Hobbies · Dollhouse and miniatures
Dollhouse LED lighting calculator.
Enter the supply voltage, LED colour and how many LEDs you want, and the calculator splits them into series strings, picks a resistor for each string and estimates battery life. For low-voltage battery lighting only. Example: 8 red LEDs at 10 mA on a 9 V alkaline battery make three strings (3, 3 and 2 LEDs) with 330, 330 and 560 ohm resistors, draw about 27 mA in total and run for roughly 23 hours.
Your numbers
Result
Working out the result.
How the LED plan is calculated
An LED does not limit its own current, so each series string needs a resistor. With n LEDs of forward voltage Vf in series on a supply Vs, Ohm's law across the resistor gives R = (Vs − n × Vf) / I. The calculator finds the most LEDs that leave at least your chosen headroom across the resistor, splits your LEDs as evenly as it can into that many strings, and rounds each resistor up to the next E12 value (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and their multiples of ten, from the IEC 60063 preferred-number series), so the real current never exceeds your target. Total current is the sum over the strings.
Forward voltages come from Vishay's 5 mm LED table: the red TLHR5400 is listed at 2.0 V typical at 10 mA, the yellow TLHY5400 at 2.4 V, the green TLHG5420 at 2.1 V. The white VLHW5100 lists only a 3.6 V maximum at 20 mA, so 3.6 V is used for white as a cautious value, and it will give a slightly lower current than you ask for. Battery life is capacity divided by current, using the capacity chart in Energizer's 522 datasheet read at 25, 100, 300 and 500 mA (about 625, 480, 370 and 310 mAh, read off the bar chart, so approximate), measured as continuous discharge to 4.8 V at 21°C. Below 25 mA the 25 mA figure is used.
Worked examples with real numbers
- 8 red LEDs, 9 V, 10 mA each. With 1.5 V of headroom, 3 red LEDs (6.0 V) is the most per string. Eight LEDs make strings of 3, 3 and 2. The 3-LED strings need (9 − 6.0) / 0.010 = 300 ohm, rounded up to 330 ohm for 9.1 mA. The 2-LED string needs (9 − 4.0) / 0.010 = 500 ohm, rounded up to 560 ohm for 8.9 mA. Total 27.1 mA, so about 617 mAh / 27.1 mA = 23 hours.
- 6 white LEDs, 9 V, 20 mA each. At 3.6 V only 2 fit per string with 1.5 V headroom (7.2 V), so 3 strings of 2. Each needs (9 − 7.2) / 0.020 = 90 ohm, rounded to 100 ohm for 18 mA. Total 54 mA, about 10 hours.
- 30 red LEDs at 20 mA on one 9 V battery. Ten strings of 3 with 150 ohm each, 200 mA total. The datasheet chart shows roughly 410 mAh at that drain, so about 2 hours. A 9 V alkaline is a poor fit for a lot of LEDs.
Why lights can flicker on a small battery
In a July 2023 thread on the Core Electronics forum, a builder with 9 LEDs on a 9 V battery in four parallel circuits found the lights flickered when the two flicker LEDs from tea lights were connected, and worked once those were removed. One reply suggested the flicker LEDs impose a sudden extra load the battery cannot supply at once, causing a momentary voltage drop that makes the other lights flicker, adding that a 9 V alkaline probably has a high internal resistance. The builder later reported that without the flicker LEDs the lights faded out after about 10 seconds. Another reply suggested a 6-AA holder as a higher-current 9 V supply with lower series resistance. That is forum advice from two people, not a measurement, so treat it as a tip to try.
What this calculator leaves out
It plans one colour of LED on a battery or other low-voltage DC supply. It does not model mixed colours on one string, flicker or colour-change LEDs with built-in chips, LED strips with their own resistors, coin cells, or mains-powered lighting. Forward voltage varies between parts and with current, and falls with temperature, so measure a prototype. Never connect dollhouse lighting to mains power; use batteries or a purpose-made low-voltage transformer system.
Common mix-ups
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Often assumedA 9 V battery gives the same power until it is flat.
What the source saysEnergizer's 522 datasheet shows capacity measured to a 4.8 V cutoff dropping with the current drawn: roughly 625 mAh at 25 mA but about 310 mAh at 500 mA on the bar chart. Voltage also falls as it drains, which is why this tool keeps headroom across each resistor. [1]
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Often assumedLEDs of different colours can share one resistor on a 9 V supply.
What the source saysVishay lists different forward voltages by colour: 2.0 V typical for the red TLHR5400, 2.1 V for the green TLHG5420 and 2.4 V for the yellow TLHY5400. Each colour drops a different voltage, so the resistor value that sets the current differs. [2]
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Often assumedIf a circuit works on its own it will work in parallel with the others on the same battery.
What the source saysIn the Core Electronics thread each series worked alone but the lights flickered when all were connected. A reply put it down to a sudden extra load and a 9 V alkaline's high internal resistance; the builder's fix was a separate 3 V battery for the flicker LEDs. [3]
- Energizer 522 (9 V alkaline) product datasheet
- Vishay: 5 mm LEDs (forward voltage table)
- Core Electronics forum: Dollhouse LEDs (July 2023)
Checked against these sources on .
Frequently asked questions
How many LEDs can I run on a 9V battery?
As many as you like in principle, but each LED you add uses current, and a 9 V alkaline lasts far less at high current. At 10 mA each, 8 red LEDs draw about 27 mA in this plan and run roughly 23 hours; 30 LEDs at 20 mA draw 200 mA and last about 2 hours.
Do I need a resistor for every LED?
You need one per series string, not per LED. Three red LEDs in series on 9 V share one resistor. LEDs wired in parallel each need their own, or each parallel branch does.
Why does the calculator leave 1.5 volts across the resistor?
It is our design choice, not a datasheet number. A battery's voltage falls as it discharges, and a resistor with little voltage across it makes brightness swing more. You can change the headroom: less allows more LEDs per string but a less steady current.
Why is white handled differently?
The Vishay listing for the white 5 mm LED gives only a maximum forward voltage, 3.6 V, with no typical value. The calculator uses that cautious figure, so real current will be slightly higher than planned if your LED drops less. Enter your own forward voltage if you know it.
Why do my dollhouse lights flicker on a 9V battery?
One forum reply to a builder with this problem pointed to sudden extra current from flicker LEDs and the high internal resistance of a 9 V alkaline. A higher-current supply such as a 6-AA holder was suggested. Check a prototype on your own parts.
Is it safe to power a dollhouse from the wall?
Do not connect dollhouse lighting to mains power. This page is only for battery or other low-voltage DC supplies. For wall power use a purpose-made low-voltage transformer system sold for that.
Sources
Retrieved
- Energizer 522 product datasheet — nominal 9.0 V and the capacity-versus-discharge chart to 4.8 V at 21 C (read 2026-10-26)
- Vishay 5 mm LEDs table — forward voltage for TLHR5400, TLHY5400, TLHG5420, TLDR5400 and VLHW5100 (read 2026-10-26)
- Core Electronics forum: Dollhouse LEDs — builder report and replies on flickering on a 9 V battery (read 2026-10-26)
Low-voltage battery lighting only, never mains
A planning aid, not a safety certification. Battery capacity is read off a chart and is approximate. Check each LED's own datasheet, use a resistor power rating above the figure shown, and never connect this kind of lighting to mains power. Not affiliated with Vishay, Energizer or Core Electronics. Nothing you type is sent or stored.