The watts per metre on a Hi-Line strip is the most that strip can draw. We measure a short length at the full stated voltage, before the voltage falls along the copper. That number is what the driver and the cable are sized for. A meter on a long reel often reads less. The strip has not been overstated. The far end is no longer at the full supply voltage, so it cannot take the full current.
A 5 metre Premium 528 reel, fed at both ends
The Premium high-brightness strip, 528 LEDs per metre, is specified at 15 W per metre on 24 V. In the workshop a 5 metre reel was powered at both ends together, so both ends sat at the supply voltage and the voltage drop was as small as that arrangement allows. No extra feed was added along the reel. The meter read 2.6 A at 24 V.
2.6 A × 24 V is 62.4 W for the reel, which is 12.48 W per metre. We do not print 12.48 W per metre as the specification. That reading belongs to one test: five metres, fed from the two ends only.
The copper loses voltage as the current travels. LEDs away from the feed are not at a full 24 V, so they draw less and give less light. A little of the power the supply does deliver is lost as heat in the tracks. The watts that never appear on the meter were not drawn at all. They are not a hidden load, and they are not a fault in the reel.
A short piece does not have that loss. Half a metre, connected properly, can draw the full 15 W per metre. The same 5 metre reel with power taken in at more points along its length also loses less voltage, so the current rises above 2.6 A and the light comes up, towards the 15 W per metre limit. It will not draw more than 15 W per metre.
If the listing said 12.48 W per metre, a driver chosen from that figure would be too small as soon as the run was shorter, or as soon as extra feed points were added. Size the supply for 15 W per metre of this strip. At 24 V that is 0.63 A per metre. Five metres is 75 W. Allow the usual headroom on the driver on top of that.
This is the open Premium reel, for example the 5 metre 2700K version. It is not the Cut Anywhere strip below, and it is not a 12 V 528 reel.
Cut Anywhere is a different 528
The Cut Anywhere COB also has 528 LEDs per metre. It is a different strip, specified at 11.5 W per metre on 24 V, which is 0.48 A per metre. The same rule applies. A short length at a full 24 V is the maximum. A 5, 10 or 20 metre reel fed from the ends draws less than 11.5 W per metre, and the far end is dimmer. It will not draw more than 11.5 W per metre.
This COB is a standard-efficiency strip. Set against another standard COB of the same type, the higher wattage is the brighter one. Do not compare its meter reading with the Premium 15 W reel, and do not expect them to look the same.
The 12 V 528 strips are a third design
The 12 V reels with 528 LEDs per metre are designed for about 8 W per metre, and not above 10 W per metre. That limit is the design of those strips. Do not size them as a 15 W reel, and do not treat a low reading on a 24 V Premium reel as if it were one of these 12 V strips.
Fewer watts can be the same light
Watts are not a ranking of brightness between different strips. A high-efficiency strip can give the same light from about half the power. As an illustration, 10 W per metre of a high-efficiency strip can match the light of 20 W per metre from an ordinary strip of the same type. The meter reads less because the chips turn more of the power into light. That is not a short measure, and it is not a reason to return the reel.
Hi-Line says on the listing when a strip is a high-efficiency design. Not every strip in the shop is an ultra-high-efficiency strip. Where the listing does not say so, use the stated watts as the figure for that strip, and use the standard-efficiency comparison only against another strip of the same type.
The chips on these reels are chosen for colour, life and efficiency. A still more efficient strip can be made for a project when the quantity is enough for a production run. Email the length, the colour and the light level you need, and we will say whether that run can be made.
If your meter reads low
Write down the length, where the power is connected, and the voltage at the far end. A long reel fed only from the ends will sit below the stated watts per metre. A short length at the full voltage should be close to the stated figure, and it should not go above it. If a short piece at the correct voltage draws more than the stated watts per metre, email us with the length and how it was connected.
