As a Software Engineer at Sunlighten, you play a pivotal role in shaping innovative software solutions that enhance the user experience and operational efficiency of our products. This position is critical in developing software for connected devices and integrating advanced technologies that support our mission of improving health and wellness through innovative products. You will engage in projects that directly impact how users interact with our systems, ensuring that our software is not only functional but also user-friendly and reliable. The complexity of the software you will work on ranges from backend services to frontend interfaces, collaborating across teams to create cohesive and effective solutions. You will work on projects that push the boundaries of technology while being part of a culture that values creativity, collaboration, and continuous improvement. This role offers an exciting opportunity to work on diverse challenges that impact our business and our customers, making your contributions both significant and rewarding.
Initial Phone Screen
reportedFocuses on your resume and technical background.
What to demonstrate
- Focuses on your resume and technical background
- Depth in Connected Devices (IoT)
How to prepare
- Be able to walk your CV end to end in two minutes, and say why this company specifically.
- Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
Technical Interviews
reportedDive deeper into your coding and problem-solving abilities.
What to demonstrate
- Dive deeper into your coding and problem-solving abilities
- Depth in Connected Devices (IoT)
How to prepare
- Answer aloud and timed: Describe a challenging bug you encountered and how you resolved it.
- Answer aloud and timed: How do you ensure the security and integrity of your code?
Behavioral Interview
reportedAssess cultural fit and interpersonal skills.
What to demonstrate
- Assess cultural fit and interpersonal skills
- Depth in Connected Devices (IoT)
How to prepare
- Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
- Re-read the description of the behavioral interview above and write down what you would ask to confirm before it.
PracHub editorial advice for the preparation topics above.
Understand Company Values
Familiarize yourself with Sunlighten's mission and values to demonstrate alignment during your interviews.
Practice Coding
Regularly practice coding challenges, particularly in your preferred programming languages, to stay sharp.
Engage in Mock Interviews
Conduct mock interviews with peers to simulate the interview environment and receive constructive feedback.
Be Transparent
If you encounter questions you’re unsure about, it’s okay to express your thought process and reasoning during the interview.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Write a function to reverse a string in your preferred programming language.
Write a function to reverse a string in your preferred programming language.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Given a list of integers, find two numbers that add up to a specific target.
Given a list of integers, find two numbers that add up to a specific target.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Explain the difference between a stack and a queue and provide use cases for each.
Explain the difference between a stack and a queue and provide use cases for each.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Keep soft-deleted accounts from blocking re-registration
app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.
Approach
- Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
- Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
- For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
- State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.
Follow-up
- A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
- How do you honour an erasure request while resource_revision.actor_user_id still references this table?
Hold a per-tenant active cap against concurrent creates
A tenant on the standard plan may hold at most 50 resources with status='active'. The create handler runs SELECT count(*) FROM resource WHERE tenant_id = $1 AND status = 'active', compares to 50, then inserts. Two creates arrive 3 ms apart on different instances and the tenant lands at 51. Name the anomaly, say whether PostgreSQL 16 READ COMMITTED or REPEATABLE READ prevents it and why, then give an implementation that holds the cap at READ COMMITTED with the exact statements. Finally, say what changes when the cap is 'at most one running export per tenant' on job_run.
Approach
- Name it: write skew. The two transactions read an overlapping set and write disjoint rows, so there is no row-level conflict for the engine to detect and each commit is individually legal.
- Rule out the levels precisely. READ COMMITTED takes a fresh snapshot per statement and takes no lock on the counted rows, so both see 49. PostgreSQL's REPEATABLE READ is snapshot isolation: it removes non-repeatable reads and phantoms within the snapshot but still admits write skew, because the anomaly is not a re-read of a changed row, it is a read of a set that a concurrent transaction invalidates. Only SERIALIZABLE closes it, by tracking the read dependency and aborting one transaction with SQLSTATE 40001 — a guarantee that exists only if the application re-runs the whole transaction from the read.
- Convert the set predicate into a single-row conflict: keep tenant.active_resource_count and run UPDATE tenant SET active_resource_count = active_resource_count + 1 WHERE tenant_id = $1 AND active_resource_count < 50 in the same transaction as the INSERT. Zero affected rows is the cap, returned as 409. The row lock serialises the decision at any isolation level, and contention is bounded to one tenant's row — which is also the fair-scheduling unit, unlike a global counter that would convoy every tenant behind one row.
- State the cost you just took on: a counter is a second source of truth that can drift, so every path that changes status must adjust it inside the same transaction, and a periodic reconciliation has to exist, with resource_revision as the authority for what the count should have been.
Follow-up
- A resource moves from archived back to active. Which statements change, and what breaks if the counter update and the status change land in different transactions?
- The cap becomes plan-dependent and a plan can change mid-month. Where does the number 50 live, and who reads it?
What programming languages are you most proficient in, and how have you applied them?
What programming languages are you most proficient in, and how have you applied them?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe a challenging bug you encountered and how you resolved it.
Describe a challenging bug you encountered and how you resolved it.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How do you ensure the security and integrity of your code?
How do you ensure the security and integrity of your code?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What tools do you use for version control and why?
What tools do you use for version control and why?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you design a system to handle a large number of simultaneous users?
How would you design a system to handle a large number of simultaneous users?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
What architectural patterns do you prefer, and why?
What architectural patterns do you prefer, and why?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Can you walk us through a system you designed from scratch?
Can you walk us through a system you designed from scratch?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
How do you approach database design for a new application?
How do you approach database design for a new application?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
How would you approach optimizing an existing application for performance?
How would you approach optimizing an existing application for performance?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What steps would you take to troubleshoot a system outage?
What steps would you take to troubleshoot a system outage?
Approach
- Establish what changed and when, before forming any theory.
- Pick a bisection that eliminates candidates whichever way it turns out.
- Check the instrumentation before believing the symptom.
- Separate the trigger from the cause; the deploy is rarely the bug.
Follow-up
- What would you look at first, and what would it rule out?
- How would you tell a cause from a coincidence here?
Built from the rounds and topics Sunlighten candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Sunlighten loop
- Write out the reported sequence: Initial Phone Screen, Technical Interviews, Behavioral Interview.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.
02Work Connected Devices (IoT)
- Spend the session on Connected Devices (IoT), which Sunlighten candidates report being tested on.
- Write one worked example in Connected Devices (IoT) and time yourself on it.
Deliverable: One timed worked example in Connected Devices (IoT).
03Work Shopify Plus Development
- Spend the session on Shopify Plus Development, which Sunlighten candidates report being tested on.
- Write one worked example in Shopify Plus Development and time yourself on it.
Deliverable: One timed worked example in Shopify Plus Development.
04Work Full-Stack Development
- Spend the session on Full-Stack Development, which Sunlighten candidates report being tested on.
- Write one worked example in Full-Stack Development and time yourself on it.
Deliverable: One timed worked example in Full-Stack Development.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: Explain the software development lifecycle and your experience with it.
- Answer aloud, timed: What programming languages are you most proficient in, and how have you applied them?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: System Design / Architecture
- Answer aloud, timed: How would you design a system to handle a large number of simultaneous users?
- Answer aloud, timed: What architectural patterns do you prefer, and why?
Deliverable: Spoken answers to 2 reported System Design / Architecture question(s), under time.
07Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Describe a time when you had to work with a difficult team member. How did you handle it?
- Answer aloud, timed: What is your approach to receiving and giving feedback?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Explain the software development lifecycle and your experience with it.
Explain the software development lifecycle and your experience with it.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a time when you had to work with a difficult team member. How did you handle it?
Describe a time when you had to work with a difficult team member. How did you handle it?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
What is your approach to receiving and giving feedback?
What is your approach to receiving and giving feedback?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Share an example of how you have motivated a team to achieve a goal.
Share an example of how you have motivated a team to achieve a goal.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you prioritize tasks when managing multiple projects?
How do you prioritize tasks when managing multiple projects?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a time when you had to make a critical decision with limited information.
Describe a time when you had to make a critical decision with limited information.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
Explain the software development lifecycle and your experience with it.
- 02
Describe a time when you had to work with a difficult team member. How did you handle it?
- 03
What is your approach to receiving and giving feedback?
- 04
Share an example of how you have motivated a team to achieve a goal.
How difficult are the interviews, and how much preparation time is typical?
The interviews at Sunlighten are considered moderately challenging, with a focus on both technical and behavioral aspects. Candidates typically prepare for 2-4 weeks, depending on their familiarity with the technologies and concepts involved.
Sunlighten Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates demonstrate a strong combination of technical skills, problem-solving abilities, and cultural fit. They are prepared to discuss their past experiences and how they align with Sunlighten's mission.
Sunlighten Software Engineer candidate reports ↗What is the culture and working style at Sunlighten?
Sunlighten fosters a collaborative environment that values innovation and creativity. Team members are encouraged to share ideas and contribute to projects that enhance user experience.
Sunlighten Software Engineer candidate reports ↗What is the typical timeline from initial screen to offer?
The interview process can take 3-6 weeks, depending on scheduling and the number of interview rounds. Candidates should remain patient and engaged throughout the process.
Sunlighten Software Engineer candidate reports ↗Are there remote work or hybrid expectations?
Sunlighten supports flexible work arrangements, including remote work options, depending on the role and team dynamics.
Sunlighten Software Engineer candidate reports ↗What topics does Sunlighten test in interviews?
Sunlighten interviews most often cover Connected Devices (IoT), Account Executive (AE) Sales Process, Shopify Plus Development, Inside Sales, and Full-Stack Development. The exact emphasis depends on the specific role you apply for.
Sunlighten Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Sunlighten Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
Explore related engineering environments and compare the preparation focus.
Vercel Software Engineer Interview Guide
Debugging practice for Vercel software engineer prep built on a reproduction you trust, narrowing to the smallest failing input, and changing one variable per run so the result stays attributable.
Spotify Software Engineer Interview Guide
Timed practice for Spotify software engineer candidates who lose time to the clock: short problems taken end to end, then reviewed against a written rubric rather than a passing test run.
Scale Ai Software Engineer Interview Guide
Data structures and algorithms practice for Scale Ai candidates, where stating a bound means stating its precondition: constant-time hash lookup is an average case over keys that spread.
Ramp Software Engineer Interview Guide
Systems practice for Ramp software engineer candidates, weighted toward payments and lending work: the load that actually arrives, the failure modes that matter there, and the invariants a partial outage must not break.