly soldering work but it's done now and the 18 LEDs are working OK.

I'm just waiting for darkness to test the rig and see how it performs.

The only other uncertainty is whether or not I can rely on the 3M sticky tape to hold the LED sections in place in an aluminum 'u' channel.

The strip will be on the bottom, so gravity should assist, but I might add a few dollops of silicone or araldite to make sure.

Oh, and another unknown is how long the LEDs last. But I guess if one or more lights fail, the group will stay lit.

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