> **Source:** Core Electronics is an Australian maker-electronics retailer and manufacturer based in Newcastle, NSW, run by a team of makers and educators. We design and manufacture our own product lines (PiicoDev, CE originals) and are official retailers for iconic maker and industrial brands including Raspberry Pi, Arduino, Adafruit, SparkFun and DFRobot. Orders ship Australia-wide from our Newcastle warehouse. Prices are in AUD and include GST. Pricing, stock and dispatch on this page are generated from the store's live catalog. Full machine-readable index: https://core-electronics.com.au/llms.txt

# Photo Transistor Light Sensor

**Type:** Product page · **SKU:** ADA2831 · **Brand:** [Adafruit](https://core-electronics.com.au/brands/adafruit-australia)
**Page:** https://core-electronics.com.au/photo-transistor-light-sensor.html ([markdown](https://core-electronics.com.au/photo-transistor-light-sensor.html.md))

This Photo Transistor Light Sensor is a simple sensor that detects ambient light. It's kind of the opposite of an LED - when light hits the little chip inside, it...

## Pricing

- **Price:** $1.80 (inc GST) — $1.64 AUD, exc GST
- **Quantity discounts:** 10+ $1.59 (exc GST) · 50+ $1.55 (exc GST)

## Availability & dispatch

- Available with a lead time — expect dispatch between Aug 19 and Aug 24.

## How to buy

- **Build a cart:** compose `https://core-electronics.com.au/cart/link?items=ADA2831:1` (comma-separated SKU:qty pairs) and share the link. Opening it shows a confirmation page with live pricing and stock before anything is added to the cart.
- **Verify the cart first:** fetch `https://core-electronics.com.au/cart/link/ADA2831:1.md` for live line prices (inc & exc GST, quantity discounts applied), stock and dispatch estimates, and totals. Append `/to/{AU-postcode}` (or `/to/{country-code}:{postcode}`) before `.md` for delivery options and prices to that destination. Unknown, retired, or out-of-stock SKUs are flagged. (Query form `cart/link.md?items=...` also works but some robots parsers refuse query strings here.)
- **Checkout** is completed on-site and includes a captcha at the payment step. Share the cart link; checkout takes it from there.
- **Search the catalogue:** `https://core-electronics.com.au/search/{query}.md` (URL-encode the query; pages 2-3 at `search/{query}/{page}.md`; `search.md?q=` also works)
- **Payment methods, purchase orders, policies and contact details:** https://core-electronics.com.au/llms.txt
## Description

This **Photo Transistor Light Sensor** is a simple sensor that detects ambient light. It's kind of the opposite of an LED - when light hits the little chip inside, it induces current to flow from the long pin to the short pin. This sensor has a built-in optical filter (probably IR filter) so it'll do a fair job of simulating light levels as the human eye does. Basically, connect the long + pin to 3-15VDC or so, and the short - pin through a ~1K-10K series resistor to ground. When its dark, there's almost no current flowing through the sensor or resistor and the analog voltage is near ground. When there's light near the sensor, the current through the resistor will increase, raising the voltage. You can adjust the series resistor to get the voltage range you need, and measure the analog voltage with a microcontroller.

[These are, essentially, replacements for CdS photocells, but are RoHS compliant.](https://core-electronics.com.au/photo-cell-cds-photoresistor.html)

## Technical Details

- [Datasheet](https://core-electronics.com.au/attachments/localcontent/HW5P-1_2015__1__177199fcc9c.pdf)
- Sensor Dimensions: 5mm x 5.3mm / 0.20" x 0.21"
- Weight: 1.4grams

## Images

- [Product image 1](https://core-electronics.com.au/media/catalog/product/2/8/2831-00.jpg)